Need second opinions on 2002 TJ 2.5 (possible blown head gasket)

TJistheway

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Mar 28, 2023
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Knoxville, TN
Hey guys – looking for some insight before I dive into this.

Background:
I’ve got a Jeep I’ve owned since 2009, with a 2.5l 4 cyl and about 120k miles on the motor I had installed in 2012. It’s always run pretty well (untill it doesnt), but lately, it’s been showing signs of something going wrong.

Over the last few weeks, I’ve noticed a few red flags:

It’s been sporadically losing coolant, but there are no visible leaks and nothing hitting the ground.

Oil looks clean (no milkshake), but I’ve had occasional rough starts and unstable idle.

It’s also been running hotter than normal, creeping well past 210°F and into the 230s, especially during last week’s heat wave (mid-90s).


Then a few days ago, I was on the interstate with the A/C on (cue 4-banger jokes), and the temp gauge spiked into the red. I killed the A/C and got off the highway, and weirdly, the temp dropped back down really fast, even without turning the heater on. When I stopped, I popped the hood and saw the coolant reservoir boiling, which I’ve never seen it do.

I checked the oil again after the incident – still not milky, but it was critically low. I’m thinking oil might be getting into the cooling system, lowering the boiling point, even though there’s no obvious mixing.

At this point, I’m suspecting a failing head gasket—maybe just starting to go. But before I jump into my first head gasket job based on a hunch, I’d love some second opinions.

I do all my own wrenching and I’m only slightly afraid to tackle it, but here are the other things I’ve considered:

Bad radiator cap – changed it with a new one

Bad radiator – replaced 2023 posible but unlikely bc it doesnt explain the oil loss

Thermostat sticking – unlikely, installed a Robertshaw 330 series hi flow balanced sleeve thermostat when i did the radiator in 2023

Water pump failing – possible, replaced in 2023. Does not explain the oil so unlikely.


What do you guys think? Should I go ahead and start prepping for a head gasket job, or is there something else I should rule out first?

If I go through with it then I will read through previous posts about the pitafalls. Im sure others have had this happen.

I should add that it still runs and i could drive it but im not. Im already afraid i did damage running it low on oil and it overheating.

Shes my baby though, I just cant let her go. Appreciate any input.
 
Perhaps. Im learning, used to take it somewhere for major stuff. That said, I'm kind of afraid to run it that long at this point with the oil loss though. Shouldn't I do something that doesn't run the risk of making things worse? Or just add oil and crank it long enough to test?

Edit: my bad apparently I didnt know what a leak down test was lol. Disregard. I will learn how to perform the test chris thanks man.
 
Perhaps. Im learning, used to take it somewhere for major stuff. That said, I'm kind of afraid to run it that long at this point with the oil loss though. Shouldn't I do something that doesn't run the risk of making things worse? Or just add oil and crank it long enough to test?

A leak down test is a diagnostic procedure used in automotive repair to assess the condition of an engine's cylinders by measuring the amount of compressed air that leaks out of them. It's a more detailed method than a compression test, helping to pinpoint the source of compression loss. The test involves introducing pressurized air into a cylinder (with the piston at top dead center) and then measuring how much air leaks out and where it's leaking from.
 
@Wildman @Chris

Can one of you gents recommend a leakdown tester that for sure comes with the right adapter for the sparkplug holes in the 2.5l? I was going to get the OTC 5609 https://www.amazon.com/dp/B0030EVL60?tag=wranglerorg-20
But reviews say spark plug adapters for the 4.0 arent long enough.

I never had to do any serious maintenance on my 2.5 so I don't know which leakdown tester would work or not work. I don't even think I ever ran a compression test on my engine.