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Discussion Starter · #1 ·
I picked up an 06' 5.9 6 spped the other day. This is my 1st diesel. I read the owners manual last night and now I have a few questions.
1) it talked about downshifting or using the gears for down grades but to be careful not to over spin the motor. No where in the manual does it say at what point does over spin become a concern, as far as RPM's.

2) What is the average rpm's for these trucks running at freeway speeds 65-80 mph? My truck is clickin about 2300 rpm, is that too fast?
 

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as far as over sinning the motor I think they are talking about down shifting and redlining the motor. diesel's as you know dont have a lot of RPM's behind them so if your on the freeway or something just dig a little deeper in the gas pedal instead of down shifting and jumpin on it, like a gasser.

I have an 05 with the manual tranny and I dont think my truck will even get to 80mph, it depends on what gears the truck has outback.
 

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Bearpaw, you don't want to exceed 3200 RPM (where red line begins) the motor will actually take more but that is the "safe threashold" that has been set. The '06 manual trans is geared for pulling. When unloaded I hate driving the interstate because of the high rpm's but when I have my camper in tow....all is well in the world. My truck is spinning around 2400 rpm at 75 mph.
 

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Discussion Starter · #4 ·
I just want to make sure that when I'm on a long trip running empty that running rpm's at 2300-2400 isn't going to hurt the truck at all.

Our company work trucks are auto trans and they run at about 1900 rps at freeway speeds so listening to the cummins run at 2300 sounds likes it's running too fast.
 

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BearPaw said:
I just want to make sure that when I'm on a long trip running empty that running rpm's at 2300-2400 isn't going to hurt the truck at all.

Our company work trucks are auto trans and they run at about 1900 rps at freeway speeds so listening to the cummins run at 2300 sounds likes it's running too fast.
i hear ya man i hate the rpms at 70-75 mph i wish i had another gear and i always thought it would be ok to have a higher low gear and so on up through the gears but after getting my new camper im glad i got that low of a gear for stopping and going on hills

we need 7 gears lol
 

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Discussion Starter · #6 ·
I guess 2400 rpm's are fine. I was driving one of our work trucks today and guess what. 2400 rpms at 75 mph. Also reading the manual tonight about maintanance it puts you in "B" schedule if you run high (2900) rpms, for extendend perionds. 2400 doesn't seem so high after all.
 

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From everything I have read, the 5.9 Cummins engine was designed to run at 2700-2800 rpm's all day long. So far I have 47000 miles on mine and I run 5 -7 miles over the posted speed limit on the interstate. In SC there are sections that are posted at 70 so I run 75-77. I don't beleive it hurts a thing besides fuel economy to run those speeds.
 

· Joe E
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lift it and throw on some 37-39"s. I run all day at 85mph turning 2K. lol.

Only problem is I find myself driving too fast alot of the time because Im use to driving using the rpm to determine my crusing speed. Old mustang gt days. The cummins purs between 1800-200 rpms.
Joe E.
 

· Dodgezilla
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Yes you can run it at that RPM but your mileage will be in the crapper. You will probably see a max of 18-19 mpg at that RPM. I tested mine once at 60mph which was around 1850 rpms. My mileage jumped up to 23mpg. Who the heck can drive that slow though.....
You could run your CTD at 3200rpms all day long without hurting anything but your wallet......
 
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