2016 JKU Cooling Issues Bubbles in Cooling Reservoir


New Member
Mar 11, 2023
Hi friends

I searched my issue on the forums (looked for maybe 10 minutes to be perfectly honest) but couldn't find anything that quite matches up to my scenario.

My Wrangler is a 2016 JKU, 85k miles, no mechanical modifications.

So June of 2022 I was going up a mountain, and noticed my coolant temperature was at 3/4. Went back down the mountain, checked my reservoir, to my horror it was empty. I filled it up with 50/50 and drove home 2 hours back home with no major issue, but I noticed my temperature gauge stayed at literally just a hair above 1/2. Which it didn't used to do post this one issue. I immediately got it tested for coolant leaks, leak down test and compression test at a trusted mechanic, and all tests came back negative. Over the next few months I had random 1 off incidents where my temperature gauge would climb back to 3/4 again but quickly come back down. I had to top off coolant at least twice more after noticing the levels going down.

I gave up on trying to find the problem.

Then in December 2022 the fateful Oil Filter Housing took a poo and I had that replaced with the Dorman Upgraded part. After getting my jeep back from the mechanic for that my mechanic pointed out that the random 3/4 coolant temp thing happened to him while he test drove my jeep after the filter housing replacement. Since it was already at the mechanic, I had my mechanic change the following parts:
Engine fan, Radiator, Thermostat, Fan Relays. and I changed the radiator cap myself.

None of these helped, my temperature gauge still read at just a hair above 1/2 and the occasional 3/4 jump.

Today I had the 3/4 jump again, and I decided you know what its time to go check the coolant level again.

When I looked in my reservoir, with the engine still running after about driving for 1 hr, I saw bubbles coming up, not like a rapid boil, but still a little faster than just the cooling system self burping.
I checked my oil dipstick, oil looks fine. My exhaust doesn't smell sweet, and there is no magic white smoke. I can't find any noticeable leaks anywhere.
The bubbles make me think head gasket, but other than this new development, all the other systems have been there for 9 months, and these other symptoms were there when my engine passed the leak down, and compression test. The CEL didn't come on.

I have not noticed any change in performance, or gas mileage, so I really have a hard time believing it could be a head gasket.

Also when I say occasional 3/4 jump I mean once in a while (1 week plus). So extremely occasional.

Any ideas on what to check or do? My mechanic and I are at a loss.

thanks in advance.

Edit: This issue has had me scared to go wheeling or travel very far out of town which are all things I enjoyed before this issue presented itself

Edit 2: Forgot to mention, it doesn't look like my coolant level in the reservoir went down at all which I suppose is a good thing. I haven't had to top it off since my oil filter housing replacement and no noticeable coolant leaks since.
Last edited:


Staff Member
Lifetime Supporting Member
Feb 22, 2020
Huntington In
I would try changing the t-stat and flushing the system out good. Also could be possible that you have a small air pocket trapped in the system.

Jack the front up at least 6" and take cap off then just let it idle, add coolant as it starts dropping.


Maple syrup season.
Lifetime Supporting Member
Sep 11, 2020
Muskoka Canada
If I made a drinking game for all these persons who or whom join the forum with there problems, Never to see them again. I would be Pissed. Apologies Chris, Home Brew.
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