Cooant Temp Fluctuation

[WPlucker]

Just traded in my 08 Mega Cab, on a 2012 Laramie 4X4 Crew Long Bed. My question is on the coolant temp readout on the dash. I can watch the temp range from 195 to 205. It fluctuates constantly while driving. I haven't checked it at idle to see if it stabilizes. Just wondering if anyone else has this happening. Haven't taken it to the dealer yet, but am curious on peoples responses.

 

[Bob4x4]

It has a 200 degree t/stat,Cummins t/stats aren't known for there steady temps. A replacement may have smaller swings. If you are running empty it will be more noticeable due to the huge radiator and small heat load.

 

[DAWG-1]

My 2011 does the same thing. Mine runs between 199* to 208*. I was concerned at first but it is consistant. So no worries. Sam.

 

[WPlucker]

Ok, just have never seen that happen in any vehicle that I have worked on. I am a diesel mechanic, and have worked on everything from John Deere to ISX Cummins, and C-15 Cats. Usually the problem lies in the sensor, and not the t-stat. It should hold a constant temp once warmed up.

 

[ata]

Temp swings are normal for Dodge Cummin's running empty.

 

[rscurtis]

It was an issue in early 2nd generation trucks IIRC.

 

[mwilson]

Ok, just have never seen that happen in any vehicle that I have worked on. I am a diesel mechanic, and have worked on everything from John Deere to ISX Cummins, and C-15 Cats. Usually the problem lies in the sensor, and not the t-stat. It should hold a constant temp once warmed up.

A result of the way, way oversized cooling system.



Thermostat opens and a flood of coolant at a lower temp from the radiator hits the block, drops the engine temp immediately and the thermostat closes.



If you are running the truck loaded and working the crap out of it you will not see the fluctuations that you do running along empty.



It is normal with these trucks.



Mike.

 

[Oil Stain]

Hi I'm new here, great site! Money well spent for a change!

Mine just statrted to do this as well. I'm always the gauge on my Mini Max. Coming up on 6k miles and never saw that big of a swing. Always saw 199-201 if anything. Now seeing 197-204. It looks like the t-stat is opening and closing really fast. If it did it from day one, I wouldn't be concerned, but it just started. Yes this is running empty. Haven't tried towing yet, I'm a little nervous. I use to drive Chevy astro vans and this would happen when it's really cold outside, but this was at 70* at night.

 

[AH64ID]

It's normal.

The thermostat cracks at 200°, but isn't full open until around 217°-219° so there is lots of room to swing with the oversized cooling system. As the thermostats age it does get a little worse, when I changed my thermostat at 50K miles my swings slowed down. Since it takes a good load and a good grade to get the thermostat to go full open they develop a wear pattern and weaker spring that doesn't regulate as finely as when new.

 

[Oil Stain]

It's normal.

The thermostat cracks at 200°, but isn't full open until around 217°-219° so there is lots of room to swing with the oversized cooling system. As the thermostats age it does get a little worse, when I changed my thermostat at 50K miles my swings slowed down. Since it takes a good load and a good grade to get the thermostat to go full open they develop a wear pattern and weaker spring that doesn't regulate as finely as when new.

Thanks for the quick reply, I knew it had to be the stat but after 6k miles it had me worried with the programmer and stuff. I take it easy and I paniced thinking it could be the start of a headgasket but, I know the temps would go thru the roof.

 

[RustyJC]

The thermostat cracks at 200°, but isn't full open until around 217°-219° .....

In case anyone's interested, cooling fan full engagement seems to take place at 221° according to the EVIC digital readout on my truck. This was discovered towing our 16,000 lb GVWR 5th wheel up some long West Texas grades on a 100°+ day this past September. Once engaged, the coolant temperature drops pretty quickly.



Rusty

 

[jkern]

Something that I have noticed as well. I do have a question: If ones truck is deleted (DPF and EGR for obvious off road purposes only), Should the thermostat be replaced with one of a lower temp? I think the main reason to run these truck so hot is for emmisions purposes. my 99 had a 180* (i think). I would think that a 170-180 degree thermostat would provide a little longer life and cooler temps towing on hot days. 221* coolant even before the fan is completely engaged is awful hot for a water cooled engine.

 

[AH64ID]

I personally would stick with the OEM temp. There is lots of discussion on this, and if you run empty all the time it's probably not a big deal but if you tow stick with OEM. The reason is the fan programming vs thermostat temp. The fan is programmed around a 200º thermostat, when you put at 180º thermostat in you loose the fan operation at the proper temps. A 180º thermostat cracks at 180º, goes full open at 198º, with a max allowed (per Cummins) temp of 212º. So at 221º you are well above the max temp for the thermostat, and that means your not transferring heat properly.

In addition without the fan programmed for the thermostat temp you will get larger and wilder temp swings, and that is harder on parts than a constant, but higher, temp.

 

[goodguys75]

Something that I have noticed as well. I do have a question: If ones truck is deleted (DPF and EGR for obvious off road purposes only), Should the thermostat be replaced with one of a lower temp? I think the main reason to run these truck so hot is for emmisions purposes. my 99 had a 180* (i think). I would think that a 170-180 degree thermostat would provide a little longer life and cooler temps towing on hot days. 221* coolant even before the fan is completely engaged is awful hot for a water cooled engine.

the truck is designed to run at a certain temp, if you lower it it will start to mess with the electronics and emissions... its not like older vehicles that benefit from lower coolant temps... to many sensors and emissions makes it that way... . if i could i would run it below 180 deg. here in Vegas during the summer

 

[EDankievitch]

Think about how big that Rad out front is it cools off when the stat is closed. The block warms up the stat opens and all that cool coolant comes rushing in. Swings from 195 to 208 are normal.....

 

[MChrist]

I noticed the temp. swing on my 2012 5500 as well. What really surprised me, however, is the speed at which it swings. From 195 to 213 may only take 10 seconds, and less time to drop back down.

 

[Roostre]

Diesels are more efficient at higher temps. The VW diesel guys have a thread where they modified thermostats and tracked fuel economy... around 200°F turned out to be the sweet spot on those. (my wife drives one) When her thermostat went bad she lost a full 5 mpg.
The powder stroke guys can get a 203° stat that improves their mileage a bit also.

 

[Teich]

Coolant temp stayed steady until i change the water pump and stat then it started replaced the rad no better noticed that rad wasn't right full after running overflow tank was full then really full still didnt help, the fix was a clamp on the overflow hose at the rad end now 100% Laurie