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comanche overheating at highway speeds


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  • 3 weeks later...

New rad fixed my overheating problems..picked it up from autozone..spectra I think Chinese made I suppose ...as much as I would love to put in that aluminum radiator can't afford it atm.. Autozone has lifetime warranty on them so I'll take a chance.. Thanks for the help guys

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  • 1 year later...

I've been overheating the last couple days as well. Checked my Haynes Manual for trouble shooting, but it says that Comanches/Cherokees have a closed system with the reservoir cap acting as a pressure cap as well. My truck definitely does not have that system. In fact, it has two, possibly even four small holes in the reservoir tank that fluid leaks out of now when the engine is turned off and coolant flows back into the tank. Engine fan is running, coolant is filled to "fill" line. A very recent problem, just started the last few days. Any ideas?

 

It almost looks as if holes were drilled into it? Maybe there was a label or something on there originally that fell off or something? Are there supposed to be holes? Doesn't look right to me...

 

IMG_5735.JPG.5dac984efc965084b0085493a6e47c91.JPG

 

 

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On 6/23/2018 at 2:24 PM, HOrnbrod said:

No, there are no holes in the 91-92 MJ expansion tank - you need to replace it. 91 and 92 had an open cooling system. Your problem sounds like a faulty radiator cap - replace that too.

 

Yeah I don't how the hell those holes got there! Anyway, replaced that, Napa had the part for $25 easy fix... Pushed it hard on the trails yesterday and it's only reaching near the red zone (about 250 degrees) under the most extreme climbs. Had to kick the heat on again from time to time. New res tank seemed to help some but not completely. The radiator cap is sealed tight so that's not the issue. All the hoses look okay so that's good news too. What I think it is actually is the engine fan clutch is bad. Correct me if I'm wrong, but when the engine gets to normal operating temp and you shut the engine off, you shouldn't be able to spin the fan freely at that point with one finger. There should be some tension there right? Anyway, going to replace that and see what happens. A full system flush probably wouldn't be a bad idea either.

 

Also, was reading this today and it says the off-road package (which I'm pretty sure I have due to the skid plates, Dana 44 rear, etc.)  also included a bigger radiator. Can anyone verify this? 

 

"The optional 4x4 Off-Road Package included high-pressure gas shocks, front tow hooks, a heavy-duty radiator, and front skidplates. There was also an available Trac-Lok rear diff for the 4.0L (if the truck had the fullsize spare)." 

 

http://www.fourwheeler.com/project-vehicles/154-0610-jeep-comanche-mj/

 

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5 minutes ago, Pancho975 said:

The radiator cap is sealed tight so that's not the issue.

 

That cap's seal doesn't mean anything. On an open cooling system the pressure is released by the cap into the expansion tank periodically at a certain psi determined by the cap pressure rating. Over time the cap spring gets weaker, and the pressure gets released sooner. As I recall, the stock cap for our HO MJs is 13 pounds, but check to make sure. Replace it with a new 13# cap with a fresh spring, or one rated slightly higher at 14#. The higher pressure will allow the system to tolerate slightly more heat before opening, theoretically keeping the system a bit cooler. Try a new cap - cheaper than a new radiator.

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What metal tabs?

There are tabs that prevent the cap from unscrewing itself. But like a child-proof lid on a bottle of Buckleys (or whatever cough syrup you prefer), push down and turn counterclockwise. Once you get the tabs past their holder it'll turn about a half-turn or so, then stop, and it should just pull off. 

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Yeah, you can't just unscrew it all the way. It'll hit a stop, and then you push it down to unscrew it the rest of the way. I guess it's to keep you from accidentally completely unscrewing it if the engine is hot?

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