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.
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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.
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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