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Discussion Starter · #1 ·
Hi all I'm new to the forum but been a long time lurker.

A couple months ago my 2015 JKUR with 40,000 miles started to show signs of overheating, or heating up more than usual if that's the right term. I know there are a million threads about this issue and it can be caused by the simplest stuff like a bad radiator cap up to a warped cylinder head.

So I decided to go step by step rather than blindly purchasing components and hoping them to work.

My JK:
-2015 40,000 miles with regular maintenance
-5spd auto with 35's and 4.1
-Mostly city driving and light wheeling, nothing extreme. Never been to serious mudding.

Symptoms:
-Before all of the following my jeep always ran at less than 212F highway and the needle was dead center no matter what, even at pretty serious hill with 4h engaged. Now with the slightest incline i can see the needle moving past 12 oclock position and once it hits 230F it is already midway to the 3/4 mark.
-About 4 months ago started to smell coolant after vehicle was parked and fan was still on
-Coolant level started to drop which never needed refill before, one day I checked and it was below the minimum. Then 1 gallon of coolant was added ass needed over the course of 3 months or so.
-Never gets past 206F while idling or driving at parking lot speeds
-Normal city driving is between 200-220.It's usually higher when AC is off.
-Gets ups to 220-228 range trying to maintain highway speeds 50-60mph
-Easily goes up in the 230 range when going up a hill, even the smallest hills will raise the temps immediately.
-Stop and go traffic where it needs to gain speed and then back to braking can keep temps at 220+ range

Possible Causes and their fix, marked green for those already dealt with, yellow in progress
-Mud between radiator and AC condenser: cleaned with high pressure washer, no mud came out and did not help at all
-After Market grill insert blocking airflow: Drove around without any grill and engine plastic cover removed, did not help
-Blown gasket: checked for engine oil, no signs of milkyness in the oil and levels are fine. Oil pressure also builds up fine according to the digital psi display.

-Radiator cap with bad seal: already ordered new one
-Coolant leaking somewhere: Ordered some OAT compatible UV coolant dye to check for leaks. But at first sight I could not identify any obvious leak.
 

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Discussion Starter · #2 ·
Just realized I cannot edit posts so here's the continued post:


-Thermostat is out of the question since 95% of the time the temperature is already above 203F. Maybe I'm wrong here if so please correct.
-While idling and AC is ON I can see that the fan kicks to high mode

Things I will have to replace if even after the UV dye I can't see leaks, but it must be evaporating or leaking somewhere since I can smell it and it is consuming. To be replaced in order:
1. Thermostat and housing
2. Radiator and maybe the hose
3. Water Pump
4. Check for warped heads, this is the most complicated task and I would like to address the above possible issues before disassembling the engine.
 

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Just realized I cannot edit posts so here's the continued post:


-Thermostat is out of the question since 95% of the time the temperature is already above 203F. Maybe I'm wrong here if so please correct.
-While idling and AC is ON I can see that the fan kicks to high mode

Things I will have to replace if even after the UV dye I can't see leaks, but it must be evaporating or leaking somewhere since I can smell it and it is consuming. To be replaced in order:
1. Thermostat and housing
2. Radiator and maybe the hose
3. Water Pump
4. Check for warped heads, this is the most complicated task and I would like to address the above possible issues before disassembling the engine.
Mine started leaking at the thermostat gasket, just lightly steamed and took a few weeks before the resivour runs out, but was also affecting the thermostat and kicking on the warning light.i took some chalk and marked the base of the thermostat in order to find that it was leaking.
 

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:welcome: to the Forum..:wavey:
 

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What you describe is nearly identical to what happened in my '12 JKU 5 Speed..
In my case I had to get a new heater core.. and about 1 year later, a new radiator after it failed.. when we replaced the heater core we found about 1/4 pound of "putty" in the heater core and radiator that had formed from the previous owner apparently mixing HOAT and OAT coolant.. we did a super-flush of the radiator at that time, but it still failed a year later..
 

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Just realized I cannot edit posts so here's the continued post:


-Thermostat is out of the question since 95% of the time the temperature is already above 203F. Maybe I'm wrong here if so please correct.

-While idling and AC is ON I can see that the fan kicks to high mode

Things I will have to replace if even after the UV dye I can't see leaks, but it must be evaporating or leaking somewhere since I can smell it and it is consuming. To be replaced in order:
1. Thermostat and housing
2. Radiator and maybe the hose
3. Water Pump
4. Check for warped heads, this is the most complicated task and I would like to address the above possible issues before disassembling the engine.
Mine started leaking at the thermostat gasket, just lightly steamed and took a few weeks before the resivour runs out, but was also affecting the thermostat and kicking on the warning light.i took some chalk and marked the base of the thermostat in order to find that it was leaking.
Did it look like this after it leaked underneath your jeep?
 

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Discussion Starter · #7 ·
Thanks for the suggestion, since we have no way to examine near the thermostat housing I guess it will be the first thing to be replaced if the UV dye fails to show any leak as well. I have read lots of case where a cracked housing will slowly leak coolant and get evaporated instantly.

We lifted the car and inspected underneath and could not find any signs of orange-pink coolant drip anywhere, I bought my JK second handed at just 12k mi and believe the coolant is the stock OAT factory one.

But it HAS to be evaporating somewhere because the smell of coolant evaporating is not the same as coolant being hot when pushing to the reservoir.

One interesting thing that’s happening is that while idle it will go as high as 226F until the fan kicks on at full speed with AC OFF, but with AC ON it will maintain the temp around 200-210 and the fan constantly kicks on at medium speed. Does this tell you something?

