RPMs when towing

[Caveman]

What kind of RPMs do you see when towing? at what speed?

Do you tow with overdrive on or off?

What's the safest maximum weight to tow with overdrive on?



I just towed my first decent size trailer(~8000lbs). I put the trans in tow/haul mode. At 65MPH I see 2400-2450 RPMS. At this speed without overdrive I have good EGTs(850 - 1100), 170-190degree trans temp, just a fraction past halfway to the hot side on the coolant temp and crappy mileage. I get up and down hills no problem.



On the flip side with overdrive I have worse EGTs(1050 - 1200), equal trans and coolant temps and gas mileage is better at 11MPG. I can run faster(70 - 75MPH), but I must hit the tow/haul button on large hills.



So, what's best for the longevity of the truck?

 

[TRAMPLINEMAN]

Caveman, take the last zero off all your EGT temps and I'll feel alot better.

 

[OTRPU]

For my money. . . I start backing out if I'm getting anywhere near 1,200. You heatsoak those pistons to 1,250 you'll make liquid out of a solid. I've seen it and it ain't pretty. I'm gettin older now. . . tired of buyin all those parts. Not the least bit interested in going better than 60 uphills with a load. All I do is sit and wait to get unloaded at the other end anyway. I opt for 3rd and 2,000 revs. JMHO



Cheers,

Steve J

 

[MMeier]

Lil' bit off topic, but... . Steve how many miles you got showing on that thing now ?

 

[OTRPU]

She's sittin in Great Falls, MT. Last log entry shows 425,434. I'm sittin in Lakewood, CO. . . waiten for um to get a rear axle in it. Unplanned time off is killin me.



Cheers,

Steve J

 

[MMeier]

That bites, if it ain't one thing, its something else. Hope you get up and running again real soon !!

 

[Caveman]

Seems I got a little carried away with zeros on my original post. I fixed it now.



I don't really hit 1200 for long. Overdrive and 70 runs 1050 to 1100 most of the time. In third I run down to 800 consistently. It just makes me a little nervous running 2200 to 2400 RPMS for an extended length of time.

 

[Joe G.]

It just makes me a little nervous running 2200 to 2400 RPMS for an extended length of time.

Don't let that worry you. From what I've read these engines were designed for constant operation at 2400 RPM. Keep it turned up and the EGT down. Marine diesels run WOT for hours (sometimes days) with no problems.