What kind of oil is recommended?

Ester-based synthetic formulated for motorcycles with a wet clutch.



10W40 from colder-n-a-welldigger's-butt to kinda-hot.

20W50 from watt-wunnerful-whether-wee-bin-havin to hotter-n-hades.



None of that desulfered dino base fake synthetic or oil for semis trucks.

uktw125 said:

Don't outboards run quite cool because they never heat up the coolant, the water is constantly renewed from the sea, and they don't have wet cluches.

Stick with motorcycle specific oil.

I am only thinking aloud, so someone put me right if I'm talking nonsense.

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Correct. Over the past few years oils have become extermely specialized. There are a dozen or more different Mobil 1 oils for different types of vehicles. Same goes for Rotella, none of which I'd use in a motorcycle any more. Castrol Racing 4T Motorcycle Oil is not equivalent to Mobil 1 Racing 4T Motorcycle Oil, either, as it is dino-based "synthetic" rather than ester-based based synthetic. API classifications are no longer backwards compatible, as builders of race engines with flat tappets can assert--many damaged cams from improper lube properties of "Low Emission" oils that no longer contain extrme pressure additives since they are not necessary for engines with roller followers. Extreme pressure additives are becoming so small a part of some oils' additive packages many older vehicles are carted off to junkyards due to cam failure. Many wet clutches succumb to slippery additives in "Energy Conserving" oils. Only ester-based true synthetics can meet the new "Energy Conserving" and "Low Emission" requirements and still work in TWs.