Gasoline & Oils  Pertaining to 2 Cycle Outboard Motors


History :  Prior to the early 1920s, automotive fuel was essentially refined crude oil into liquid gasoline, or petrol as it is known in other parts of the world.

Up until this time, gasoline tended to pre-ignite or detonate, causing a metallic 'pinging' sound, a situation called engine-knocking, that could cause engine damage if subject to continued use.   The additive of the chemical element in the form of Tetraethyl lead (TEL) gasoline changed that.   Not only did leaded gasoline withstand higher compression environments, but also lubricated the inside and valves of the engine, protecting the valve seats from erosion while lubricating the valve stems at the high temperatures they were subject to.   To read the history of automotive fuels CLICK HERE.

In the early years, the automotive industry had not developed steel yet that would not gall in a high temperature situation where the valves operate in a engine.  So this lead additive accomplished a twofold result of controlling the combustion while lubricating the valve seats and stems.

The leaded fuel also caused problems of it's own.   In the past, lead deposits on spark plugs were the main reason to change them so often.

The Clean Air Act Amendments of 1990 mandate the elimination of lead from all U.S. motor fuel by January 1, 1996.  This represents the final step in a gradual reduction of lead in gasoline since the early 1970s when the engines were starting to be redesigned with anti-pollution in mind.  The use of catalytic converters in the exhaust system probably was the final lead killer.  With the inception of this converter, it could digest the leaded exhaust and get plugged up if leaded fuel was used for any length of time.

How Does This Relate to Boaters ?   It is not really known as to whether that this lead additive is what caused the varnish in gas tanks and carburetors if let set for a period of time, but since the non-leaded gasoline has became the norm, the varnish or a jellied mass has about vanished from the scene.  Thereby indicating to me at least, that the new unleaded gasoline is more stabilized than the leaded.

In accordance with the Federal Clean Air Act (CAA) of the Environmental Protection Agency, (EPA) establishes fuel quality standards to help protect public health and the environment from harmful gas and particulate matter emissions from motor vehicles and engines.  here is a link to the Government regulations, -

EPA issued standards in 1973 that called for a gradual phase down of lead to reduce the health risks from lead emissions from gasoline.  Beginning in 1989, EPA required gasoline to meet volatility standards (in two phases) to decrease evaporative emissions of gasoline in the summer months.  Upon passage of the 1990 CAA amendments, EPA began monitoring the winter oxygenated fuels (Ethanol) program implemented by the states to help control emissions of carbon monoxide.  It also established the reformulated gasoline (RFG) program, which is designed to reduce emissions of smog-forming and toxic pollutants.  EPA also set requirements for gasoline to be treated with detergents and deposit control additives.  More recently, EPA has set standards for low sulfur gasoline and low sulfur diesel, which will help ensure the effectiveness of low emission-control technologies in vehicles and reduce harmful air pollution.

Do not use premium fuel in your water cooled 2-stroke boat motor unless it was designed to run on it.  Higher octane fuels burn slower and cooler, that's why they're used in high compression engines.  Slower and cooler burn rates in low compression 2-stroke engines results in a loss of performance, increased carbon build up, and more expensive exhaust.  You gain nothing by using higher octane fuel and may very well add to problems.  Spend the money you save by using proper octane fuel on a good fuel stabilizer, fresh plugs and an impeller at the recommended interval.

Ethanol Gasoline :  From about mid 2000 year, we are seeing most of the fuel being an E10, or 10% alcohol.  This formulation is NOT good news for the boating industry/owner.  This fuel can effect the older rubber fuel lines by softening them, allowing them to collapse internally.  So you may need to replace your fuel lines with the newer alcohol resistant lines.   An interesting feature of Ethanol in gas is its cleaning ability.   It will over time remove all those old layers of varnish from previous gasoline which then gets deposited in the fuel filter, plugging it and anything that gets thru the filter ends up in the carburetor or injector making life miserable for the boat owner/mechanic.

Gasoline is made without additives and delivered in that form to the distributors.  These distributors add the additive depending on who it is sold to.  It appears that each state's laws may be different in relationship to Ethanol blended fuel.  A few states allow premium gasoline to not be the E10, but most are blended.   CLICK HERE for an explanation.

