Untangling the  2 Cycle Fuel   to Gas Ratio Mystery

   Let's take a look at why 2 cycle motors need a fuel oil mix.  On a 4 stroke motor (most automobiles and late outboards) the internal lubrication is done from a oil reservoir pan, where a mechanical oil pump pushes oil up to all working parts of the motor for lubrication.  A 2 cycle motor being more compact, does not have this reservoir, so it needs a different form of internal lubrication.  This is accomplished by mixing oil in with the motor's gasoline fuel. 

    This ratio varies greatly depending on the construction of the internal parts, mainly the connecting rod bearings.   Early on the connecting rod (the part that connects the piston to the crankshaft) bearings were simply just the bottom of the aluminum rod.  This was fine for low RPM motors, where here the recommended mix would have been 1 part oil to 12 parts gas.  (If this doesn't make sense, wait till farther down for a better description).  This ration was leaned out as better bearings were developed (like bronze cast in inserts)  to 16 or 24 to 1 ratios.  When needle roller rod bearings came into being the ratio was changed to 50-1.  This was a blessing to those who used their motors only for trolling where the spark plug fouling was prolonged (because of the excess unburned oil).  Later some manufacturers installed an oil reservoir and designed a oil pump that varied the output depending on the RPM of the motor, thereby eliminating the fuel mixed gas. 

     Due to the nature of two-stroke marine engines, two-stroke oil lubricates the engine parts as it passes through the engine and is then burned along with the fuel.  Two-stroke oil is either physically mixed with the fuel or, in the case of direct fuel injection, is combined with the fuel in the combustion chamber.  This is in contrast to four-stroke engines which have oil sumps circulate the oil by pumping it throughout the engines.

   The long-term objectives of the two-stroke engine industry have been to reduce emissions which contain burned and unburned oil that have 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. 

    How This Relates to Antique/Classic Outboards :  Many of these older motors also did not have good crankshaft seals as we know in modern times.  And these manufacturers many times recommended using SAE 40 weight automotive oil.  They simply used the thicker oil as a seal around the crankshaft main bearings.    

   Typically most 2 cycle outboard motors made after about 1970 will use a recommended fuel to oil ratio of 50-1 (3 ounces of oil to 1 gallon of gas or 13 ounces of oil to 5 gallons of fuel).  This year distinction may vary with manufacturers.  The reason is on the style of the internal bearings being used in the motor.  As mentioned above, the older smaller motors may have used only just the aluminum rod or bronze bushings/bearings, which required better lubrication than the newer hardened steel needle style roller bearings.

   The issue is with the richer oil (lower ratio), the motor usually can not effectively burn all that oil and will smoke a lot, even leave a oily film on the water behind it.  And if used mostly for fishing, where trolling for long periods of time, will eventually foul the spark plugs, making the motor eventually die.  For many years fishermen (me included) always carried a small tool box with wrenches and spare spark plugs.  

     In early years the motor operating instructions were written in parts of a pint to one gallon of gas, like 1/3rd pint to 1 gallon, which can be confusing if you try to convert to ounces.   Currently, and for a number of years, outboard motor oils (if in quart plastic bottles) will have a clear strip on one side of the bottle that gives markings as to how much oil is left (in ounces).  FYI, 1 gallon = 128 oz, 1 quart = 32 oz,  1 pint = 16 oz.

     It has been standard in the industry to write the recommended ratio as, say 24 to1, 32-1 or 50-1.  However this is rather confusing to some, as it is comparing apples to water melons, and it seems to be written backwards.  It would have been easier/more accurate to say 128 to 24 instead of 24-1, (better yet 24 to 128) The oil ratio is constant where the gas ratio is what changes.  In reality, when mixing this fuel, the gallons of gas is usually the known factor while the a mount of oil added is what is in question.  Therefore we usually have to figure the amount of oil backwards (by knowing or guessing the amount of gas needed) to arrive at the desired amount of oil.  In mixing in a known can/tank sizes that are removable, it is simpler.  Where the question comes into play is those boat with built in fuel  tanks.  Here it is best to pour the oil in first so that it mixes better with the gas as the gas is added.  The proper method of refueling is listed farther below.
  This chart below gives the operator a pretty precise amount of oil to be mixed into a known fuel can/tank.  Here the yellow highlighted column is for the later 50-1 motors.  Again this is all confusing as you have to know the amount of gas needed to arrive at the needed amount of oil.  Therefore it really should have been 1-50 (one part oil to 50 parts gas).  But how do you buck a long time tradition.

