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Discussion Starter #1
I have an 06 LLY 2500 with the 6-speed Allison that has developed a fluctuating engine coolant temp condition in the last 2500 miles. The truck is bone stock. I've noticed that the temp gauge now fluctuates from 180 to 200 while driving. Up to this point, (truck has 25,000 miles on it) the temp gauge has stayed rock solid at about 195.

Truck is used for daily use and to haul a 20' cattle trailer occasionally.

Had both thermostats changed at the dealership and it is still doing it.

Anyone have any suggestions?

I found one other post on this dating back to Jan of 06, but there was not much help offered.

Should I be concerned?
 

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Philntx;1584504; said:
I have an 06 LLY 2500 with the 6-speed Allison that has developed a fluctuating engine coolant temp condition in the last 2500 miles. The truck is bone stock. I've noticed that the temp gauge now fluctuates from 180 to 200 while driving. Up to this point, (truck has 25,000 miles on it) the temp gauge has stayed rock solid at about 195.

Truck is used for daily use and to haul a 20' cattle trailer occasionally.

Had both thermostats changed at the dealership and it is still doing it.

Anyone have any suggestions?

I found one other post on this dating back to Jan of 06, but there was not much help offered.

Should I be concerned?
Mine is a 2007 classic with the LBZ with only 3K miles on it and it does the same thing when the weather is very cold. Otherwise when the temp is about 30 or higher it stays right at 195.
 

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I have also noticed this, I thought it was becasue of the ULSD that I started using.
 

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Sounds like normal t-stat operation. Engine get's up to 200 then the t-stat opens (with the cold weather the rad has real cool water) new coolent comes from the rad (colder) and enters the engine causing the tmep gauge to lower. My truck does the same.
 

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Normal. As stated, thermostat opening.
 

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06bowtie_guy;1584875; said:
Sounds like normal t-stat operation. Engine get's up to 200 then the t-stat opens (with the cold weather the rad has real cool water) new coolent comes from the rad (colder) and enters the engine causing the tmep gauge to lower. My truck does the same.
:exactly:
 

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I have the same thing since winter temps set in. Used to ride bone steady on the 195º peg, but now will vary from 160-195º. The colder the temp the quicker the drop from 195º to 160. Then it slowly builds back up and drops. Amazing how that cold coolant rapidly cools the engine temp once the thermostat opens. I've been running my grille cover now that the temps stayed consistently below 20º. That seems to have helped the temp recover once is drops to 160.
 

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Noticed the same thing happening on mine too.
 

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What's the outside temp running in your area?
Anything below 70*F and mine does the same thing. Big radiator and cooler temps= swings on the gauge like you're seeing. Normal.
 

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Discussion Starter #10
Temps have been in the 40's and a couple of weeks in the 30's.

Didn't do it last winter with the same temps.
 

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My 07 fluctuates quite a bit. Its obvious when the thermostat opens as it drops dramatically. Temps up here have been in the low single digits and below zero. My grill cover has been on for about a month now and it runs at around 180-185 steady highway cruise. Diesels just dont generate enough heat to keep them warm unless you're working it. I can stop, throw it in park with temps in the low single digits or below zero and the high idle will kick on in about 15 minutes. What you're seeing sounds 100% normal.
 

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I agree with the posts saying the t-stat is working and causing the swings.

I did starte using the upper half of the winter front and that helped stady the guage. As well as reducing time to temp in the cold. Its been in the teens with some nights as low as +2F around here for the last two weeks.

I run the winter front below 30F.
 

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At least the gauge moves. The Ford's are an idiot light with a needle. It stays in the same place from 170-230. Mine moves like the original post in cold weather...so did all the Cummins trucks I have owned.
 

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Have noticed mine doing the same thing since it has got cold. Didn't notice it during the fall or early winter. Have had winter cover on for almost a month. That's when I started to notice it.
 

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once it got below 40 i put my grille cover and never looked back, ive got good heat and coolent gauge goes up to 190-195 and stays there
 
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