I've the oil changed at the stealer twice now. Bought a couple of oil analysis kits from AV lube (thanks Karen :) ). On the form they ask for lubricant manufacturer. I called the stealer and asked the parts dept. what oil they used, Parts guy said bulk GM Goodrench. Also said they have two tanks one for the gassers and one for the diesels. The question is. What is GM Goodrench oil? I suspect it's purchased locally and has to meet certain specs.. Anybody have an idea? Maybe I should start doing it myself and use Shell Rottella T like I used to in my last job on a fleet.

The GM Goodwrench oil is made by Mobil. It is good oil and well within the specs.

As long as it meets the minimum specs, you're fine. Today's "minimum" specs are very good. The new CJ-4 oil is better than even the CI-4+. I can't speak for the GM oil, but I know that Rotella, Delo, Premium Blue, Tection Extra and several others are getting good reports for wear protection on the oil-guru websites for the new CJ-4.

The GM Goodwrench oil is made by Mobil. It is good oil and well within the specs.
Right, should state that on the back of the bottle label...

As indicated, if it really is Goodwrench oil, it is indeed an excellent Mobil Delvac diesel oil. However, some local GM dealers are quietly drifting away from real Goodwrench oil and purchasing lower cost/price advantage who knows what oils.. And are not putting a sign out front indicating "hey, we are now purchasing a dirt cheap oil from honest Ed's oil company".... So, buyer must beware if the oil changes are done from bulk oil at the dealer. All Goodwrench oils in bottles is indeed high quality Mobil oil, to be sure....
George Morrison, STLE CLS

And Karen thanks YOU! :-)