When the fan turns on it first wiggles a little bit and then 2 seconds later will start to spin
 

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One interesting thing that’s happening is that while idle it will go as high as 226F until the fan kicks on at full speed with AC OFF, but with AC ON it will maintain the temp around 200-210 and the fan constantly kicks on at medium speed. Does this tell you something?

When the fan turns on it first wiggles a little bit and then 2 seconds later will start to spin
This how mine is acting since new, up to 226 with the AC off
200-210 with the AC on, fan on low speed.
And goes up to 230 when slowly going up the hill.
No leaks, im adding coolant from time to time but not much.
So far 20K miles mostly in temp near or above 100f but noting major, the needle stays in the middle all the time.
Any "prescribed" software updates from the dealer maybe?
 

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Mine sounded similar. Oil cooler replacement fixed it.
 
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I have a 2013 JKU Rubicon with a little over 70,000 miles and I noticed it was over heating too. Originally while I was driving my son to school, I had a check engine and noticed it was overheating. I put a ODBii reader and it mention a temp issue. I replaced the thermostat and housing and burped the system and it cleared the engine light, so I thought everything was good. Then I went turkey hunting and while climbing the mountains, the temp went up again. This time I went to my local auto shop and got a flush and made sure that they used OAT fluid. I noticed the Jeep running a little warm but once the fan kicks on, I thought everything was ok. Later, I noticed that the overflow tank was empty. I added more OAT coolant and burped the system. So, I tried to find the leak but I couldn’t see any leaks, even when it’s below freezing, I don’t see any leaks. I still add fluid and I’m still looking. I haven’t changed the radiator cap so I’ll do that this weekend and hopefully that works. I also noticed that I can smell coolant too. Over the weekend, I took the Jeep on a trip and it started to run hot when the rpms went over 4000, but once the transmission shifted up and rpm went to 3000, it cooled down. I’m stumped!
 

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All, Certainly could be a pin hole leak or other issues. had mine (2015) to the dealer as I smelled fluid, they of course found nothing. depending on your sale date you may still be under the 100k powertrain so take it in maybe they find something.

As for temps the 3.6 runs hot, compared to say the 4.0L.. the fan as noted does not kick in till 226-228.. had mine hit 235 one day and I about had a heart attack as the fan was just not cooling it down. I had installed a small light bar above the winch and that was enough to mess with it. Removed that, and then later mounted the winch down near the frame rails.. Did wonders for putting temps back to stock like numbers, runs low 200's most of the time now where prior it was ping pong of 200 to 228.
 

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Losing coolant is obviously a separate issue. But realize the 3.6 runs warm. Trying to alter it to run cooler actually is not good for the engine.
 

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In theory if you have the common radiator leak that’s all but invisible (noting your coolant loss and smell), that could be causing a pressure loss in the system and consequently there’s less pressure to keep the boiling point down — thus the system is less efficient and will tend to generate more heat. It might be worth doing a pressure test on the system and see if it holds before replacing too many parts.

I agree that the pentastar runs hot and as we all know the fan doesn’t kick in till later, but if you’ve noticed a gradual increase in your average temps and smelling coolant, you’re likely on to something and I agree, it’s a good idea to start working the issue before it gets too bad.




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Expansion bottle is open - when hot it would smell coolant a bit. The bottle also might develop cracks around the conecting tabs.
If rad is full and bottle empty i would first remove and check the bottle for cracks.
And of course one of the possibilities is the famous oil filter housing but how to visually inspect it without removing the upper intake idk.
 

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Just realized I cannot edit posts so here's the continued post:


-Thermostat is out of the question since 95% of the time the temperature is already above 203F. Maybe I'm wrong here if so please correct.

-While idling and AC is ON I can see that the fan kicks to high mode

Things I will have to replace if even after the UV dye I can't see leaks, but it must be evaporating or leaking somewhere since I can smell it and it is consuming. To be replaced in order:
1. Thermostat and housing
2. Radiator and maybe the hose
3. Water Pump
4. Check for warped heads, this is the most complicated task and I would like to address the above possible issues before disassembling the engine.
Mine started leaking at the thermostat gasket, just lightly steamed and took a few weeks before the resivour runs out, but was also affecting the thermostat and kicking on the warning light.i took some chalk and marked the base of the thermostat in order to find that it was leaking.
Did it look like this after it leaked underneath your jeep?
No, that looks like an oil cooler or oil filter body leak. They went plastic on those at some point and are crack sensitive. And not a cheap fix for such a cheap part.
 

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OP, I've chased a similar problem for awhile, without resolution, but have learned a lot:

"Wiggling" fan at startup is normal. These are PWM fans, and the first pulses create the movement you see.

Running cooler with the AC on is normal, and desired. The AC head pressure triggers the fan to come on earlier than engine temp would, and that keeps coolant temps lower under light load conditions.

The thermostat isn't completely off the hook, as it could be not opening fully. Not likely, though.

As someone else mentioned, pressure test first, and post the results here. Look for a leak on the drivers side of the radiator where the aluminum mates with the plastic endcap. Then look for signs of evaporated coolant on the thermostat housing. Also check for a cracked overflow tank, again as others have mentioned.

If you find no leaks anywhere, it's time to pull the intake and check the oil cooler. This is where I am in the process (after doing a bunch of other stuff that had no effect), but haven't had time to tear into it, and won't for a couple more months.

Good luck, and post what you find!

Mark

Sent from my SM-G935V using Tapatalk
 
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