gsxr,

I use a ton of the Chevron Delo-400 (15W-40) in my 12 valve Dodge Cummins Turbo diesel. Every 3000 miles it gets a fresh 11 quarts. Delo 400 is the only oil I've used in this truck.

I had been using Castrol 15W-40 in my MB E300 Diesel until I only recently switched to Pennzoil 15W-40, mainly because its much easier to find (WalMart). You don't seem too fond of Castrol. Why??

Deep down I kinda feel that there's not a lot of difference between brands assuming you're staying with the same weights and SAE/API classifications for comparison purposes. But, then, I am pretty brand loyal when push comes to shove.

I did check some 20W-50 I had out in the garage. (Castrol for my son's 88 BMW 325i) and some 10W-30 (Quaker State) and some straight 30 weight (Pennzoil). The API classificaion was SL only. No CJ, CH, CG, et al which is what the diesel engines usually call for. Obviously this (Castrol 20W-50) would not meet the spec for my E300D. Don't know why my independent MB garage guy was so sure to use 20W-50 in my vehicle. (He seems to be a sharp enough fellow.)