Outboard motor owners who have no choice of gasoline should not try to not use fuel that is over 3 months old, stabilizer will help for another couple of months, but it may be beneficial to drain out the old fuel in the spring of the year, use it for your old truck, lawn mower or something that can be pushed home instead of towed.   ARCO brand was the first since about 1999 usually has 10% alcohol in it and is actually called gasohol by some.  As of 2008 about all gasoline companies have added a blended gasoline at the pumps.  This is bad news to those of you boaters who refuel at automotive stations may not use enough weekly to keep fresh gas in your tank.  This alcohol additive may soften your fuel lines, fuel pump diaphragms, carburetor gaskets & not be compatible with some of the older motors. 

Ethanol Detection - Water Extraction Method ;  Alcohol can be detected in gasoline using the Water Extraction Method, in which alcohol blended with gasoline will react differently with water then unblended gasoline.   A gasoline sample should be taken in a glass vessel, after which water should be slowly added to the container to a level of approximately two inches.   Once the gasoline and water have settled and distinctly separated, the container should be marked at the phase separation point.   Once the container is clearly marked, it should be agitated for one minute, after which the contents should again be allowed to settle.  

An alcohol blended gasoline will show a larger lower phase at this point, due to a phase separation of the ethanol and gasoline.   In effect, the lower phase is now water AND ethanol with the upper phase being unblended gasoline.   Once the ethanol and gasoline are separated, they cannot be reblended via agitation; this phase separation is a one way process.   If the sample taken is pre gasoline, the water will settle at the previously marked level, with no apparent increase in the lower phase of the container.

In the photo below on the left, you can clearly see the milky color of the Ethanol absorbed water.  The photo on the right shows what the Ethanol can do the the older style shellacked carburetor float, not to mention all the brown residue from the dissolved shellac left inside the bowl & the plugged jets.

Here is an example of Ethanol fuel that was drained out of a outboard fuel/water separator that had absorbed a goodly amount of water

"Marine Grade Gas" sold at marinas, or agricultural gas stations are exempt from having to add this Ethanol to their fuel.  Some farm store fuel stations advertise "no ethanol" and may suggest that it remains stable for a year without fuel stabilizers.    For a link to fuel locations that sell non-ethanol fuel CLICK HERE.   However for the boater, it may be better safe than sorry and add a stabilizer anyway.

There are two things that will deteriorate gasoline rapidly.  They are (1) exposure to Oxygen, (2)  heat.  So if you have to store a amount of gasoline for any length of time, if you can combat these 2 items, your gasoline will last longer even without having to be stabilized.  This is fact, but I am not recommending that you go out and purchase 350 gallons of gasoline, store it properly if intend to keep it for future usage if you only use 10 gallons a month even if you add stabilizer.

I have had six 5 gallon cans of gasoline stored in my barn for a year because my boat motor sucked a piston at the start of the fishing season and I did not get it back for 8 1/2 weeks which lost my whole fishing season.  I did add the stabilizer additive when I realized I would not be able to use it when I had thought.  The next year's fishing season when I used it I could not tell any difference in the boat's performance.

The word is, the longer it sits the worse it gets.   However those folks who use their boats more often or are able to store it indoors seem to have far fewer problems than those who don't.  Fishing guides don't have issues because their gas never sits for any time, those fishermen who put away a boat outdoors in Sept and don't touch it until April have issues others don't see.

Click HERE for a link to BoatUS Marine Insurance editor's take on ethanol fuel for boaters.

Gasoline Shelf Life :    According to Chevron....  "Gasoline stored in a tightly closed container in a cool place will stay good for at least a year.  It is better if the container or gas tank is almost (95%) full.  If the container or gas tank will be in the direct sun or will be heated above 80 degrees F. much of the time, add an aftermarket fuel stabilizer to the gas when you first buy it.  Gasoline-oil blends for two-stroke cycle engines stored under the proper conditions will keep as well as gasoline itself."

The oil additive therefore does not make any difference in storage life.

And this from Shell.... "All gasoline has finite storage life.  If storing gasoline longer than 6 months, you may want to use a supplement fuel preservative additive".

