Big problem!! Any diesel motor will run off of even straight WVO. the problem comes with the llife span of the engine. If you don't take the glycerin out (make bio diesel) or prepare it for a clean burn (heated WVO) then your going to shorten the life of the engine. The glycerin will eventually gum inside the cylinders, sticking rings and coking the injector tips. It is not worth it.

I can understand doing it with and old mercedes and running it until it just dies. Then get another one. But for my needs that isn't the case.