Engine temperature gauge fluctuates

John Middleton

TJ Enthusiast
Supporting Member
Joined
Dec 13, 2017
Messages
145
Location
Missouri, United States
2 1/2 hrs into 3 hr drive in my 03 Rubi; temp gauge goes into red zone & light comes on. Pull over, check AF-OK, serpentine & water pump; no issues. Start engine after 2 minutes; back in normal zone. Finish drive. 3 hr drive home & watching temp gauge: occasional brief creep into red zone with two issues of warning light coming on. Gauge goes back to normal.
Any thoughts? I'm thinking sticking Tstat?? Or new radiator.

Also noticed transmission temp (I have a gauge reading pan temp) is also fluctuating between 180 & 200which is new. Related?
 
When was the last time you flushed your system and replaced the coolant?

Because it only takes a few minutes to return to the normal zone, my money is on a sticky t stat. Start there. It's only $20 for the Mopar part. While you have everything torn down, might not be a bad idea to also replace the water pump.
 
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Agree with the thermostat.

You may already know this, but if your engine overheats and you need to keep driving, roll down the windows and blast the heat at it’s hottest setting and highest fan speed. That will help slow down (but not stop) the overheating. Still pull over as necessary to let it cool down.
 
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I have a question on the thermostat diagnosis that hopefully you guys can answer. If it started to overheat 2 1/2 hrs into the trip, I'm assuming the engine would have been at normal operating temp prior to that point and the thermostat would have been full open. I thought if it was sticking and not full open it have reared its ugly head sooner and shown some symptoms or would have been running hotter than normal the whole trip? I wouldn't think the thermostat would cycle open/ close and potentially stick late in the trip unless he stopped at the 2 1/2 mark for a bit.
 
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A bad thermostat can cause some funny issues. If it is binding up it could open in some warm-ups but not others. It is definitely suspect.

Other possibilities could include clogs in the radiator tubes, inadequate airflow, or even water pump issues. Do you have stuff blocking the grille like a winch, lights, grille inserts, grumpers, etc.?

When you flushed it, did you use a chemical to dissolve deposits?

What engine RPMs are you running at? (High load at low RPMs is more likely to overheat than at higher RPMs.)
 
There is a winch (Warn 8274 & cover) but never been an issue before.


A bad thermostat can cause some funny issues. If it is binding up it could open in some warm-ups but not others. It is definitely suspect.

Other possibilities could include clogs in the radiator tubes, inadequate airflow, or even water pump issues. Do you have stuff blocking the grille like a winch, lights, grille inserts, grumpers, etc.?

When you flushed it, did you use a chemical to dissolve deposits?

What engine RPMs are you running at? (High load at low RPMs is more likely to overheat than at higher RPMs.)
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It's cheap and easy so I'd start there too. I was under the same impression as what Steel City said that a sticking Tstat might open on some starts but not others so I was questioning if sticking thermostats can show up as other symptoms.
 
So, for all you Stant stray guys, ordered one online & put it in. OEM tstat had “top labeled on it & I put the new tstat in with same orientation.
BUT, the Stant dome was slightly thicker and presented a clearance issue which wasn’t apparent until a nice stream of antifreeze began dribbling from the cracked housing after install! Cheap oreily one would have worked fine. New housing on order & Jeep down for another week!
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Stant tstat must be oriented at ten & four to clear housing.
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I seriously doubt the Stant thermostat you installed had anything to do with the leak. It's by far the most popular thermostat recommended here and I've installed 4-5 myself without ever having a leak. You just have to make sure it doesn't slip down out of place as you place the thermostat housing over it.

Too many of us use Stants on our TJs without problem or leaks.
 
I tend to agree with Jerry. Wonder if the housing was dropped in the past compromising the integrity. Hard to believe torquing that bolt could crack a perfectly good housing.
 
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Jerry, i take issue in your doubting my mechanical ability. My post was to inform that there was a clearance problem with the thermostat & housing if installed at 12 o'clock position. It was evident when I pulled the housing off and rotated thermostat in housing on bench. No, it didn't slip down on installation and this ain't my first rodeo! New Leprechan housing, stant tstat & felpro gasket--Jeep rides again.