If aged long enough, gasoline can form gum and varnish that can cause engine operating problems, sometimes to the engine and fuel tank.  All Shell gasoline - conventional and reformulated - meet ASTM requirements for stability (a measure of protection against oxidation that can degrade gasoline properties).  How long gasoline can be stored, depends mostly on storage conditions.  Increased temperature, exposure to air and contaminates, and the material the storage container is made of can shorten storage life.  Generally, gasoline stored for longer than 6 months will likely benefit from adding a supplemental stabilizing additive.  Usually available at your Shell service station.  Stored gasoline only in an approved container, well away from sources of ignition."

For tanks that are mostly full and going to be left for a considerable length of time, add a fuel stabilizer.  Premix a couple of gallons of gas with enough stabilizer for the total amount in the tank, then add this mixture into the tank.  Different stabilizers give different "life" times, so therefore some brands of stabilizers "do" more.

Here is a a link to The 411 on Ethanol  Everything you need to know about the Ethanol in your fuel and your equipment !

Now for my opinion on this BS.  The above oil companies are just like politicians, they say a lot but, are only trying to cover their behinds.  From my observations, I think that the newer non-leaded non Ethanol fuels produced by modern technology aren't anywhere near prone to "varnish" as the older leaded gasoline was.  My thought is that it would take serious neglect and long, long periods of storage to form "varnish" in a current fuel system.  I suspect that long term storage in a steel fuel tank would be more detrimental because of possible rusting of the steel tank, especially Ethanol blend which may plug the fuel filter or get by it & into the carburetor.

Currently just how many of you just park your lawn mower after the mowing season, and it will start the next year with only a few pulls of the rope, way better than in years past.

Now I will relate my experience with long term boat fuel storage.  I, for various reasons quit using a boat in July of 2004, then it had about 1/2 a tank (30 gallons left) of non ethanol non stabilized fuel.  This boat was stored in side a non heated RV shed all the time.  When I sold it in November of 2009, it started fine, but smoked considerably at first.  The fuel had a bad smell, but the motor ran on the muffs quite well.  The new owner just pumped the fuel old out, added more and it has ran fine since.

In the years not so far in the past, most gasoline was leaded 85 octane.  The final end result is that all medium grade gasoline now being sold is non-leaded 87 octane, it is hard to find the older lower 85 octane, at least in the western states.  And if you do find it, the low advertised pump price will be for the 85 octane.  You will find that most newer vehicles are not recommended for you to use 85 octane, if you do, your efficiency and mileage will be lower in the long run so in actuality the 87 octane is cheaper.

Most outboard motor manufacturers now recommend a 87 octane non-leaded gasoline. As of, 2009, we see much of our gas has Ethanol mixed into it at a rate of 10% .

Now comes the sticker.  A friend of mine who spent his whole working life associated with a well known farmers CO-OP delivering fuel, told me a few years ago that there is a Summer Gas & a Winter Gas.  The difference is that Winter gas had an additive to allow the motors to start at a colder condition.  He said if you are going to purchase any gasoline to keep in storage for a while, purchase it early in the fall, so it was Summer gas and not Winter gas.   My guess is that this additive he was referring to was Alcohol.   And now they appear to be selling "winter" gas year round, with the higher ethanol content being high year round that we now know as E10. 

To Store Your Boat With a Full or Empty Fuel Tank ?? :   To view this article CLICK HERE.

Fuel to Oil Mix Ratio For 2 Cycle, Water Cooled Outboard Motors:   The reason for mixing oil into the gasoline is that since these engines are 2 cycle (sometimes called 2 stroke) which fire on each stroke of the piston, there needs to be oil mixed into the gas to lubricate the internal parts of the engine (piston, crankshaft and bearings), as there is no crankcase oil reservoir or oil pump as in the 4 stoke engines.

In the early years for 2 cycle motors, the standard oil mix was 30W SAE automotive oil.   A lot of improvements have been made in motors and the oil since those days.  These early outboard motors used bronze bearings for both the main and rod bearings which needed a lot of lubrication.  The recommended fuel / oil mix was 16 to 1 or 25 to 1.  After about 1965 depending on the brand of outboard, the motors were designed to use ball bearings for the main bearings and needle roller bearings for the rods.  That is when the newer 50 to 1 oil ratio was introduced.

