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T-Stat Question

Old 06-05-2010, 12:24 PM
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I currently have the factory recommended 195 T-Stat and my jeep is running a little over 215, i know that's not a horrible operating temp, but i would like it lower with the high temperatures that are coming. I had a renix cherokee before and it always ran cooler than my '99. Anyways, if i put in a 180 stat would that mess with my ecm in any way? And for those who have ran the 180 what does your jeep run at?
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Old 06-05-2010, 12:41 PM
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i would like to know also cuz im running at round 230
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Old 06-05-2010, 02:00 PM
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No effect on an a OBD-II ECM and with summer time ambient temps, a 180F t-stat will have no effect on max coolant temps. Remember, the t-stat only controls MINIMUM operating temps. Been running a 180F t-stat in our XJ for 6 mos now.......cold/winter ambient temps coolant temp is 180F-190F, hot/summer ambient temps coolant temp peaks at 215F. These numbers are by the ScanGauge.
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Old 06-05-2010, 02:21 PM
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I would suggest you diagnose the problem and fix it. Using a lower temp T-stat won't help and could make things worse. Replace your rad cap, flush the coolant, check the function of your fans, have system pressure tested. You might have a dieing water pump, plugged radiator, failing fan clutch or temp sensor even bad hoses.
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Old 06-05-2010, 02:38 PM
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Does this pic resemble the factory temp gauge/marks?
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Old 06-05-2010, 04:00 PM
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All these things run hot. I blame it on the tiny radiators and tight engine compartments. When my buddy owned it we put in a heavy duty radiator and removed the under hood mat. That helped some. But when I got it I also noticed that it would still get above 210* in traffic, so I wired the electric fan with a switch and relay so that I could turn it on manually whenever I wanted. When in traffic I can switch that fan on and the temps will stay around 210* in traffic. I plan to cut the core support and lower the bottom section so that I can fit a taller radiator in there. Overheating is the biggest problem with 4wheeling since you're always at low speeds. I might also ditch the clutch fan for another electric fan but I have to find a suitable candidate for a junkyard swap. I have Dodge Intrepid fans on my Monte Carlo and they will hold a magazine to the grill on high speed and they cool TONS better than the original clutch fan ever did.
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Old 06-05-2010, 04:41 PM
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Originally Posted by djb383 View Post
Does this pic resemble the factory temp gauge/marks?
Yes sir, that resembles the temp gauge. Thank you for taking the time to post the picture up. I guess mine is running about 230 then. The clutch fan & e fan are working properly, and the coolant has been flushed recently. I haven't noticed any leaking from the water pump so i assume thats working correctly also. I don't really understand what you mean by the t-state only controls minimum temps though...
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Old 06-05-2010, 07:44 PM
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180F thermostat for example.. when it reaches 180degrees, it opens. It stays open as the engine contenually warms. Closes when the engine cools to less then +/-180..

Thermostats allow the engine to reach opporating temperture faster before allowing the coolant to fully circulate. If XJs had perfect cooling systems, a thermostat would in fact regulate the opperating temp to a certain degree...
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Old 06-05-2010, 07:52 PM
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Also, my buddy had a 798 Bronco Big Block with cooling issues, we went to the junk yard and got a couple of electric fans from a cadillac with a Northstar V8.... Those suckers are like Jet Engines.... I'm gonna put a couple in my XJ next month.
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Old 06-05-2010, 09:21 PM
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Originally Posted by The91XJ View Post
.........I don't really understand what you mean by the t-state only controls minimum temps though......
When the t-stat begins to open, coolant begins to flow to the rad where heat is removed. Whatever the t-stat's opening temp is, that will be the minimum coolant temp because that's when coolant will begin to flow and is also when it begins to cool. Ambient temp, air flow and rad surface area are the main factors in determining max coolant temp. In cool/cold weather, the t-stat seldom opens and very little when it does open. Hot weather, t-stat is pretty much wide open all the time, after initial engine warm-up.

84supersport hit the nail on the head with his statement about a tiny radiator in the XJ. A rad that's less than a foot tall, pahleeeese. Rad surface area is more important than the number of rows but you do have to live within the space allotted. The rad on our Toyota Corolla has way more surface area than the XJ. Hottest the ScanGauge has ever displayed on the 'rolla is 196F. Ambient was 111F here in the desert today.

Last edited by djb383; 06-05-2010 at 09:24 PM.
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