The only way to really clean all the old stuff out is to change the oil to what you want, run it for a few minutes, change the oil again, run it again, and change the oil again. Changing the oil filters every time you do it as well. Not very practical to do this though so I'd recommend just making sure you let it drain good, change the oil filter, and then just don't worry about it.

 

you guys should check out www.bobistheoilguy.com

 

When you switch over to amsoil you buy and bottle of cleaner and drain a little oil out and then add the cleaner then you run your motor at like 2000 rpms for about 15 min. Then you drain the oil hot and it cleans it out. That is how asmoil has you do it. Also not sure if the dealer will switch to other stuff for you or not.