kendall 15w40 super-D3 is now syn. for great price.....

Rotella Synthetic 5/40 "blue" bottle
I pay approx $23.00 per gallon at Advanced auto and Murray's

try ''walmart'' house brand 15-40w,i saw on a diesel xm show it has better additives then mobil delvac,ive used it 2 last oil changes and it seem fine

rotella t 15/40... and beat on the diesel with over 600hp for 86k miles no troubles.

Whale oil suits best for US engines ;)

If you change your oil every 5000+ or Higher miles,what about fuel dilution to the oil,combustion blowby contamination in the oil?