    From 1985 to 1988, in an apparent effort to create a more environmentally friendly atmosphere for boaters, (driven  by Federal regulations) OMC actually recommended a 100 -1 mix, this was written on a decal placed on motors of these years.  Observed on one 1986 6hp, 1985 9.9hp and the 1988 Evinrude 15hp, there was a decal sticker on the powerhead cover next to the fuel line connection which shows cartoon icons of a fuel pump, and oil drop, showing a ratio of 100 -1 for the fuel to oil ratio (as seen in the header photo).

   Apparently this effort created some problems with some motor users (probably higher HP than what we are referring to here) so OMC issued a Technical Bulletin  #2162 dated March 1986, for the mechanics to remove the 100:1 decal, replace it with a new 50:1 decal and inform the owner of the consequences, when the motor was serviced in an OMC repair shop.  This was recommended for rental, commercial and heavy duty service engines. 
 

   The factory apparently did replace some damaged power-heads because of this.  Apparently 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 up due to lack of adequate internal lubrication.  There was another bulletin sent out in September of 1988 that kind of soft pedals around the issue, for a link to this bulletin #2211 CLICK HERE.  

    Back when OMC re-introduced their 50:1 ratio of oil, an old time marine mechanic was told by factory engineers that their motors would survive on 100:1, BUT the problem was that they couldn't trust people to measure the proper amount of gas/ratio accurately or control the amount of oil they used.   So they reverted back to 50:1 ratio as a safe haven. 
 

    The 100 -1 was sufficient lubrication for most motors while running.   The bulletin had nothing to do with lubrication while running and everything to do with storage of the motor (again legal talk so to not get involved in a major recall).
 

   So reverting back to the 50 -1 gave boaters a margin of safety in case of a lean carburetor on a multi carburetor motor or an overheat and it can still protect the clean internal parts while not used for a few months in a climate that can create internal sweating.   It appears that the manufacturer's lawyers were very careful to not create the situation where a possible class action lawsuit could not be presented, so they emphasized the storage internal lubrication theory where the average boater could not dispute it.
 

   Any lack of the proper oil ratio could very well be due to those larger boats that had internal fuel tanks where upon refilling, the owner may not have been accurately mixing the oil in a ratio to the fuel added.  The oil should be added to the tank before the fuel is added to ensure adequate mixing of the oil.  But on these built in larger tanks and an unknown amount of fuel needed prior to refueling it is very hard to be consistent from each refueling to another.  And I seriously doubt that the majority of the fuel gauges on boats really read right, or that the owners even know the tank capacity to start with.   When I got my latest boat the gas tank was VERY near empty, I added a gallon of gas at a time, and recorded the fuel gauge setting, so I have a pretty good idea of what the gauge said to what I actually had in the tank.

   The proper way to mix is to pour the oil in first, then the fuel, which gives you a more complete mix as compared to just adding the oil after you top off your tank.   Therefore in those cases, the only real way to be sure is to use known 5 or 6  gallon cans and add the right amount of oil before you add the gasoline, then transfer into the boat's tank.  Or if at a fuel dock or gas station, ESTIMATE the amount of fuel you may be needing, then pour in your oil into the tank.  Finish the refueling and then add the minimal amount of oil needed to meet the required mix ratio.  If you overestimated, no big deal, as no harm done, where underestimating could be devastating.

   This management/public embarrassment is probably what led to the development of the newer oil injection directly into the larger motors.  Some were called VRO (Variable Ratio Oil  injection), meaning depending on the RPM of the motor, the ratio of oil being injected into the motor was at a different rate, (likely 100-1 for slow speed  and 50-1 at high speed).  This somewhat solved the initial problem problem of accurately  mixing the oil into the fuel, until you may have had a malfunction, or blockage in the injector line and get no or minimal oil injected.