This following is per BRP which is now the current manufacturing company of Johnson/Evinrude;  What is the fuel/oil mix for my motor?
The following is generally true: 1958 and prior used 20 to 1, 1959 thru 1963 used 24 to 1, 1964 and newer use 50 to1.  New engine break-in of post 64 motors is recommended at 25 to 1. "High performance usage" (racing) of post 64  is also recommended at a ratio of 25 to 1.

From 1985 to 1989, Johnson and Evinrude (OMC) recommended a 100 to 1 mix, this was printed on a decal placed on motors of these years.  The actual change back to the 50 to1 mixture was made sometime in 1989.  There was a Technical Bulletin  #2162 dated March 1986, directing the mechanics to remove the decal,  replace it with a new 50/1 decal and inform the owner, when the motor was serviced in an OMC repair shop.  This was recommended for rental, commercial and heavy duty service engines.  The suspicion apparently was that some motors, under the right (or wrong) conditions, if ran at a high RPM or under a load for extended periods of time, may seize due to lack of adequate internal lubrication.   However info from an OMC technical representative is more believable in that if a boat has an internal tank, it was hard for the owner to accurately measure the premix oil quantity at the time of refueling, not knowing the exact amount of fuel is actually being added until the fueling is finished.   Where it is recommended to add the oil beforehand so the mix blends better and is more complete.  Smaller motors using removable 6 gallon tanks are easier to estimate the amount of oil needed.

The fuel/oil mix recommended by the outboard manufacturers since about 1960 is listed at 50 to1.  This means 50 parts of unleaded 87 octane gas to 1 part of TC-W2 or TC-W3 outboard motor oil.  You probably will not see much of the older TC-W2 oil out there anymore since about 1996 or so.   The only difference between the TCW II(2) and TCW III(3) is that TCW III is certified for use in separate oil-tanks like the VRO, Variable Ratio Oil injection motors.  It has a higher resistance of forming 'gel' in humid conditions that prevents oil-filters to be clogged up.   Mixed in fuel no difference between any of the TCW oils, however unless you uncover some TCWII from a old stash, it makes little difference as is not made anymore.

The oil designated for 2 cycle outboard motors is TWC-3, this code represents,  Two cycle, Water Cooled, type 3 formula.  The formula 3 also has decarbonizing additives designed to be more compatible with the newer non-leaded fuel.   There is now no detergent / non-detergent outboard motor oils, just the TC-W3.   Four cycle motors generally use FC-W. Four Cycle - Water cooled.   Both differentiate from air-cooled motors such as chain saws, which use a different oil.

TCW-3 oil has a dye in the oil so when mixed with the fuel, this fuel will be colored to help the consumer verify that he mixed in the oil.  Wallyworld and Starbrite oil is blue, Mobil oil is red, some Pennzoil was green, and if memory is right, the Texaco oil was purple.  These may not be exact, but you get the idea.

For the oil to be certified TC-W3, samples have to be submitted to a laboratory and extensive tests ran.  Here is the NMMA website that lists all those oils tested and passed. 

A marine mechanic once told me that all TC-W2 oils were regular petroleum oils while the TC-W3 were synthetic oils, however it seems he was misinformed as I have found out differently.  My research is that apparently the oil industry and boat motor needs have now gone beyond the specifications for TC-W3.   Some oil manufactures do make a synthetic blend (sometimes called semi-synthetic) or even pure synthetic oil, and since there is not a higher category NMMA in existence, the oil companies list that it meets OR exceeds the TC-W3 specifications as there is nothing currently specified in the industry yet to designate synthetic oils. 

The formula shown below will be on all modern 2 cycle oil sold in the last 30 years or so.  On most all of the pints and quart plastic bottles of TWC-3 oils there will be a narrow clear vertical window on the edge of the bottles.  On the sides of this window will have numbers representing ounces and Milliliters for other parts of the world.  Or you can purchase special measuring containers showing different ratios & the amount of ounces needed.

If your motor is to where you have to mix the oil, you need to know how much gasoline you will be needing, add the oil before you fill the fuel tank so that the oil mixes better that just dumping it in after you fuel up.  However if that is not possible, guess, add a majority of what you think it will take, fuel up, then add the rest matching the amount of gasoline you took on.  If you are using portable fuel thanks, before hand, when you fill it, add 1 gallon at a time, use a clean 3/8" or 1/2" dowel, mark the dowel at each gallon and use it as a measuring stick.  This way you can refill a partly full tank with the known amount of oil.

