Proper rad pressure test procedure? 2004 Yukon 6.0

[Fless]

You can also have the coolant tested for exhaust gases.

 

[chevy529]

You can also have the coolant tested for exhaust gases.

Very cool! TY for the link!

 

[Matahoe]

Just check your overflow bottle for bubbles coming up as you rev the engine slightly up and down at idle. No need for an exhaust gas tester this way. Make sure the engine heats up with the overflow bottle cap off.

 

[UrbanSuburban]

On my 04 Sub, it was the rear line to the rear heater, it was a very tiny leak but over time it would drop, the total level down. One other thing I found was not to use the coolant pressure tester that has the rubber end, it usually always slowly moves up under pressure. The 'Stant' system would go on like a rad cap and stay on properly. I also changed the rad cap. Good luck hunting it down.

 

[retiredsparky]

If you have the rear heater/ac, the two coolant tee connections at the center of the firewall above the motor are prime candidates. O-rings are great inventions for assembly line workers, just plug it together. For long term sealing of hot coolant, not so great. The rubber will eventually shrink and harden enough to cause a leak.

Since your pressure test did not show a leak, I am betting on tiny cracks in one or both of the heads. The cracks allow the coolant to slowly leak into the valve/rocker arm area of the head where it evaporates.

If you google "USB camera with led lighting" you can buy one and stuff it down the oil fill and see if the top of the head on that side has a very clean area around a head bolt. Typical sign of coolant leak.

 

[M1Gunner]

I tried a search but couldn't find anything relevant.

My Yukon has a very slow coolant leak which I'm not finding. It's been decades since I've done a pressure test so maybe, on a modern vehicle, I just didn't do it right.

Started and drove it 9-10 miles to my cousins shop. BS'd a bit then hooked up pump to overflow tank.
Pumped it to 15 psi and let it sit. BS'd some more.

After 15-20 minutes it didn't drop. At all. So I assumed it was fine.

But it's going somewhere. No smell at exhaust either.

Did I just do it wrong?

How’s the terrain in your area? Flat land, hilly?

 

[Matahoe]

I dont want to get too far off track but ....as far as the Castech issue is concerned...my local machinist had a similar story. The cracks can be very fine and unable to see. Head must be checked with a two part penetrant and developer. MagnaFlux is ineffective with non-ferrous aluminum heads.

The Leaking happens under bolt clamping force pressure points where there was poor casting. He also said that the type of head doesn't matter much. It can happen to any production head during the time frame under question. That's goes partially against what is described in the TSB. But I tend to trust his experience more than the TSB.

Sorry for scatter brained description. I'm just throwing out there what I remember from the phone call i had a month or two ago with the machinist.

 

[chevy529]

I wanted to double check before I replied. My 6.0l is the RPO LQ4. The head problems were, from the GMC TSA that I read. Not this engine. Mostly the 5.3/4.8. I'll probably do an oil analysis and dye check just because.
But the comment about the o-rings grabbed my attention. No coolant traces in cab but on rare occasion I can smell it inside. Air is pulled in right close! Thank you for all replies!