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Old 07-10-2019, 04:18 PM
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hot engine

2003 4.0 tj driving today with ac on temp about 220 on gauge outside temp 97. Went inside store and came back about 15 min later temp gauge red lined then check gauges light came on. Took about 30 sec and gauge read about 220 again. I have had this jeep for many years and this is the first time this happened

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Old 07-10-2019, 04:21 PM   #2
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Was it running/idling for the 15 minutes you were in the store?

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Old 07-10-2019, 04:28 PM   #3
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Check coolant level, that's a classic symptom of low coolant.

Also, does it still have the fan shroud in place?

Is the fan clutch firm and greasy feeling?
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Old 07-10-2019, 04:58 PM   #4
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Your rig is old and likely in need of a full cooling system overhaul. When was the last time you replaced the radiator, water pump, thermostat and radiator.
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Old 07-10-2019, 05:27 PM
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Jeep was not running when I went into store. Last winter I put on a rebuilt head , cam, lifters, water pump, thermostat, timing chain and gears, the radiator was replaced 4 years ago. Engine has 140,000 miles. I did all of this because a lifter was knocking.. Was thinking about replacing thermostat with a 180.
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Old 07-10-2019, 05:51 PM   #6
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A 180 degree thermostat will not help anything..

What brand did you install last time?

You should only be using a Mopar or Stant superstat 195F non failsafe thermostat. Cheap parts store thermostats are known to fail and stick shut.

Also what brand radiator did you use? Many aftermarket do not cool as well as the factory Mopar rad.
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Old 07-10-2019, 06:01 PM
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not sure about thermostat. I think maybe carquest. All the other parts were mopar
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Old 07-10-2019, 06:02 PM
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The radiator is not mopar but has worked fine for the last 4 years
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Old 07-10-2019, 06:07 PM   #9
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Assuming the coolant level is correct and it is cycling in and out of the overflow tank correctly, sounds like the thermostat stuck...
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Old 07-10-2019, 06:10 PM
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ok thanks ill try a new one
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Old 07-11-2019, 03:56 PM
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Removed the old thermostat today and tested it. Appeared to work fine. Working on putting in a new one on will let you know if that worked.
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Old 07-12-2019, 12:18 PM
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After changing Thermostat with a 180 its still runs at 210 not sure why. From what I can tell today runs fine with A/C off 210 but if turned on runs a little hotter about 225. I did put a pound of Freon in a few days ago. I am now thinking it may have too much Freon which would cause a additional drag on motor. I guess I could let some out. anyone Know the max psi ?
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Old 07-12-2019, 02:57 PM   #13
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As I mentioned above, the correct one to use is a 195F from Stant or Mopar....
180 thermostat will not make the engine run cooler. That is the job of the radiator and fan.
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Old 07-12-2019, 05:19 PM
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What is the point of 195 thermostat vs 180 in texas
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Old 07-12-2019, 05:50 PM   #15
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Nothing in the OP sounds all that concerning. 220, in that kind of heat and with the A/C running, sounds pretty normal.

When you turn the Jeep off the engine is still putting out a lot of heat, but you're no longer circulating coolant or pulling air through the radiator. Coolant temps will always spike when you turn the engine off. 15 minutes is right in the windows where coolant temps will spike highest before. Hot ambient temps plus engine running a bit warm, does't seem unreasonable temps will keep climbing to trip the check gauges light.
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Old 07-12-2019, 10:35 PM
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Thanks. is there a better radiator that is recomended
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Old 07-15-2019, 06:19 PM
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I'm going to try royal purple ice. Heat index 105 today. If this doesn't help I see a bigger radiator in the future
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Old 07-16-2019, 09:14 AM   #18
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Nothing in the OP sounds all that concerning. 220, in that kind of heat and with the A/C running, sounds pretty normal.

When you turn the Jeep off the engine is still putting out a lot of heat, but you're no longer circulating coolant or pulling air through the radiator. Coolant temps will always spike when you turn the engine off. 15 minutes is right in the windows where coolant temps will spike highest before. Hot ambient temps plus engine running a bit warm, does't seem unreasonable temps will keep climbing to trip the check gauges light.
^ to the OP, you're trying to fix what ain't broke. Put the 195 back in.
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Old 07-16-2019, 10:14 AM   #19
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Run a mopar radiator, G05 Coolant, and a 195 thermostat.



Sounds like you have subpar cooling system. I would completely flush whatever coolant you are running and put in G05, and a 195 tstat. Inspect radiator for rust too. Dont mix and match coolant as that can create a nice sludge in some cases. Someone asked and you never answered--hows the fan clutch and is the shroud in place?