A quart has 32 ounces of oil in it.  So for a portable 6 gallon tank to fill it using the 50:1 ratio would take 16 ounces, (1 pint) or 1/2 of the quart.


Gallons of Gasoline

Gasoline to Oil Ratio

Ounces of Oil to be Added

16:1 24:1 32:1 50:1 100:1
1 8 5 4 3 2
2 16 11 8 5 3
3 24 16 12 8 4
4 32 21 16 11 6
5 40 27 20 13 7
6 48 32 24 16 8

You can spend your money and purchase non synthetic OMC oil, or any other outboard manufacturers oil for about $6.50 a quart, or buy a name brand quart for $3.49.   Synthetic oil is about $8.50 a quart.   Sure the manufacturers want you to buy their oil, and for a new motor under warranty, it may be advisable to do so.   But the consensus from many experienced boaters is to use any good brand of oil for normal boating needs, as long as it has the TC-W3  rating, it meets or exceeds the manufacturers specifications.  Large motors pushing a heavy load for extended periods of time, or smaller trolling motors idling for extended periods of time may be something different & looking into the blended or synthetic oils may be beneficial here.  

Some dealers may try to tell you that new motor warranties are void if oils other than original manufacture brand oils are used and a internal mechanical failure happens.  There was a court ruling on this several years ago based on the Magnuson/Moss directive.  This ruling was that for this requirement to be valid, the manufacturer/dealer MUST supply the required oil at no cost to the consumer.  The "law" basically says the manufacturer can't specify a BRAND NAME of oil, unless THEY provide the oil.   However manufacturers can specify certain grades, (TCW-3) etc. and deny warranty work IF those specific oils are not used.  It is very difficult to argue that cheaper certified TCW oils don't give long life for the average boater -- there are too many motors running out there that say it does.  However it is hard to compare one owners usage with another owners, even using identical motors because of how hard the hand is on the throttle.

So you are really at the mercy of the oil companies in trying to decide just what they are saying in their advertisements.  Lots of talk at times, but not really saying much that is understandable.

Mixing a less standard oil than recommended in the fuel makes the engine run leaner and warmer (less power, causes detonation, and overheating, but more important, could cause the motor to seize up), more oil makes the engine run rich and fowls plugs (less power too), forms carbon deposits & friction can increase because of the carbon builds up, so more heat is also made.  Therefore a happy medium needs to be achieved depending on your usage.

If you try to lessen the oil ratio, and yet run it at higher speeds, you then will possibly run into other major internal problems in the long haul.  This may not only be for proper crankshaft / rod bearing / piston wall oiling, because 2 strokes burn hot when run lean and you can likely get a partially melted piston top in the lower cylinder.  To avoid this possible damage, and a melt-through of the complete piston top, you need to be aware that this can happen on a lean condition.  If in doubt, the safe solution is to run the correct fuel to oil mixture ratio of 50-1.

Now all the above information is directed to usage in WATER COOLED outboard motors.  Back in the 1950s & 1960s, you had air cooled 2 cycle outboard motors.  In mixing fuel for these, use the same ratio as weed whackers or chain saws.

Fuel Additives :   There are many companies making fuel additives that are used or designed to be on boat engines.  Some have great claims.  Some simply are a fuel stabilizer, while others do many things, like stabilizing, loosening gunk cleaning the fuel tank & engine, emulsifying the water & gasoline, even neutralize the 2 stoke unburned oil & keep your motor/ transom clean.  A few are listed below.

( STA-BIL)  Fuel Stabilizer eliminates the need to drain fuel during storage, and keeps fuel fresh for up to 12 months or more. STA-BIL now includes more corrosion protection than ever before to help prevent and protect against problems caused by today’s Ethanol-blended fuels. 

