Head gasket diagnosis help

Hello y’all. My 2008 Tacoma with 263k miles started making a gurgling sound from behind the dash. I tried to bleed air out twice but it continued. The. Plant also appeared to be going into the overflow and NOT going back to the radiator. Every time I checked I the radiator was low. Coolant pressure test revealed it lost 4-5psi overnight full of coolant and even more with the radiator drained.

I scoped the cylinders and #6 was full of oil due to the valve cover gasket BUT it appeared coolant showed up. What do you guys think
That night
The next morning


I have NOT been able to re create the coolant on the cylinder walls. Compression/leak down test were perfect and there was no bubbles in the coolant with shop air pumped into the cylinder, however there IS bubbles at idle with the truck on. Blue fluid block tester was negative as well

 

Whats the oil look like?

 

Wasn’t sure if it was bubbles from the oil or coolant.

 

Oil looks fine. Just changed it recently too

 

Are those bubbles of coolant on the cylinder bore in the scope view?

 

Also, how did the spark plug for that cylinder look? Was it too clean compared to others?

 

If you are able, Id run a compression check.

 

I see the coolant intrusion, looks more like water, but so be it.....'
It's done....

I also wouldnt focus on the psi drop, youre going to get some bleed-down past the pressure tester over time...
Theyre not 100% sealed on a long soak, they will bleed down unless 100% brand new quality tool...

 

Did you scope with the radiator under pressure? My coolant loss was minimal over time but I was still able to see an occasional drop of coolant roll down the cylinder wall while under pressure.

Btw, that looks like moisture or coolant as opposed to oil.

 

Its clearly both...
pic #1, oil running down cylinder wall
pic #2, coolant....

 

I was just asking. Been down this road before. If it's that clear, then there is a head gasket issue. No grey area there.

 

absolutely!
Coolant is getting into the cylinder from the pics, very clear, 100% without any doubt...

 

Yes. I have never been able to replicate it after that first time and I never saw the coolant run. Just when I checked it overnight. I figured it would be pink. I think all signs are pointing toward the head gasket for sure

 

I agree with you just got puzzled when I’ve tried to replicate it multiple times even overnight pressure tests and haven’t seen any coolant. I guess im lucky I even caught those first pics

 

get it hot & then put the PT on it overnight....
You can crank the pressure up to 20-25max in the morning if you dont see anything, that shouldn't really hurt anything.
But looking at your pics, it's very clear that you do in fact have intrusion. The clear water droplets running down the side of the cylinder walls...
Sometimes its difficult to position the boroscope so you can get a clear shot of where the head, head gasket, & block meet.
Its usually the inside edge that leaks so look there, if youre going to look again.

 

I tried that last night and nothing this morning. Tried 100psi in the cylinder and no bubbles, yet bubbles when at idle and running. I think there’s no other explanation for the bubbling radiator, gurgling sound behind the dash, and the coolant not being sucked back into the radiator

the coolant, in my opinion, smells like exhaust despite the negative block test

 

Block test is very inefficient test when the gaskets aren't completely blown-out....
You put 100psi in the questionable cylinder & youre certain both valves were closed?
The coolant level in the radiator didnt rise???

 

I put 100 psi with both valves were closed to do the leak down test but had an issue with the hose leaking so I did the leak down at 70. I tried 100 psi of shop air with valves open as well and neither had a rise OR bubbles in the radiator.

the suspect cylinder