2015 Wrangler 3.6L - Blown Head Gasket?

[explorer2030]

2015 Jeep Wrangler 3.6L V6 with 170K miles. I heard some gurgling sounds in the heater core a couple times upon starting the vehicle at work, so I decided to pull the radiator cap even though the coolant level in the overflow bottle was above min. There was no visible coolant in the radiator, and it probably took around a quart to refill. The bottom of the radiator cap and the radiator neck were covered fairly thickly in black particles that would smear when wiped off with a cloth. I am not sure how long the radiator was low on coolant, because the last time I had the cap off was around two years ago. I did have to refill the overflow bottle several times over the course of that period.

I have been driving it to work after I refilled and bled air from the system, and I am finding that the level in the radiator drops around 1 inch below the radiator neck after each drive, the overflow bottle has a higher level, and some of the black particles return under the radiator cap. I decided to pressure test the cooling system hot and also perform a block test. The test fluid turned a greenish color during the block test after 1 min, and I lost about 1 psi in 2 mins and 4 psi in 10 mins during the pressure test. I have identified a small pinhole leak in the radiator on driver side, so I believe that coolant is being pushed out to the overflow bottle and not getting drawn back into the radiator upon cooldown.

My main concern is the returning black particles under the radiator cap and the fluid color change during the block test. The instructions say the fluid should turn yellow, but I am seeing that it is more like a light green. When running the test I would squeeze the bulb, and it would stay like that for about 20 seconds when some air bubbles would come up through the tester to reinflate the bulb. I would squeeze the bulb again and it would repeat, but each time this happened you could start to notice the color change. Does this definitively indicate that I have a blown head gasket, and what I am seeing on the radiator cap is soot from combustion gas getting into the cooling system? The engine has never been overheated based on the coolant temp gauge, and if I monitor coolant temp with my scan tool while driving it will fluctuate in the normal range between 200-209.

 

[Bailey28]

Fixing the pinhole leak in the radiator will allow you to see if all of the coolant in the overflow is being drawn back into the system after shutdown.

The cap could be bad too.

Do you have a second vehicle you can run the fluid test on to see if it changes colors the same way?

 

[PontiacHO]

Hard to say. I’d be inclined to try some stop leak at this age-mileage.

 

[Cousin Vinny]

I would squeeze the bulb again and it would repeat, but each time this happened you could start to notice the color change. Does this definitively indicate that I have a blown head gasket, and what I am seeing on the radiator cap is soot from combustion gas getting into the cooling system? The engine has never been overheated based on the coolant temp gauge, and if I monitor coolant temp with my scan tool while driving it will fluctuate in the normal range between 200-209.

View attachment 349701 View attachment 349702

As best I know, this color change indicates the presence of exhaust gasses in your cooling system. I am not aware of an instance where that would be considered normal, so this color change would concern me.

If you want absolute confirmation of this, you could put the tester bulb by the tailpipe and see if it changes color the same way.

Does the level stay even or does it "volcano" with the level up to the neck and cap off, starting it on a cold start?

 

[Kira]

Cooling systems are screwy things. I sure ain't no expert.
Since you have a radiator leak, maybe fix that first? Does not a pinhole indicate the rest of the radiator is weak?
Then do a compression check?
I'm just thinking of things to check before resorting to leak stop.
Does the 3.6 have a track record of failed HGs?

 

[Lubener]

Fix the leak(s) first. Then I would pressure test the cooling system. When my engine head gasket blew, pressure from the combustion chamber forced a lot of coolant out towards the bottle and it then overflowed. It eventually blew coolant into the combustion chamber of one cylinder causing the engine to hydro lock in my driveway.

 

[NibbanaBanana]

I have a small leak at the water pump in the Chevy Aveo, 272K miles, due to corrosion of the block. About a cup or 2 every week or so. Ended up adding 4 crushed Bars Leak tablets. Completely solved the problem. This car's done with coolant changes.

 

[mk378]

The radiator has to be emptied out some before running a block test. If it's completely full, coolant will come out and mix with the test fluid.

 

[vssjim]

just make sure it is not sucking in coolant if it is only air for sure then you have a problem starting as it will not change any color if all is ok

 

[slacktide_bitog]

If you already know the radiator is leaking, fix that first before doing anything with the head gasket.

You could also try a head gasket sealer like Bars Leaks HG-1 or Blue Devil Pour N Go

 

[explorer2030]

I don’t have a second vehicle to run the fluid test on, but I just bought the bottle of test fluid brand new.

I removed enough coolant so the level was about 3 inches below the radiator neck before doing the block test. I repeated the test 2 more times with the same result and confirmed the coolant never rose high enough to be drawn into the tester.

I originally identified the pinhole leak a couple years ago from some dried coolant residue on the radiator, so I bought a new radiator, hoses, water pump and thermostat at that time. I never got around to installing them because the pinhole leak never seemed to cause any major problem. The coolant temp gauge always stayed normal, I didn’t get the black gunk under the cap at that time, I didn’t have any other engine performance issues, and it passed a pressure test with no loss for 2 mins. The only issue was that the coolant level would drop below min in the overflow bottle occasionally.

