Cold temps cause a diesel to have a more lopey idl

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I've always noticed on my truck that when it's cold out and you let it idle for more than 5 minutes or so that the idle gets a little bit choppier. This is when the engine is warm. The truck still runs smooth and everything.
 
We did a post on Jan 8, 2018. It was entitled “Oil for cold starting diesels”. It talked about more than just oil, but what viscosity oil are you running and is it conventional or synthetic? If it’s the 15-40 you have at the bottom of the page, that’s part of the problem.

SF
 
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15w40 but I'm talking about even once it's warmed up it has more of a lope compared to the outside temps being in the 90s
 
Originally Posted By: Snagglefoot
We did a post on Jan 8, 2018. It was entitled “Oil for cold starting diesels”. It talked about more than just oil, but what viscosity oil are you running and is it conventional or synthetic? If it’s the 15-40 you have at the bottom of the page, that’s part of the problem.

SF


15w40 is not an issue in Houston, Texas.
 
Some might argue all diesels do this in the cold but I have one piece of advice. I checked the owners manual the 2007 Dodge Cummins 6.7 . Your owners manual says at cold temps you can use 5W-40 motor oil and that it’s OK to use synthetic oil. I would like to suggest 5W-40 synthetic oil for diesels. Delo probably has it.

SF
 
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Originally Posted By: motor_oil_madman
15w40 but I'm talking about even once it's warmed up it has more of a lope compared to the outside temps being in the 90s


Your diesel fuel is still cold. Probably not atomizing as well or if you check out that posting I described, some guys had advice on mechanical items.

SF
 
Diesel fuel doesn't like cold temperatures and it's various properties are temperature-dependant. Since the fuel is coming from storage, whatever ambient temperature your fuel tank is at will affect it's combustion properties; not engine operating temperatures. Truckers and heavy equipment operators use diesel fuel conditioners to make diesel happier with cold temperatures.
 
Makes sense. That a long with the combustion temps getting low again after 5 or 6 minutes probably doesn't help either.
 
Originally Posted By: Snagglefoot


SF


15w40 is not an issue in Houston, Texas.[/quote]

36 F tonight in Houston. Just sayin.

SF

[/quote]


It normally isn't this cold. We were sitting at 25-30 degrees for like 3 days straight. Usually it only does that for a night or two this time of year and even that only happens every 2 or 3 years. So I don't experience this choppy idle issue that often. The other day it got down to 19 over night and when I went to drive the truck in the morning it made the loudest noise when I put it in reverse. Parts of the drivetrain were frozen together. Lol I think it was mainly the tires though.
 
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It's comical to listen to a guy from the south talk about what he thinks is cold it always make my day.
 
Originally Posted By: motor_oil_madman
Makes sense. That a long with the combustion temps getting low again after 5 or 6 minutes probably doesn't help either.
Your Ram has the same feature mine does-when it's not fully warmed up & allowed to idle more than a minute or two it raises the idle RPM to 1000 and starts firing on every other cylinder, which allows the engine to warm up without "wet stacking" and contaminating the oil with excess fuel.
 
The common rails don't do the every other cylinder thing. It will raise to 1000 rpm but it's still firing on all cylinders. If it's real cold it will go straight to 1000rpm as soon as it starts.
 
Originally Posted By: dave123
It's comical to listen to a guy from the south talk about what he thinks is cold it always make my day.


Amen! It made it back up to 40 yesterday and it felt like a heat wave. Driving with the window partially open..
smile.gif
I was thinking about how easy the truck had it, and my auto start stop even engaged since it had warmed up enough
smile.gif
 
CT8 said:
That is because it is cold.Compression ignition ya know. [/quot


So even after it's all nice and warmed up it will still have more of a lope once it idle for 10 minutes or so and the egts drop?
 
Your engine has a very powerful Air Intake Heater Grid, Cold air is not an issue as the ECM will pulse the heater grid if IAT's drop below a certain threshold, (Mid 50's & below IIRC)
Your truck also has a fuel heater that is thermostatically controlled (Keeps the fuel temps about 18 degrees above freezing)

As you can see, Modern diesels have features to keep them running smoothly in freezing temperatures if the engine is in good repair.

I recommend having your Injector Balance Rates checked with a capable scan tool, Anything under/over 4-mm3 for any cylinder means the ECM is Adding or Subtracting too much fuel for a healthy Injector/Cylinder.

IF you want a more conclusive test after checking balance rates......Have a INJECTOR RETURN FLOW TEST performed on each Injector.
 
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