Also as already stated--putting in a 180 thermostat does not make your engine run cooler.
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Old 07-18-2019, 06:18 PM
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All the coolant was replaced with GO5 last winter. The problem is that it is so hot this summer it's getting hotter than normal. That is to say it's not in the red but its running about 225 or 230. We all know that 195 is normal. I'm just trying to get it back down. Two bottles of royal purple ice got it down to about 215 to 220. I'm going to let it ride for about a week and see how it works. If it doesn't work I'm looking at getting a bigger radiator
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Old 07-18-2019, 06:24 PM
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The water pump and fan clutch are new mopar. The shroud is in place. The radiator is about 3 or 4 years old. Everything was flushed out last winter when head ,lifters and cam was replaced with all stock mopar parts. It was 99 degrees today with a heat index of 108. It's just to hot....
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Old 07-19-2019, 12:25 AM   #22
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Originally Posted by jeepsk View Post
All the coolant was replaced with GO5 last winter. The problem is that it is so hot this summer it's getting hotter than normal. That is to say it's not in the red but its running about 225 or 230. We all know that 195 is normal. I'm just trying to get it back down. Two bottles of royal purple ice got it down to about 215 to 220. I'm going to let it ride for about a week and see how it works. If it doesn't work I'm looking at getting a bigger radiator
The correct operating temperature is 210F on these engines.
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Old 07-19-2019, 07:34 AM
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Yes thanks 210 that's why its straight up on the gauge. But now that you know everything what do you suggest ?
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Old 07-19-2019, 12:41 PM   #24
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After changing Thermostat with a 180 its still runs at 210 not sure why.
The thermostat determines the minimum temperature. It's like the thermostat in your house in the winter. When the coolant gets too cool, the thermostat routes the coolant back to the engine instead of the radiator to let it heat back up.

The maximum temperature is determined by the temperature difference required between the coolant and the air to exchange the amount of heat the engine is generating. Higher engine load means more heat to reject and the temperature difference has to grow. Higher ambient and the coolant has to be hotter to achieve the needed temperature difference.

If you're running hot that means your radiator is requiring more temperature difference than it should to reject the heat produced by the engine. Reduced air or coolant flow, internal or external fouling (contamination), or poor radiator design can all reduce the effectiveness of the radiator and cause it to need more temp diff to transfer the heat.
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Old 07-19-2019, 12:50 PM   #25
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The radiator is not mopar but has worked fine for the last 4 years
mine worked for a few years too. The problem with aftermarket radiators is they are designed to transfer enough heat when brand new to handle a stock vehicle in perfect conditions and aren't up to task when used in environments typical for a Jeep.

I drive in 100° weather all the time, and at elevation where the air density is 85% or less of that at sea level. Never got hot until I installed a winch which impacted the airflow into the radiator. Then suddenly I was hitting 235. Bought a Mopar radiator, compared it to the old one and found that the aftermarket radiator had 20% fewer tubes. That basically implies that the Mopar radiator has at least 20% more capacity than it needs in normal passenger car conditions in order to still be adequate on desert rock crawling trails, sustained grades at high temperature and elevation, winch blocking airflow, and many years worth of corrosion and contamination.

Also...are you relying on the gauge to judge your temp? It's not linear. If you're thinking it's 220 based on the gauge, an OBD2 scanner reading live data will probably tell you it's 235.
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Old 07-19-2019, 01:04 PM   #26
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Did you say the replacement water pump was OEM? Years ago, I replaced a water pump on my car ( not a Jeep ) with an rebuilt aftermarket pump. It worked fine until it got hot outside. Then I started having over heating issues like the ones you are describing. After fussing with it for almost 2 years, I replaced it with a new OEM unit. It was then that I noticed that the impeller on the rebuilt unit wasn't fully pressed onto the shaft. It was on enough to fit without issue, and circulated enough coolent for most days. But when it got hot outside, there just wasn't enough flow to keep the engine cool.

Installed the OEM unit and had zero issue from then on. Now I ONLY use new OEM parts on all my cars. It's just not worth the hassle.

In any case, you may want to consider removing and inspecting you water pump. Just to be sure the impeller and case are working as expected.
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Old 07-19-2019, 01:24 PM   #27
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Yes thanks 210 that's why its straight up on the gauge. But now that you know everything what do you suggest ?

We are just trying to help you.


The initial problem with the spike was likely just the parts-store brand thermostat sticking shut. That is why most around here recommend only Stant or Mopar, they are proven to be reliable.


Your comments about adding a lower rated thermostat suggest you might need to do some reading on the cooling system operation.


There are many people on here that wheel in the desert, and the factory Mopar radiator works great for them.
Aftermarket rads are known to not have the same cooling capacity.
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Old 07-20-2019, 03:17 AM
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Thanks for all the replies. It sounds like I need a new radiator. I'm just not sure if the one I have is mopar are not. I guess it's old enough anyway.
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Old 07-20-2019, 04:16 AM   #29
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I'm going to try royal purple ice. Heat index 105 today. If this doesn't help I see a bigger radiator in the future
All Royal Purple Ice will do is lighten your wallet. Water Wetter, Ice and the like are best used in racing applications were only straight distilled water is used. Yes they say it can be used with coolant, but its real purpose was to be run with straight distilled water, to raise the boiling point.

With regard to a thermostat I often read and hear about people suggesting running a 160F or 180F thermostat instead of a 195. A thermostat does not regulate the maximum temperature an engine will run at, or the maximum temperature an engine can reach. All going with a lower thermostat can do is delay, slightly, the maximum temperature an engine will reach, it will not lower it. If an engine is overheating there is something wrong, EG: a bad thermostat, fan clutch, electric fan, radiator, etc. Even an air pocket trapped in the head or block [typically from working on the cooling system and not bleeding it properly] can cause overheating. Or the engine is being overworked, as in off-roading in extremely hot temperatures, or towing more than the rated capacity in extreme heat. Even overworking an engine in cooler temps can over heat it, if it is overworked long enough.
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Old 07-20-2019, 12:29 PM   #30
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A 185 thermostat opens at 185 degrees and a 195 thermostat opens at 195 degrees. So which one is a cooler thermostat? Also the OEM radiator is a single core, but the cores are larger allowing for greater flow through, and cooling. Try having your radiator "Rodded Out" first if it is not too old.

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