   On the smaller hp motors that we are dealing with here that use portable fuel tanks, it is recommended that you can use a wooden dowel marked off in gallons by adding 1 gallon at a time to the tank, then marking the dowel at that level, therefore you can accurately measure and can add the proper amount of oil to what fuel you add, there is usually no problem.

   Now with the TC-WC3 outboard oils, the lubrication is way better than with the oils available even in 1988.  The OMC factory engineering/service department has researched and said that the AVERAGE outboard will be used only about 15 hours a year according to one of their studies.  However there is documented usage of a 1988 6 hp Johnson purchased new and being used a estimated total of 1200 -1700 hours of trolling time using the  (at that time) recommended 100:1 mix.  He uses his 70 hp as a go to motor, then the 6 hp for trolling and this 6 hp was still running fine in 2010.

   As mentioned above, the reason for mixing oil into the gasoline is that since these engines are 2 cycle, (sometimes called 2 stroke) there needs to be oil mixed into the gas to lubricate the internal parts (piston, crankshaft and bearings) of the engine, as there is no crankcase oil reservoir or oil pump as in the 4 stoke engines.

   Less oil than recommended in the fuel makes the engine run leaner and warmer (less power, causes detonation, overheating, but more important, could cause the motor to get so hot (under extended conditions) that it could seize the piston inside the cylinder walls).   More oil makes the engine run rich and fowls plugs (less power also), but forms carbon deposits and friction can increase caused by the carbon builds up, so more heat is also made.  Therefore a happy medium needs to be achieved. 

    That is where the VRO system came into being for the larger motors.  Initially it got some bad publicity, and even some old line mechanics recommended that it be disconnected and go back to the premix.  But it worked and does have a safety warning system that needs to be monitored/maintained.  Later this was basically renamed to OMS  (Oil Metering System) where it functions very similarly to the VRO pump, it is just far less variable.

   You will see considerable discussion from time to time of this fuel ratio mix on at least one of the major boating forums when related to vintage motors.  There are some that seem to be emphatic about sticking with antiquated factory recommendations even though the OIL QUALITY has dramatically increased during the last 30 years. 

   It seems that if you take a page from the new automobile manufacturers concerning recommended oil changes and apply it to outboard motors there should be a parallel where the old days it was recommended to change oil every 2500 or 3000 miles, now that has moved up to 5000 or 6000 miles.  And now most manufacturers recommend full synthetic oils.  This change pretty well has to do with better engine construction, AND the use of newer AND better oils.

   Air Cooled Outboards :  OK, we have pretty well covered the most popular (Water Cooled outboards),  but what about the Air Cooled motors?   These motors run at a higher temperature than water cooled, therefore it seems that by blindly using the TC-WC3  (Two Cycle-Water Cooled version 3) oil may be out of line.   OK, is there a approved Air Cooled oil?   Certainly, and it would be oil designed for chain saw/weed eater, leaf blowers.

    But now what would the mix ratio be?  Remember those 60/70 year old air cooled motors were not made using needle roller rod bearings as modern chain saws do, but probably simply bronze bushings throughout.   They may have needle rollers as a top main bearing, to compensate for the heavy flywheel rotation.

    Here is what I use on my old Elgin 1 1/4 and 2 hp outboards.   Yes, I use the recommended chain saw mix, BUT I also add about 1/2 that amount of SAE 30 to the mix, ALONG with a moderate amount of Sea Foam.  This SAE 30 gives my bronze bushings that heavier weight lubrication of the older days.  My reason for the Sea Foam is that I do not know the internal condition of these motors, therefore the addition of Sea Foam gives me a cleansing effect of loosening any carbon in the chamber and rings.  The addition of this can not hurt, and most likely can help greatly the internal condition of the engine.

