Used Oil Analysis. Shows Wear metals, Anti-wear elements, active additives., viscotity, flash point. Pick one of the few test labs, run your motor(not idle) for 20 minutes, drain, catch some oil in the midstream of drain. Put it in the bottle and container they give you, and mail it to them. They will mail and email you the results.
They will let you know if you have any water or antifreeze (Na) in the sample. They will tell you if you need to change air filters (most of the time telling you to stop using a k&n) as it supposaly lets more dirt and dust in (silicon on the report) Sodium and Silicon are no good! I am lucky to get good results with my cone k&n.
The 4.0 is known for spitting iron (i think average 30 parts per million). A lot beleive its from the timing chain, but with regular changes, it's not a problem.
"new" oils have reduced ZDDP.(800ppm)(search) SM is the new API standard . GTX is a good Dino and shows good(higher than reg.) zinc and ph levels. I run the diesel syn Rotella 5w-40. With over 1200ppm zinc and phos, its up to the task and shows.
Look on the back of the bottle, sometimes you can get lucky and find some SL stuff with the 1000ppm zddp regulation. The stuff I'm using is SL. The new dino Rotella 15-40 is cutting zinc and ph and using more Boron, as is Mobil and most other's.