For Marine Formula STA-BIL Ethanol Treatment and Performance Improver contains DOUBLE the corrosion preventers and more than FOUR TIMES the fuel system cleaner than in Regular STA-BIL to prevent against corrosion and deposit build up in Marine Engines.  Use AT EVERY FILL UP to protect your boat or other marine equipment from the damaging effects of Ethanol in the marine environment

1 oz.  for every 2 ˝ gallons of gasoline, gasoline/oil mixtures, or ethanol blends.   16 oz. treats 24 gallons of gasoline.

(SeaFoam) This is a nationally known product sold thru both automotive and marine dealers.  On the can it says  - A 100% pure petroleum product for use in a; gasoline and diesel type engines. both 2 and 4 cycle.  Oxygen sensor safe.  Cleans dirty engine parts internally by removing harmful gums, varnish and carbon.  Works and performs instantly.  Removes moisture from old crankcases and fuel tanks.  Stabilizes and conditions fuels.  Use for engine storage. Cures hesitations, stalls, pings and rough idle due to carbon build up.  Helps pass emissions tests.  EPA registered. Can be used for fogging  for winter storage.   Tested to 60 degrees below zero.  Made since 1942

16 oz. treats 50 gallons of gasoline fuel, or 25 gallons (2 oz per gallon) of gas / oil premix.

(Startron)   This additive is sold by West Marine. A 16 oz. bottle normally sells for $21.99, however you may find it on sale for $16.49.  Their catalog says -- New enzyme-based additive increases fuel economy and engine power while reducing emissions.   Stabilizes gas for short and long term periods of inactivity (up to one year) while preventing the formation of varnish.   Eliminates carbon buildup in fuel delivery system and exhaust components.   Increases octane and removes water from the fuel, making it the perfect solution to prevent and eliminate ethanol (E-10) fuel problems.  Fights organic growth without biocide!  Reduces fuel consumption and engine wear while increasing power.  Enzymes treat water in fuel.   For use with any engine; not toxic to the environment.

16 oz. treats 256 gallons of gasoline.

(Soltron)   Retail price is normally at about $20 for a 16 oz. bottle.  This is called an enzyme fuel treatment and uses 100% natural enzyme technology to deliver multiple benefits to all gasoline and diesel engines.  Effects can be felt in as little as 30 minutes.  Don't worry about using too much as it is pure fuel and harmless to any engine.  It is a powerful dispersant and may loosen and dislodge heavy accumulations of sludge, including deposits caused by overuse of other fuel additives.  Fuel filters may require servicing when first using SOLTRON in contaminated fuel.  Removes bacteria and mold, cleans injectors and will rejuvenate ethanol water separated fuel.

Many boaters of 2 cycle motors report that this product eliminates the black carbony stains on the stern and motor parts at water level,

16 oz. treats 500 gallons of fuel or 1 oz per 30 gallons.  This amounts to about 3/16 oz per 5 gallons.  The old bottle is marked in 1 oz. divisions. 

A salesman for Soltron says that Startron is the same product as Soltron, except in a weaker (near 50%) concentration.

(Yamalube Fuel Stabilizer and Conditioner PLUS)    Strongly recommended for E-10 fuels, this alcohol-free formula helps prevent fuel oxidation and phase separation from moist, rich air. When used continuously, it keeps fuel fresh, potent and free from gum and varnish for up to one year of storage. Its metal filmers, provide extensive protection for steel and aluminum components.

Alcohol-free Yamalube Fuel Stabilizer & Conditioner PLUS is specially formulated to help protect your engine's fuel system from the harmful effects of ethanol-enriched fuel, including its corrosive effects on metals as well as fuel system gum & varnish that can result from fuel oxidation. Also effective with non-ethanol fuels. When used as directed, helps keep fuel fresh & potent during normal use.

For maximum fuel system protection, use this product on a continuous basis.   Add 3.2 oz. bottle of Yamalube Fuel Stabilizer & Conditioner PLUS to every 5 gallons of fresh gasoline.  
16 oz. treats 25 gallons of gasoline.

For off-season storage ask your Yamaha dealer for the concentrated version in 12 oz. & 1 quart bottles.

Yamalube Fuel Stabilizer

Outboard Oils :   There are very few subjects that stir the emotions of the outboard motor user more than to ask, "what 2 stroke oil do you use and why"?