     Storing Vintage/Antique Outboards :  OK, here we see a totally different issue.   It is known, (but not widely advertised) that modern oils (TC-WC3) being lighter are also prone to evaporation over time.  What happens internally to your stored motor, the oil internal coating disappears, and over time the motor can seize.    I have personally seen this on two small outboards that I recently purchased.   Both owners swore that their motors were not seized 2-3 years before.   One, the owner knew it and had unseized it, (but did not run it).  The other, the owner was totally unaware until he put it up for sale, and it had been stored in his unheated garage all the time.

    Both of them, I got unseized by using penetrating oil in the cylinder, using a brass rod down inside the spark plug hole, tapping the piston to get it to move, and then a breaker bar and socket on the flywheel nut.  The one I did get running, immediately after breaking it loose, it had 60# of compression.   After getting it running, the compression went up to 86#.

    From this, and doing research among other AOMC members, it is recommended that for you who collect these old motors to when you shut them down, to FOG them internally with fogging oil, AND drain any fuel out of the gas tank AND carburetor.

   Black or Gray Oil Coming Out of Upper Exhaust Vent &/or Lower Unit Holes :  Many motors are basically those used as a secondary motor, usually then as a trolling motor, which are ran for considerable length of time at a lower RPM.  The fuel oil mixture ratio of 50-1 is probably too rich for this type of usage. The black oil that seeps out of the motor is just unburned oil from the gas mixture.  The black color is coming from the carbon created during the pistons firing situation and is accumulated unburned inside the exhaust housing.  When the motor sets for a while the excess unburned oil in the fuel is mixing with and softening up the carbon, creating the black oozing oil.  You can reduce the amount somewhat by properly adjusting the carburetor idle jet to it's leanest position, also where the motor runs best at an idle, not the cure but may help. 

   This black or gray oozing oil could be also because of a stuck open thermostat which would not allow the motor to warm up.  However thermostats that get stuck usually do it in the closed position, so a bad thermostat is usually not the cause of this condition.

   Or, it could be a 6 gallon tank that the fuel line is still attached to the motor during storage while the outside ambient temperature is high enough to expand the fuel inside the tank to where the gas is forced into the carburetor and IF the carb needle valve is leaking, it will force fuel into the engine and out the exhaust which mixes with the exhaust carbon, then leaches out as BLACK oil out the prop's exhaust.  

   If you are getting a thick creamy gray oil oozing out the prop hub, it is essentially the same as above except the inside of the housing may have less carbon build up, therefore the color will be lighter.   It is the same thing as described above, but possibly from a new or rebuilt motor that may not have been run much for some time and there is not a lot of carbon inside the exhaust housing.   If there is minimal carbon built up from previous runnings, the oil will be the thick creamy light gray color that has a lot of water mixed in it.   On the 9.9/15 hp, this could also be caused by the converging ring (#332395) is missing on the prop.  This plastic ring facilitates a suction from the outside of the prop when the motor is running at a slow speed to help suck more of the exhaust gasses away from the "thru the prop exhaust" when idling in neutral or running slow.

Here black oil is running out of the upper exhaust vent of a 1992  9.9hp after the motor was used for trolling using a 75-1 ratio semi-synthetic & then sat for 3 months	Here a creamy colored oil is exiting the motor's exhaust housing.  This is basically the same concept as the black oil except probably in a cleaner motor, BUT notice the converging ring missing on this prop allowing a oil build up inside the housing

   This oil seepage may not be evident until a day or even a week after usage, then will seep out up to a couple of months later.  Most repair shops just recommend that for most boaters to then simply live with the idea that you may have to wipe it down after each usage. 

 

    You could also see this oil seeping out of the front lower unit water drain hole.

 

    It is observed that if these motors are used on a smaller boat as the only propulsion, and act as a "get there" motor and also as a trolling motor, this black residue is considerably less to almost non-existent because the motor gets hotter because of the faster RPM, on the return to the launch, where the motor has a chance to warm up, thereby "burning" some of this excess oil.

   Also if the engine was winterized with fogging oil then you would expect to see oil coming out of the exhaust because this would soften any carbony buildup in the exhaust system.   If it smells like gas  =  unburnt 2 stroke oil.   However if it smells of rotten eggs  = Lower unit oil.

