I've got 10 years running on WMO in several diesel engines and spent thousands of hours of runtime testing. Filtering doesn't work as much of the stuff you want to get out is on the order of molecular size. Various additives and metals are put into oil and for LONG TERM RUNNING these should come out. Now you can filter oil and run it for a while, I started that way. After a few hundred hours, I broke down the fuel system and started inspecting parts. I noticed a build up like on the bottom of a piston head. While I noticed no change in the engine performance, I assumed that it was only a matter of time. Now I invested a lot of time in this project and do make filters for this kind of thing. I'm not trying to span the list but here is a paper that I wrote on Waste Oil Running: http://bestcentrifuge.com/running_on_waste_oil.pdf I am happy to answer questions if something is not clear.