I am not sure what to do next because I don’t want to install all these new OEM cooling system parts if they are going to end up coated in this black gunk coming from a blown head gasket. I also don’t want to try adding stop leak in the cooling system unless I sell the vehicle soon. I would sell the parts if I don’t keep the vehicle.

The coolant doesn’t volcano out of the radiator if I run it with the cap off. I ran it up to 212F with a spillproof funnel to purge the system after refilling the low radiator, and the level just gradually rose in the funnel with some bubbles coming up occasionally.

I am not sure if a failed head gasket on the 3.6 is common overall, but I have come across many posters on forums who say they had it happen.

 

[D60]

Not sure what to say about the "black gunk" unless it's engine oil.

My understanding also is that any color change indicates the presence of exhaust gasses. Also false negatives certainly happen but I think false positives don't -- I could be wrong on this.

Personally I have found light shone through the fluid to be helpful:

D

Thread 'Block test -- combustion gases'

Jun 7, 2024

I was recently playing around with an EJ25 (so we all know the outcome) but thought I'd point out the block testers are kinda difficult to read -- or at least it was for me.

Also, I realize the accuracy of these is questionable and even hotly debated in some circles. If you want a hot debate....well, I don't care that much.

Take note of how the fluid begins:

I swore I saw the fluid become lighter during the test, but it still has a light blue hue to the eye. It's supposed to turn yellow if positive. I found using a light helped to show contrast to the...

• D60
• Replies: 7
• Forum: Mechanical/Maintenance Forum

• 

 

[6.7 CTD]

If you are positive you did not draw any coolant into the tester, then yes, you very likely have a small head gasket leak. If I’m not mistaken, the fluid will turn from blue to green for a small head gasket leak or a diesel motor with a blown head gasket. It would turn yellow if it was severe gas engine HG leak. Been in your shoes. Wish you the best of luck with this.

 

[explorer2030]

Not sure what to say about the "black gunk" unless it's engine oil.

The particles/gunk adhere to the radiator cap and smear black on a cloth, but if I dip a rag in the coolant it still looks purple not discolored. The oil in the vehicle looks light amber, so I would assume that the coolant and particles/gunk would look more brownish/yellow if this was due to oil leaking in the cooling system. Wouldn't these jet black particles/gunk indicate soot or carbon being pushed into the cooling system from the combustion chamber? Below is a closeup of one of the larger particles that was floating in the coolant. I never saw this black stuff in the cooling system before the radiator was run low on coolant.

 

[Trav]

Not sure what to say about the "black gunk" unless it's engine oil.

My understanding also is that any color change indicates the presence of exhaust gasses. Also false negatives certainly happen but I think false positives don't -- I could be wrong on this.

Personally I have found light shone through the fluid to be helpful:

D

Thread 'Block test -- combustion gases'

Jun 7, 2024

I was recently playing around with an EJ25 (so we all know the outcome) but thought I'd point out the block testers are kinda difficult to read -- or at least it was for me.

Also, I realize the accuracy of these is questionable and even hotly debated in some circles. If you want a hot debate....well, I don't care that much.

Take note of how the fluid begins:

I swore I saw the fluid become lighter during the test, but it still has a light blue hue to the eye. It's supposed to turn yellow if positive. I found using a light helped to show contrast to the...

• D60
• Replies: 7
• Forum: Mechanical/Maintenance Forum

• 

+1 Unless combustion gases are actually getting into the cooling system you can easily get a false negative if it is leaking anywhere else like an oil return hole or external leakage. Like you I never heard of or seen a false positive, if it turns yellow there is CO in the cooling system from either a bad HG or crack in the head or block.
An articulating borescope down into the cylinder looking up at the valves with the piston at the bottom and the cooling system under pressure you will be able to see the exact area of the leak.

 

[explorer2030]

+1 Unless combustion gases are actually getting into the cooling system you can easily get a false negative if it is leaking anywhere else like an oil return hole or external leakage. Like you I never heard of or seen a false positive, if it turns yellow there is CO in the cooling system from either a bad HG or crack in the head or block.
An articulating borescope down into the cylinder looking up at the valves with the piston at the bottom and the cooling system under pressure you will be able to see the exact area of the leak.

The kit I used is Block Tester brand and the instructions say that the fluid should turn yellow if a combustion leak is present, and yellow-green in diesel engines. Is the fact that my fluid turned green not yellow in a gas engine still a definitive indication that there is a combustion gas leak into the cooling system?

 

[D60]

The kit I used is Block Tester brand and the instructions say that the fluid should turn yellow if a combustion leak is present, and yellow-green in diesel engines. Is the fact that my fluid turned green not yellow in a gas engine still a definitive indication that there is a combustion gas leak into the cooling system?

Not sure how credible this guy is but he says green means small leak, as mentioned earlier in this thread.

The comments are full of others who also saw green on a gas engine, so if it's any consolation, you're not alone.