    This dripping oil many times may be confused with the lower unit oil leaking because of the color and location of the oil coming out.   Another reason as to this also happening is as explained above under the Converging Ring on the prop, is if this ring is missing it can hurt by not creating enough suction to pull the oily residue out of the exhaust housing at low speeds.

    Akin to the above situation, where spark plugs have continually become fouled, I have been experimenting with using 2 gas tanks for the last eight years (2009) now and for me, I am happy with the idea.  One, a 3 gal. tank, mixed at 100-1 with full synthetic oil and it is used  ONLY FOR TROLLING, the other is the 12 gal. main 50-1 tank also used for my 1980 70hp outboard jet on the same boat.  Again, I am using the 100-1 synthetic ONLY for trolling with the 9.9.  If and when I need to run with this 9.9 motor faster, I simply switch to the larger 50-1 tank.  However the winter of 2007/2008 in an emergency flooding situation, where I was rescuing a lady and her son who were stranded in her house with the water was still coming up fast, my main 70 hp jet water intake had become plugged with floating grass or hay, making it useless.  It was getting dark and we were caught is a strong very swift current pushing me broadside along a fence, I did not have time to change the fuel tanks as I was broadside to the current, with the 9.9 then my only source of power then.  I ran this motor at full throttle during the last half of this rescue mission for probably 20 minutes before I got to dry ground and offloaded the passengers.  As of 2013, I am still using this motor with no apparent harm.  But I was using the FULL SYNTHETIC 100-1 oil mix.

   I got the above idea from the newer VRO oil injection motors.  This VRO abbreviation stands for Variable Ratio Oil injection.   The larger motors using it (not the 9.9 or 15hp however) electronically sense the different RPMs then automatically adjusted the oil injected ratio.   They put out a 50-1 ratio at high speed and a 100-1 at slow speeds.  Recently the motor manufacturers have gotten away from this VRO system and went to a direct constant ratio pump.  This apparently is because with the VRO on a large motor with multiple carburetors, if you are idling, or trolling at the lower ratio fuel mix, so you decide to pick up and run, the carburetors still has the bowl full of that low ratio mix, the engine will then be UNDER lubricated until fresh richer fuel is drawn into the carburetor.

   I have kept track of the run time at trolling with this 100-1 ratio with one particular motor over a four year period and can account for 43+ hours of only trolling, with only one a sputter, all it took to clear that up was to speed the motor up until the spark plug became un-fouled.  Then 4 hours later, back home I changed the plugs before the next run.   

 

    In 2009, I switched over to using a 75-1 ratio of a semi-synthetic oil mix with the idea of not having to worry about changing tanks, but I do get the black oily residue as seen in the photo above, so possibly back to the 100-1 full synthetic ratio for all my running.

   You will see responses on some of the major outboard motor forums being very adamant to not deviate from the factory 50-1 ratio.  I realize that many of these knowledgeable persons, (many who may be old line mechanics) who may have seen blown engines in the past which may have been attributed to poor oiling.  However oils have changed dramatically even in the past 10 years.  Others on these forums expressing their concern may be just repeating what someone else has said.  And you have to consider that anyone who posts on a public forum does not want to stick their neck out, make a recommendation only to be chastised if the results turn out negative for whatever reason.  (BEEN THERE - HAD THAT HAPPEN). That is the way of life these days where liability's head pokes itself out.  That said, I have done the tests ON MY MOTORS for a number of years, which are new enough to have needle bearings, and you have read the results above.  I am happy with what I now use, but if your situation is different, then make your own decision.

    I many times use the boat in bays which are somewhat salt water, initially I used to switch tanks to the 50-1, when I use the muffs to flush out the trolling motor at the end of the day.  The thought here is to use the richer gas to leave a better oily film inside the motor when it is stored until next time.  I now think that the full synthetic oil is so much better, that I don't bother changing, however when flushing, under these conditions, I do NOT KILL the motor with the kill button, but choke it to kill it.  This will tend to also increase the fuel/oil inside the motor if I do let it set for a while because where I live, as I normally do not fog my engines for winter storage.

 

If you try t

gray fuel line deterioration of liner