yep, my reasoning for not mixing is not so much incompatibility...but that when people mix syn with dino they seem to want to apply the syn characteristics to the vehicle rather than knocking it down....especially on air cooled motorcycles the difference is significant in hot weather and heavy traffic whereas a dino filled bike may start losing viscosity around 220*F the syn filled bike can go up to 300*F before it is going to break down the same way......so the hot protection is greater. Some guys do the mix to save money and expect the dino to mysteriously pick up the better qualities rather than thinking of it as really just slightly better than dino. As rule of thumb if you mix them yourself.....take precautions as you would with regular dino...and the slight benefit is your emergency buffer.Both are typically fully compatable with one another (think synthetic blends). It also does not matter if you switch from one to another and back again. I do however like to use a brand/type that I have had many years of trouble free engines with (no sludge or wear problems). I understand (and may be wrong) that synthetic oil is comprised of a single sized taylor made molecule to get the viscosity desired and dino oil is a homogenized oil of various sized molecules to get the desired viscosity, this is what I understand (and again may be wrong) to be the main reason why synthetics hold up better than Dino oils.