Here we go again, another oil discussion. This seems to raise it's head about every six to eight weeks or so. . .
Detroit Diesel has very specific oil recommendations for the two-stroke 8V71 engine, and one of them is DO NOT use MULTI-WEIGHT oil. DD calls for straight 40 wt, API class CF-2, 1% or less sulfated ash oil in the two-strokes. The Amsoil you want to use does not meet the "straight 40wt" specs - it's a multi-weight. As to whether or not it meets the rest of DD's specs is suspect, as they give no data on their website, nor do they respond to questions submitted regarding their oil specs. BTDT.
Suggest you go to and print out DD's specs, here's the link:
Other DD spec guides are available here:
Currently, the most commonly found and used oils for our two-stroke Detroits (71s and 92s) are:
Citgo Citgard Transit Low Ash
You cannot ususally find these on your WalMart shelf, they often have to be ordered from a local fuel distributor. Most come in gallon jugs, six jugs per case. You need two cases just for one oil change, as the 8V71 takes seven gallons, including the filter. If you need help finding a distributor, check the manufacturer's websites, as most have "dealer locator" links. Or drop me a note and I'll share them with you.
Royal Purple Synthetics have been mentioned and used by several busnuts, and they do have a straight 40 wt that meets DD's specs. For more info, here's the link:
Lots of folk have used synthetics in the transmission and rear axle with good results, but not so in the engine.
It's your coach, your engine, and your $$$. It's up to you to decide whether or not Detroit's recommendations are to be followed.