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Discussion Starter · #1 ·
My 89 Trooper w/ 2.6 seems to be running hot recently. On my 15-20 min drive to work while driving at highway speeds it gets just past 3/4 on the gauge. When I pull off the highway and start driving slower it tends to decrease back to the middle. It hasn't got to the red on the gauge and I haven't done a much longer drive to see if it would continue to climb towards red.

I took it to my mechanic and he said he couldn't find anything wrong and that everything was fine but it's happened a few times since. Mentioned the radiator wasn't clogged.

Here are some things I checked. Coolant is topped off and doesn't seem to be leaking. I did my best to burp the system not too long ago. No obvious signs of head gasket issues. I replaced the water pump, temp sending unit, and coolant temp sensor when I rebuilt the motor last summer.

Not sure if this is related but I do notice sometimes after I step on the clutch and/or idle, the revs will bounce up and down between 1100 and 1600 for a little while before they settle. I read that this could be air in the system passing by the Coolant Temp Sensor. Also, right before this started happening, I used the heat for the first time since last year, but I know that normally helps cool the engine.

I've read through a lot of posts on overheating but thought I'd ask for thoughts on my issue. I was planning to take the car a couple hours from my house to the George Washington National Forest this weekend but I'm having second thoughts since this started happening.

Any ideas on what might cause this and what I can troubleshoot? I assume driving on 3/4 on the temp gauge probably isn't a good idea.

I'm going to try to burp it this afternoon since that's pretty easy to do.

Thanks!

Mike
 

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I recently went through something similar. Fresh rebuild ran 50% on the temp gauge and would hit that mark two minutes into a drive... Thought it may have been an aftermarket temp sensor .. it ran terrific etc and the heater was damn hot!
Long story short it popped the head gasket b/t 2&3 at 5k miles on a fresh top and bottom build and when i took it down the small water passages were clogged with some stopleak that was left over in the system somewhere from previous owner. I bought it with a bad crank and rebuilt.
Built another head as that one was warped and drilled the other row of unused coolant passages on the new head gasket and now it sits right about 1/4 to 1/3 on the temp gauge and never goes above. I didn't have any signs of head gasket leaking into the coolant before it went nor after... would still run on two cylinders and got me home without blowing coolant too.
Just my two cents but those passages are small and easily clogged.
Mike
 

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Step 1, Check for cold spots on the radiator
step 2, check for proper coolant flow
step3, Check cap for proper seal
step 4, check for air bubbles in cooling system.
step 5, check for failed head gasket.

if you find no issues you must have a inaccurate temp gauge.
 

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My 89 Trooper w/ 2.6 seems to be running hot recently. On my 15-20 min drive to work while driving at highway speeds it gets just past 3/4 on the gauge. When I pull off the highway and start driving slower it tends to decrease back to the middle. It hasn't got to the red on the gauge and I haven't done a much longer drive to see if it would continue to climb towards red.

That above mentioned event seems backwards. At highway speeds you should have much more cooling air going through the radiator than at speeds slower than on the highway. Do you have a fan shroud? And is your fan positioned at about the halfway point into the shroud. Tests on cooling systems have shown this to be the best position for max air flow. Do you have the larger plastic fan? Is your fan clutch working.
 

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Discussion Starter · #5 ·
Thanks for all the feedback. I’ll start checking these things.

I saw Johnny posted a video on drilling the holes for the row of unused coolant passages on replacement head gaskets after I rebuilt my engine. Wish I had known that before if that seems like a good thing to do.

It does seem odd that it would run hot at high speeds and cool down at lower speeds. I have a fan shroud and the plastic fan seems to fit centered pretty snugly in there. I’ll have to test the fan clutch as I work through this.
 

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I find a infrared thermometer really helpful. My temp gauge has always been just under the middle (12 o'clock). In triple digits and climbing a hill it would barely go just a hair over the middle.
The other day, driving home from a lake, it went 3/4 of the way up and I thought my 89 is overheating, checked all the temps with the infrared and it was perfectly fine. Turned out, my temp sensor went bad. Now that I have a new sending unit, it never goes over 1/4 which is also annoying because that probably means if it goes to the middle it will be too hot. Unwilling to put up with this uncertainty, I installed a aftermarket temp gauge that actually tells me where I am at.
Also, the fan clutch can go bad, keep us posted please!
 

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Discussion Starter · #7 ·
My mechanic looked at it and thought it was the radiator. I ordered one from RockAuto and will be installing it later this week along with a new thermostat for good measure. I think it might be the original radiator, or at least quite old, so I don't mind replacing it with a new two-row one while troubleshooting. I recall when I replaced the heater core due to a leak, the core I pulled out had a bunch of stop leak on the outside. Maybe that stuff someone poured in is also clogging up the radiator.

Mike
 

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Discussion Starter · #8 ·
I cleaned the system then replaced the radiator and thermostat this past weekend. The old radiator looked rough but apparently had been replaced in 2017 and was the same as the model I put in. The old thermostat fell apart in my hand once I pulled it out. I drove it to work today and it drove well but the temp still sat a couple notches past center on the gauge. It didn't seem to go any higher or get as high as before. Still kind of worries me though but maybe I'm paranoid.

Before I replaced that stuff, in order to try to eliminate headgasket issues as a potential cause, I checked compression and got what I thought were good results. All cylinders got a reading between 155 and 165.

I ordered a new sending unit when I ordered the rest of the stuff. Should I swap that out?

I did the water pump (and sending unit) last summer when I rebuilt the engine so I'm hoping that isn't an issue.

Thanks,

Mike
 

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+1 for ir thermometer... ebay amazon harbor freight under $20 ... get a real number for the temp any spot you point it.
If i remember ill shoot the head tomorrow on my 4ze1 with a 180 thermostat.
 
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