Author Topic: Idle speed recommendation for extended periods?  (Read 3792 times)

Lonne Mays

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Idle speed recommendation for extended periods?
« on: November 29, 2019, 05:49:24 PM »
I know that idling at the normal idle speed (e.g. 750rpm) for periods longer than 5 minutes is not recommended for my Cat 3126.  But is it ok to set the idle at 1000 rpm (via my cruise control) when sitting for 20 minutes or so?  Or is there another rpm I should set it to when wanting to keep the engine running while parked? 

Chuck Jackson

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Re: Idle speed recommendation for extended periods?
« Reply #1 on: November 29, 2019, 07:01:15 PM »
My coach and my Ram truck have a fast idle feature and I believe it is just under 1000 rpm for both.
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Steve Huber Co-Admin

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Re: Idle speed recommendation for extended periods?
« Reply #2 on: November 29, 2019, 08:19:20 PM »
Lonne,
Goggle "Why you should not idle your CAT Engine". There is a video from CAT that explains issues. Recommends a slightly higher rpm to load engine but doesn't specify one.
steve
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2015-          07 Contessa Bayshore C9,  400 hp
2013-2015: 00 Marquis Tourmaline, C12, 425 hp
2005-2013: 01 Contessa Naples, 3126B, 330 hp
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Mike Shumack

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Re: Idle speed recommendation for extended periods?
« Reply #3 on: November 29, 2019, 11:23:40 PM »
From the CAT Operation manual:

Lonne Mays

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Re: Idle speed recommendation for extended periods?
« Reply #4 on: November 30, 2019, 12:54:38 AM »
Thanks Steve, Thanks Mike,
From now on when we pull into a rest stop to walk the dog and stretch our legs, I'll stop the engine after I let it idle a couple of minutes.  I know that one is not supposed to shut down a hot engine until it has been allowed to idle a couple of minutes to cool down and stabilize the temperature.  And now I know that you are not supposed to let it idle for more than five minutes.  So I guess that there is really only a two or three minute window between letting the engine idle enough to cool down after driving on the interstate, and not letting the engine idle so long that carbon starts depositing in the cylinder heads and/or "fuel slobber" starts to form.  Seems problematic for getting stuck in slow moving traffic during road construction. I have encountered road construction delays where the flagger will stop the traffic for 20 minutes or more before allowing the traffic to move again.  Should we be shutting the engine down in these situations?  Or just setting it to a fast idle?
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Mike Shumack

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Re: Idle speed recommendation for extended periods?
« Reply #5 on: November 30, 2019, 12:16:51 PM »
I would not shut off engine if in traffic. What if the engine didn't start again for some reason. The mob scene would be on the six o'clock news.  ;D

Lonne Mays

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Re: Idle speed recommendation for extended periods?
« Reply #6 on: November 30, 2019, 02:04:58 PM »
Hi Mike,
Yes, this is exactly why I keep the engine idling in situations where I am in the middle of traffic; one does not want to taunt Murphy's Law, after all!  So, my question remains: what idle speed should I use for these situations?  I'm thinking I will set it for 1200 rpm as a high idle, just to be on the safe side.  (I don't want carbon build-up or slobber.)  Anyone have an idea how quickly the carbon build-up problem occurs?  Does this only happen after years of bad-idle practice, or does engine damage happen in the first trip or two that one has let the engine idle for 20 minutes or more a few times?  (Seems like if it was this immediate a threat to engine health, there would be more prominent warnings in the owner's manuals, et cetera.)  Maybe Dave Atherton has an opinion or suggestion? 
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Mike Shumack

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Re: Idle speed recommendation for extended periods?
« Reply #7 on: November 30, 2019, 02:58:12 PM »
Here's a video on the subject you may find interesting.
https://www.youtube.com/watch?v=hvfMal5fReA
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Steve Huber Co-Admin

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Re: Idle speed recommendation for extended periods?
« Reply #8 on: December 03, 2019, 03:52:06 PM »
Just a reminder to Forum members. Adept Ape is not sanctioned by CAT so following the advice in their utube videos is at your risk. The info provided on engine idleing is correct, but note that the piston used to demonstrate the issue was from a CAT 3208 circa 1960s.  It is a mechanical engine with 2 ring pistons and injection pressures in the 450-600 PSI range. The electronic engines most of us run (3126 and later) have 3 ring pistons and run from 23500 up to 35000 PSI. It didn't make any difference in this specific case, but again, be aware of the possible downsides. CAT has a number of videos available, including one on extended idleing so consider checking them out also.
Steve
Steve
2015-          07 Contessa Bayshore C9,  400 hp
2013-2015: 00 Marquis Tourmaline, C12, 425 hp
2005-2013: 01 Contessa Naples, 3126B, 330 hp
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