"So much second guessing of th
"So much second guessing of the recommendations of the guys who designed and built these motors.
Just about every outboard out there, built from the mid-60's on, that is water cooled and runs on mixed gas should be mixed at 50:1 with regular unleaded and TCW3 rated Marine 2 stroke oil.
Older engines had neither the bearing design nor quality (in most cases) to run at that ratio, that's why there are 24:1, 16:1, 40:1 recommendations from those builders for their particular motors.
TCW3 Marine oil completely burns up at a lower tempurature compared to other oils. It is designed to burn as completely as possible in a water cooled motor, minimizing (however badly) it's affect on the environment among other things.
You shouldn't run TCW3 in air-cooled outboards because they run "hotter" and the oil would burn up before all it's protective use has done it's job. That's why they call for 30 weight oil, or now, modern 2 stroke oil such as used in lawnmowers and chainsaws.
Yes, Yamaha has been successful in producing a powerhead that will run fine on 100:1 mix. Omc thought they had it, but after two years issued a bulletin stating that all motors rated for 100:1 should instead run 50:1 unless they met an unrealistic set of conditions.
The mix rate on more modern engines is variable, but that has more to do with advances in the delivery system. The VRO was designed to mix at varied rates, less oil at idle, more at higher rpms.
Could you put that system on an earlier model - sure you could. 80:1 is fine in a 1969 motor as long as it does nothing more than idle.
Unfortunately since they were not equipped with a varible oiler I guess you could carry two tanks of gas mixed differently - one for idle and then switch when you wanted to open her up, mixed at 50:1.
EFI and DFI engines inject their oil right at the intake. The EFI (premixes) just before the lower crankcase and in the case of the DFI, the gas/oil never mix at all.
Using a computer to control the oil system, builders now have built engines that can run on a (mix) of as little as 400:1 at idle (Merc Optimax specs).
Again though, that has significantly more to do with the precision of the delivery system and the ability to get the oil where it's needed, than the quality of the oil, although to be fair, they do require oil refined for direct injected engines.
So you can accept the hype of certain oil brands that claim you can do this or that, but personally, I am going to follow the directions from the guys who built my engines.
And if they say 50:1, that's what I'm mixing at and I don't care if I'm using dino-oil, semi or fully sythetic or some snake oil brand that was refined using future technology...."
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