If you wan to identify the actual manufacturer of a TCW oil CLICK HERE

Two cycle oils compose from 50% to 95% of the total weight of the 2-stroke engine oil.  They fall into 2 general categories: synthetic and petroleum based.   Since synthetic oils are not manufactured from petroleum, there has been a lot of questions flying around in the last several years about what really constitutes a ‘true synthetic’ oil.  There is no universally accepted definition for synthetic oil.   Each manufacturer is free to label their product "synthetic" by whatever rules the manufacturer chooses.   Also what exactly is a blended oil?  What percentage is this blend?

Due to the nature of the carburetored two cycle marine engines, fuel is mixed with oil which then lubricates the engine parts as it passes through the engine during the combustion cycle.   This is in contrast to four cycle engines which have oil sumps and pumps for lubricating the engines, and the fuel is not pre mixed.

The long term objectives of the two cycle engine industry have been to reduce emissions which contain burnt and unburned oil that has passed through the engine, and to develop a quality of oil that reduces the mixture ratio to fuel while extending the life of the engine.   That means significantly reduced emissions to satisfy EPA requirements, less warranty problems, and increased customer satisfaction due to engines lasting longer with less maintenance and overhauls.  In 2006, with the new Federal EPA emissions standards for outboard motors being kicked in, even more emphasis on a better 2 cycle oil is needed.

TC-W3® lubricant, an NMMA owned trademark, has evolved over the years through much testing and research, and has proven to be the level of quality to satisfy the above objectives.  And, going a step further, now that two cycle engines have moved towards higher cylinder temperatures and compressions, this lubricant also meets the EPA emissions reductions.

TC-W3 has demonstrated the necessary lubrication performance quality needed for these more demanding cylinder/engine conditions in the past, but what about the future.

You will find some 2 cycle oils now that say they are a synthetic blend.   Just what does that mean?  What percentage of synthetic is mixed with the standard petroleum oils?  They are probably better than the standard oils, but how much?  How close are they to the true synthetic oils?

Most all normal 2 cycle outboards today are recommended at a mix of 50-1.  That is 50 parts gasoline - and 1 part TC-W3 oil.  This standard was set however when there was no synthetic oil on the market. 

There appear to be at least two on the market, (1) (AMSOL Saber brand) marine 2 cycle synthetic oil that is recommended at 100-1 where they say it produces less contaminates.   I would hope so.  The cost is about double that of the standard oils, but the benefits could be worth looking into especially for the trolling motors.

Amsoil synthetic outboard oil with a recommendation of 100-1   Pennzoil Marine 100% synthetic Pennzoil Marine synthetic blend

(2) (Pennzoil Marine, 100% synthetic 2 cycle) appears to be a more economy oil at about $30 a gallon is usually stocked at West Marine and many Wal-Mart stores.  From what I read off the bottle, Pennzoil does not really toot it's own horn & this does not really inform the boating public well.   And going on their website does not expand your knowledge much either.  I have not had the chance yet to talk to a knowledgeable salesman, but the price seems to be less than and easier to obtain than the Amsol brand.

(3)  Pennzoil synthetic blend TCW-3 oils appear to be made in 2 different grades, the higher grade labeled XLF for about $18 a gallon as compared to the Premium Plus at $12.

I did find this;  "Pennzoil Marine brings to market a marine motor oil designed specifically to keep performance-robbing carbon deposits from forming in the combustion chamber, piston tops and under crowns and piston combustion rings.   It also helps keep exhaust ports clean and protects against piston scuffing and wear on older-model engines.

Pennzoil's XLF Outboard two-cycle motor oil  was developed for engines more than a couple of years old, but the formulation makes it suitable for new high-displacement/horsepower carbureted or direct-injected outboards. "

I am sure that there are other oil companies who have good products on the market if you look far enough.

Also somewhere recently, I stumbled onto where it said that for automotive oils, the oil company can have no less than 30% synthetic in their synthetic blend oils.

Mixing Gas & Oils :   As mentioned above, the oil needs to be mixed with the gasoline for any 2 cycle motor.  There are numerous methods, with the latest being a Variable ratio oil injection (VRO).  These utilize a separate oil reservoir, or two, whereby the larger situated away from the motor pumps oil (on demand thru a sensor) into a smaller one on the motor, which in turn is pumped into the motor, mixing into the carburetor or thru fuel injectors. 

