Mobil 1 FTW

 

Obviously you need to change your engine oil if it is dirty, no matter how many miles it has on it. Most of the dirt in your oil comes through your air filter, so if you have a cheap filter there then you will have to change your oil more frequently. As for all the Amsoil bashers, you should really do some research first.

 

I was told that you shouldn't switch over to conventional from synthetic. I only use full synthetic.