I posted this question a while back & never did get an answer, so if you guys bear with me, I'll try it again:
What is considered the max rpm for sustained highway driving with a 300 SD? What is the best rpm for mileage?

jim Peterson

I experimented with my 350 SDL on a recent trip. One tank at 75 ran just over 3000 rpm and fuel use about 24. Slowing to 70 just under 3000 fuel use went to 25. Assuming most engines are not meant to run near max for sustained periods and as Bill notes the fuel use is kind of an indicator. The A/C on with windows closed requires the same Hp as A/C off and windows open.

Around 3000rpm for most 70mph speed limit zones, which means 65-75mph.
500 miles is a safe range out of a full tank, without getting into the reserve and risking sucking up stuff at the bottom of the tank. I average 25-27 mpg.

I want to thank you guys for your comments on my RPM question, but the main thing I was looking for was: what is the max I can run. Here in Nevada, like when I'm driving Hwy 50, I sometimes will run 120 MPH & more in my Chevy powered Jag for 100 miles at a time. I was wondering how fast you can safely run a diesel for an extended period of time.
jim

I like to run my 81 300SD pretty hard. She seems to like it, she idles smoother after a hard run. My max RPM is about 4800 - 4900 and thats achieved in the L selection on the tranny. If I recall correctly she goes about 85-90 km/h ( * 0.6 for mph ). In my humble opinion if one changes the oil as recommended and other follows maintainence procedures they can run their MB diesels as hard as they want. Mileage seems to decrease at a slower rate as rpm goes up for diesels vs. gas.

I ran my 126, an 87 300SDL on cruise control at 100MPH for at least 50 miles on Allegator Alley in Florida because my radar/laser detector was poised for bears. At one section, I pushed the pedal toward the metal for a few seconds, and clocked 112MPH with a lot of pedal left.

Jim Leonard
1987 300SDL with a special radio

What special ratio are you running?

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Bart
1987 300SDL-T
1985 190E 2.3-16
1978 240D
1957 220S(running one day, I hope!)