The older way was to premix your oil with the gasoline at the proper ratio.  This posses no problem if you are using the 6 gallon removable tank, as you know how much gas is left either by a gauge or by using a pre-marked dipstick.

The problem comes in where you are filling a permanently mounted fuel tank in the boat, which could be up to 40 gallons.  How do you know how much oil to mix until after you have filled the tank with fuel?  Ideally the oil should be poured in prior to adding the fuel for a complete mix.  It is probably better to over-oil than to under-oil. 

For those permanently mounted tanks, probably the easiest way to add both at separate times as you know how much gasoline you have just pumped.  Knowing that one pint of oil in 6 gallons of fuel is a 50:1 ratio.  When you add fuel do it in six gallon increments, add six gallons of gasoline and then add one pint of oil.  Add six more gallons and add one pint.  You should have some idea of how much you will be needing so as you approach a full tank, then add three gallons and add 1/2 pint.  If you fail to estimate the last 3 gallons of gasoline correctly, you will only have a little bit of extra oil, which would be acceptable.   The risk of putting all oil in last, is in some boats the gas tank filler hose is not a strait shot to the tank.  If there are any bends, or if it doesn't slope downward the whole way, then the oil might sit in the tank filler pipe instead of making its way into the tank.  The result is not enough oil in your gas, which could be disastrous.

Fuel Tanks :   When adding oil to your fuel for a premix, it is best to add the oil in before you fill the tank with fuel for a better blended mix.  The problem is how do you decide how much to put in before you pure in the fuel.  This is not bad for the 3 or 6 gallon removable tanks, but a built in tank can be challenging.  You need to enough oil to not burn up the bearings internally of the motor, but not excessive that will foul the spark plugs.  It is therefore suggested that you add at least 1/2 of what you think you will need and then at the end when you then know how much fuel you added to the tank, to add the rest of your oil needed to come up to your proper ratio. 

Now, Portable boat fuel tanks sold in the USA since 01/01/2012 must be the EPA-mandated "self-venting" design instead of the previous version with a screw-type vent in the cap.  These new replacement tanks AND new motors made after this mandate have created a problem.  It is the governmental answer to a problem that did not exist.

The new tanks have a vacuum valve in the tank so manual venting is not required.  However if the tank is used basically as a spare/emergency tank and in warm weather the fuel expands, this new valve system only opens when the motor sucks a vacuum and does not allow internal pressure to escape.  What happens then is that the pressure builds during hot weather to where it then blows fuel out around the quick coupler O-Ring seal on the tank's coupler if the hose is connected. 

To overcome this insane Government idea that will save the planet for the small amount of fuel fumes escaping from all those portable tanks being vented at the same time during boating season, and to keep the fuel from being spilled (which will cause more harm than the fumes) about the only way is to modify the filler cap of these new tanks.  Remove it and pry the inner and outer cap apart, remove the check valve and drill a small hole (about 1/16") through it.   This allows you to revert back to a vented tank.  Yes, I Know, but "Unintended consequences of well intended acts" seems to be the norm with any Government ran program.  Then when they realize they have created a problem, they come up with a new tank coupler system (Universal Sprayless Connector) that of course does not mate with anything else that has been used in the past.

This system also overflows into other uses of fuel containers for lawnmowers and chain  saws.  Gone are the days of a simple 5 gallon fuel tank with a screw on spout and cap.

Gearcase Oils ;   The same debate as for 2 cycle oil somewhat carries over into gearcase oil.   Here I have to vote in favor of the synthetic over the standard in that the synthetics are slipperier and therefore should give you better lubrication on the gears.  For those of you who are not a outboard mechanic, outboard gearboxes have all the gears revolving all the time the motor is running,  just that the sliding clutch dog engages either the forward or reverse when the shifter lever is moved in the desires location.  This essentially agitates the gear oil almost twice as much.

To tell which oil is in the gearbox, if it has not been left there forever, usually the standard oils will be a more golden color, while the synthetics will be a bluish color.  The synthetic usually also has a distinctive smell.

This started out to be an informational article, but it seems that I have about as many questions now than I have supplied answers for.


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Originally started 02-02-2007, Last Updated 01-16-2015
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