fuel/oil ratio opinion

[gullake]

I just finished restoration of '61 Johnson 40HP. This engine specifies a fuel/oil ratio of 25-1. In it's era it was common practice to use regular motor oil to mix with the gas. Today we have highly specialized two stroke oils to use. Would it be safe to use a leaner fuel/oil mix in an engine that originally specified 25-1? I am more concerned with dumping less oil into our lakes than I am with the cost savings. What changed in outboard motor engineering when the ratio was changed to 50-1 anyway? Anybody know.

 

[jbjennings]

Re: fuel/oil ratio opinion

If you're worried about the oil in the water, use a full synthetic tcw-III oil. It's biodegradable quicker than normal 2-stroke oil. If it says 24:1, that's what I'd stick to. However, your motor is right on the borderline of when they changed to 50:1. By reading some of the real experts posts here and elsewhere, I believe the change from 24:1 to 50:1 was made possible by using roller or needle bearings at all locations in the powerhead. Previous 24:1 motors had bushings in some places like the connecting rods/piston wristpins that needed the extra oil to keep from wearing out quickly. Some motors in the 50's had so many bushings that they even needed 16:1!
Perhaps someone here will be able to tell you if your motor has all needle and roller bearings and you would likely be safe using less oil. There's no way even if it did have all needle and ball bearings that I'd use less than a 40:1 mixture.
JMO,
JBJ

 

[JB]

Re: fuel/oil ratio opinion

I would stick to the 24:1 mix, Gullake.

If you are concerned about pollution go to a full synthetic TC-W3 oil as JBJ suggests.

 

[kenmyfam]

Re: fuel/oil ratio opinion

If in doubt then more oil is never the wrong thing to do. Very expensive to have a mix that is too lean.

 

[wbeaton]

Re: fuel/oil ratio opinion

I am not going to give a recommendation, but I will say there is no internal difference between a 1961 40 hp and a 1964. 1961 = 24:1 while 1964 = 50:1. At least you know for sure that 24:1 won't hurt anything.

 

[seahorse5]

Re: fuel/oil ratio opinion

Your particular motor has all roller and needle bearings in it, no brass bushings, thus it is OK to run today's oils in it at 50:1.