I've ran M1 on my race car... Its held up well. But, I've also switched over to running diesel oil in it- 15w40 HD oil.
HD oil is great- I'd run it in everything. Problem is the fuel economy- most engines are not designed to run that thick an oil. Our older trucks will do ok- but newer vehicles call for 5w30 and thinner weights.
I dont know if they reforumulated the HD diesel ones to have that CJ4 stuff, but.. the older stuff had PLENTY of add packs. plenty of zinc. Good stuff.
pookster- as of january 1, 2007, the diesel oils have to manufactured to CJ4 specs - IE: reduced zinc, phosphorus, sulfur, etc..
the previous diesel oil spec, CI - 4 had more of these additives, and can still be found out there.. the key is to check the labels, to know what you're getting..
the big issue is the film strength of the oil,and the ability of an oil to hang onto its additive package, and that has to do with the oils ability to deal with combustion temps, which is determined by the amount of heat the oil can absorb..
generally, synthetics are better than mineral oils at absorbing heat, but the issue is, anything can be called a synthetic nowadays.. it's become a marketing term, so you can end up paying big bucks for something not much better than the buck a quart generic oil..
I've said all this to say that reading labels is key - you can find diesel oils with an SM rating, or buy a 5/20 weight energy conserving oil, and all that happens is the combustion temps cook out whatever additive packs are in there, and the stuff is just pumping thru the engine like water, not really reducing wear anymore..
the big key is that with these newer oils,the oil makers are held to certain specifications for their products, and making your engine last a million miles isn't one of them. much protection has been sacrificed in the name of higher mileage and reduced emissions.
