The complete story is complicated, and while some parts of the story/rumor are based on facts the whole idea is not.
First, with any E20 fuel, 20% of the fuel is ethanol which is hydroscopic, which means it is able to attract and hold water molecules from the surrounding environment. The higher the air humidity and the amount of Ethanol mixed in the fuel the more water molecules are absorbed by the fuel.
From scientific data we know that with a new engine about 1% of the moister in the fuel finds its way into the crankcase. With engines that have done 5-digit amount of kilometers that percentage can become much higher.
The idea with full-synthetic engine oil is that it would have water-dispersal additives added to the oil, which makes it easier for the water molecules to separate from the oil and speed up corrosion inside the engine. The truth is that water-dispersal additives are added to all sorts of engine oils… and I think that it’s more about the brand name about who has more or who has less water-dispersal additives added to the engine oil.
You could use engine oil that has Ester as an additive, ester helps to keep the water molecules inside the oil in check. Of course to much water messes up any engine oil…
I was told by a mechanic at my local motorcycle shop that it is not good to use full-synthetic engine oil while using PTT Bluegasohole E20 as fuel. Is this true and why is better to user regular engine oil?