In very cold weather, should I idle until the RPM settles down? - Chevy and GMC Duramax Diesel Forum
11-16 LML Duramax Powertrain Discussion of components that are directly involved in the power production and all that is needed to get and keep the truck moving . Engine , Transmission, Etc.

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post #1 of 68 (permalink) Old 11-14-2019, 09:49 AM Thread Starter
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In very cold weather, should I idle until the RPM settles down?

I always assumed that it was good for the engine to idle for a few / couple of minutes at start-up, to let the engine RPM settle down.

Right now the temps here in South East Wi range from 17-30 deg. In the morning the truck RPM is about 850 when first started. After couple of minutes it settles down to just below 500rpm.


I am reading conflicting advice on the net, with some experts claiming idling an engine is bad. While others say idling for extended period of time is bad, but there is no definition of what entails "extended period of time", though I assume it means well more than start-up idle, so over 15 mins.


So is it good or bad to let my LML idle for a couple of minutes , until the RPM has settled down?
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post #2 of 68 (permalink) Old 11-14-2019, 11:06 AM
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Quote:
Originally Posted by Gnome View Post
I always assumed that it was good for the engine to idle for a few / couple of minutes at start-up, to let the engine RPM settle down.

Right now the temps here in South East Wi range from 17-30 deg. In the morning the truck RPM is about 850 when first started. After couple of minutes it settles down to just below 500rpm.


I am reading conflicting advice on the net, with some experts claiming idling an engine is bad. While others say idling for extended period of time is bad, but there is no definition of what entails "extended period of time", though I assume it means well more than start-up idle, so over 15 mins.


So is it good or bad to let my LML idle for a couple of minutes , until the RPM has settled down?

it comes down to what you consider idling. Do you consider a red light to be idling? Personally i have no issue remote starting my truck in the mornings, and letting it run for 10-15 minutes. The soot and carbon accumulation you'll build up from idling for a few minutes is trivial, and the warm engine with fresh warm oil pumped through it is going to be a lot happier when you hit the go pedal. Up here its not uncommon on older diesels to set them to idle for 30 minutes to get warm, though the LML's with there high idle warm up a lot faster. On the other end of the spectrum there are also slope trucks that idle for days straight, literally never being shut off. Dont worry so much about idling. Its better to let the engine be warm, lubricated, and happy, then to worry about how many minutes the truck sits idling. That said, on a emissions intact LML, idling will likely have a negative impact on regen interval, but again, insignificant in the grand scheme.
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post #3 of 68 (permalink) Old 11-14-2019, 01:14 PM
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Quote:
Originally Posted by Gnome View Post
I always assumed that it was good for the engine to idle for a few / couple of minutes at start-up, to let the engine RPM settle down.

Right now the temps here in South East Wi range from 17-30 deg. In the morning the truck RPM is about 850 when first started. After couple of minutes it settles down to just below 500rpm.


I am reading conflicting advice on the net, with some experts claiming idling an engine is bad. While others say idling for extended period of time is bad, but there is no definition of what entails "extended period of time", though I assume it means well more than start-up idle, so over 15 mins.


So is it good or bad to let my LML idle for a couple of minutes , until the RPM has settled down?
imho, it depends on what you are going to do with the truck.

In cool (not cold) weather I usually wait for it to idle down (mine trucks have all lived outside, and I use remote start, so that doesn't mean I'm sitting in the truck waiting for it)

You should enable the 'elevated idle' function.

When it's warm, it will do nothing.
When it is cold enough (ambient and engine coolant temp) it will run the idle at 1050 rpm. It also sets the torque converter, fan and turbo to create more heat. This also warms the transmission oil.


If your truck lives outside, remote start and the 'elevated idle' are your friends in the winter.


Remote start will run the truck for 10 minutes. It can only be used twice and then a key cycle is required before it can be used again.
(the fob can be used to extend the first cycle -- but the time extension counts as the 2nd cycle)


There is a bunch more info about 'elevated idle' in the duramax supplement.
(Don't confuse this with the 'high idle'; or 'fast idle' function which is for a different purpose, and needs to be activated manually)
Once coolant temp reaches about 150F, the 'elevated idle will shut itself back off.


