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Old 12-14-2019, 03:03 AM
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Jeep over heats in summer and doesn’t heat up in winter

I have a 94 yj 4 cyl I am having trouble finding the cause of this but if I run my Jeep a little too long in the summer it over heats like it will boil the coolant like my thermostat is stuck closed then in the winter I’ll go start it in the morning for like 20-30 min and when I get out there it’s not warm at all maybe just over 100 on the temp gauge but as soon as I start driving it slowly heats up to 210 witch is normal but if I stop somewhere and let it idle for 5 min it drops down to 120ish kinda like my thermostat is stuck open and my heater used to make me sweat and now it’s just kinda warm so here is what I have done
and still does it

Thermostat 190
Drained radiator
Flushed it both ways with a hose
Flushed heater core
Flushed with blue devil ratiator flush
Refilled with concentrate and water 50/50
Blew my heater core out with compressed air
And tied my vent door shut

It doesn’t burn coolant or leak it at all but I’m not understanding why is would go from not heating up in the winter to boiling the coolant In the summer
Any ideas?

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Old 12-14-2019, 03:09 AM   #2
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My guess is that your new stat is crappy, get a 195* stant superstat, and that your water pump may have seen better days....

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Old 12-14-2019, 03:12 AM
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Quote:
Originally Posted by Gottagofast View Post
My guess is that your new stat is crappy, get a 195* stant superstat, and that your water pump may have seen better days....
Okay I’ll try that it’s a bit cold here might have to wait on the water pump tho
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Old 12-14-2019, 03:18 AM
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I should also mention that I changed my clutch fan as well to keep from over heating this summer helped a little but still got hot in the summer it kinda cools down when I go down hill and in the winter it cools down a lot
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Old 12-14-2019, 05:54 AM   #5
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Test the thermostat to make sure it is fully opening, or not stuck in a partially open position. If you need a thermostat I would buy an OE thermostat. It could also be the water pump, radiator, etc. But I'm thinking the thermostat is bad.
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Old 12-14-2019, 07:22 PM   #6
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Do sound like a bad thermostat or poor quality one. Ive had pretty good luck with Murray Tstats from Orieleys. I dont know why but in my decades of driving Ive had several thermos go bad from short trips which never allow full opening or closing. Our work truck F250's were pretty bad for that one, they'd just get hung up open part way and stay like that. That or extreme cycling of the temp. Going from closed heating up to 230 or so then a rush of coolant dropping the gauge to 120ish and repeating this for miles on end. This happened during colder weather mostly. Hate to say it but Napa thermos have been some of the most problematic.
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Old 12-14-2019, 09:05 PM   #7
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Dollars to donuts it's the water pump.

Do the water pump, install a 195* MOPAR thermostat and be done with it.

Good Luck, L.M.
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