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Why can't our diesel's idle?

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I've been reading that the Cummins engines in our trucks, when idling in cold weather, get buildup in the cylinders from an incomplete fuel burn; causing all kinds of mayhem in the motor. I was curious as to what's different with these engines? I ask this since all the other diesel engines I'm around on a daily basis (pulp truck , skidder, excavator, ect) will run all day long, with lots of idling in that time span, and yet it doesn't seem to bother them any? Looking for some clarification.

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With the 4 valves per cylinder you get alot of air flow going, mine will drop the temperature at idle in frigid temps. All that air causes cooling in the cylinders. I had Cummins speed up the PTO idle so that I could run my engine at a high idle if I want.

Its not actually good for any diesel to idle in cold temps, always best to elevate the idle some how. Its not a cummins issue I have seen about every engine mfg have slobbering issues with excessive cold idle time.

  • Owner

Yeap... Flman is right... The extra 2 valves tend to drop the combustion temps rapidily like at -20*F my pyro might show barely 200*F idling with 190*F worth of coolant. Yes my probe is pre-turbo. But at around 400*F which happens to be the flash point of the tar build up you start to either collect it because the cylinder temps are to cold or burn it off because you got it hot enough. Like my wood stove is really simular to the Cummins if I choke the air down to about 400*F the tar starts to build up on the stove walls and pipe walls. Then once you heat it up you burn all the trash out. Maybe that why I got a pyro on my stove... :lmao2:

  • Author

Thanks for the replies and clearing that up. It just struck me as odd that all of our equipment idles so much and then to read that it's bad for the motor. Guess I'll bump up the idle to make em rev more, still learning about how diesels work!

only way to make our trucks high idle is to either smarty flash it, or get a dealer to do it, and to get it to go on command, you have to have several different switches to fool the ECM....Mopar1973Man knows how to do it or, you could always do what the 12 valve guys do and find a high idle stick to jamb to the pedal a lil bit past idle....aka the high idle stick

  • Owner

only way to make our trucks high idle is to either smarty flash it, or get a dealer to do it, and to get it to go on command, you have to have several different switches to fool the ECM....Mopar1973Man knows how to do it

Right here...

http://mopar.mopar1973man.com/cummins/2ndgen24v/high-idle/high-idle.htm

or, you could always do what the 12 valve guys do and find a high idle stick to jamb to the pedal a lil bit past idle....aka the high idle stick

Like I found out high idle alone does do a whole lot for heat... Read the addition info on the bottom of the page on the link above...

I got my dealer to unlock the high idle and then i built the fooler (as my sig says). Been well worth it:thumbup2:

On this subject; has anyone tried a manually operated "high idle" cable, and for that matter, are there any out there that were purpose designed for the 2nd.gen application? Maybe I'm not looking in the right place, but I have not found any. A few generic twist lock cables are available, but you have to fabricate your own brackets and such to attach to your pump.

I just have like a choke knob hooked to the pedal. I pull it out until it's where I want.. I would do that high idle version 2 thing, but I don't know if I would get the results I like out of it. If I calibrated it to 1000rpm when it's warm, then it might only be running 600rpm when it's 20f.. Vice versa it would warm up and be running 1300rpm when I went out to it.. Yes, having no computer sucks lol.

  • Author

Yeah right now I'm rocking the "high idle stick", or more precisely, the "high idle scraper" lol I would like to get the high idle flash done as well as an exhaust brake as I've seen that that does wonders as far as warm up times. Unfortunately all this costs money!

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