It CAN'T be mixed? Or shouldn't be mixed? To me, if someone says "can't", that means it will in some manner hurt the engine (in this case). This is assuming they're both the proper oils for the application. I guess I hadn't heard of 2 oils that couldn't be mixed without hurting an engine. That's going to make it real tough for having mutiple engines until all of them get the same oil in them. | 
JD Plus-50 II oil