Elevated idle is supposed to only work below 32F. This was true on my LML, but my L5P seems to engage elevated idle a few degrees above 32F, although I haven't been able to sort out what the limit is.
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post #4 of 68 (permalink) Old 11-14-2019, 02:22 PM
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Mine is a 2006, but the owner's manual says "When your engine is cold, let it run for a few minutes before you move your vehicle. This lets oil pressure build up. Your engine will sound louder when itís cold."
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post #5 of 68 (permalink) Old 11-14-2019, 02:32 PM
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I just discovered fast idle on my L5P last night.

Usually sleeps in the garage, but on a trip yesterday it sat out all day. 35F when I started it and it idled up to about 850 or so for about 10 minutes. Had the truck a year and never seen this before.

the high idle option is not listed on my build sheet and I have not made/changed any settings for this, so assume it is something built into all trucks, like the coil spring choke on a Rochester Quadrajet. (Ahh, the good old days...)

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post #6 of 68 (permalink) Old 11-14-2019, 02:40 PM
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I remote start and let mine idle for 10 mins in the mornings-and plug it in over night. Been in the 20ís lately.

All other times, even in summer, I start and wait at least 30 seconds if itís been sitting. I just feel it allows for fluids to get to the right place.

If your truck is emissions intact then maybe just make sure you have a good long drive sometime through the week.
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post #7 of 68 (permalink) Old 11-14-2019, 03:18 PM
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If it makes you feel any better my trucks been remote started for the last 15 minutes so i can be warm on my way to lunch.
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post #8 of 68 (permalink) Old 11-14-2019, 04:29 PM
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post #9 of 68 (permalink) Old 11-14-2019, 05:41 PM Thread Starter
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Quote:
Originally Posted by redwngr View Post
imho, it depends on what you are going to do with the truck.

In cool (not cold) weather I usually wait for it to idle down (mine trucks have all lived outside, and I use remote start, so that doesn't mean I'm sitting in the truck waiting for it)

You should enable the 'elevated idle' function.

When it's warm, it will do nothing.
When it is cold enough (ambient and engine coolant temp) it will run the idle at 1050 rpm. It also sets the torque converter, fan and turbo to create more heat. This also warms the transmission oil.


If your truck lives outside, remote start and the 'elevated idle' are your friends in the winter.


Remote start will run the truck for 10 minutes. It can only be used twice and then a key cycle is required before it can be used again.
(the fob can be used to extend the first cycle -- but the time extension counts as the 2nd cycle)


There is a bunch more info about 'elevated idle' in the duramax supplement.
(Don't confuse this with the 'high idle'; or 'fast idle' function which is for a different purpose, and needs to be activated manually)
Once coolant temp reaches about 150F, the 'elevated idle will shut itself back off.


Elevated idle is supposed to only work below 32F. This was true on my LML, but my L5P seems to engage elevated idle a few degrees above 32F, although I haven't been able to sort out what the limit is.
I have no idea if my truck has the "elevated idle" option. It does not have remote start, far as I can tell.
Will I be able to use a scanner tool to find out if it has elevated idle?

I am also a but confused on what elevated idle does. Do you mean it runs the engine at 1050 rpm all the time when it is idling, and this RPM never drops? And how does it set the torque converter, fan and turbo to create more heat? Does this higher heat generation subside once the truck has been on the road a few miles, or does it always maintain a specific minimum temp? Does it noticeably affect fuel economy?

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post #10 of 68 (permalink) Old 11-14-2019, 05:59 PM
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Quote:
Originally Posted by J83 View Post
If it makes you feel any better my trucks been remote started for the last 15 minutes so i can be warm on my way to lunch.
Knowing I'm not the one going to lunch at 4pm...it does make me feel better.

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