rpm

[dmrstump]

bought a 1990 thomas 18 pass with 6.2 diesel . runs 3000 to 3500 rpm at 55 mph is this normal? Tranny a 400

[bus-bro]

You're probably on your governor limit at 55 mph. That 3500 rpm is probably about max for your engine, unless you know how to turn up the governor ( & destroy the engine). My cat3208 max=2800. Those cummins & international about 2200. Smaller engines, though, can turn higher r's.

[Tango]

I would definitely check the manufacturers rpm specs on that engine. Very few diesels were ever designed to run that high. My old engine was a Detroit 6V53 "Screamer" ...one of the loudest, highest rpm diesel engines ever built...and it was redlined at about 3500 as I recall, and that was not an engine speed to be held for long. And if that is what it reads when cruising the highway, do check to make sure the tranny is shifting into high gear.

I would also suggest finding out what the tranny's final ratio is, then the rear end. Those along with the tire height will allow you to do all the calculations for speed vs. rpm. There are several online calculators that will do all the math just by plugging in those numbers.