Proper rad pressure test procedure? 2004 Yukon 6.0

[chevy529]

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?

 

[Matahoe]

I went through the same ordeal. You will want to get an oil analysis to check for antifreeze in the oil. If the test comes back positive then you have a crack in the cylinder head more than likely.

 

[Doubeleive]

ya if it's not on the ground or under the bottom of the overflow tank, radiator or engine then it's burning it, I would take a good look under the radiator and under the water pump area

 

[chevy529]

I went through the same ordeal. You will want to get an oil analysis to check for antifreeze in the oil. If the test comes back positive then you have a crack in the cylinder head more than likely.

Do I understand that on yours it was in the oil but not enough to turn it milky or collect on the oil cap? Did the analysis give you a %? Or just acknowledge a trace?

ya if it's not on the ground or under the bottom of the overflow tank, radiator or engine then it's burning it, I would take a good look under the radiator and under the water pump area

Not ANYWHERE I can see. Which is why it has me baffled. One thought was maybe it's leaking at the back of the motor onto the exhaust once it's warmed up on the highway. Which I don't do often.

Thank you for your thoughts. I'll probably buy an analysis kit after Xmas. Cant hurt.

One more thing making me crazy... er

 

[Doubeleive]

Do I understand that on yours it was in the oil but not enough to turn it milky or collect on the oil cap? Did the analysis give you a %? Or just acknowledge a trace?



Not ANYWHERE I can see. Which is why it has me baffled. One thought was maybe it's leaking at the back of the motor onto the exhaust once it's warmed up on the highway. Which I don't do often.

Thank you for your thoughts. I'll probably buy an analysis kit after Xmas. Cant hurt.

One more thing making me crazy... er

my engine was burning coolant at about a rate of 1qt a week @242k, one way to tell is to pull your oil fill cap off and look under it if it looks milky at all then its probably what is happening, some say a little moisture is ok but on a normal operating motor I have never seen a lick of moisture under the oil filler cap

 

[chevy529]

my engine was burning coolant at about a rate of 1qt a week @242k, one way to tell is to pull your oil fill cap off and look under it if it looks milky at all then its probably what is happening, some say a little moisture is ok but on a normal operating motor I have never seen a lick of moisture under the oil filler cap

Ive only put about 5000km\3000 miles on in 9? months and it doesn't use anywhere near the amount you were experiencing. I'm just old and picky

Yeah, there are a few standard ways to check for coolant loss. Smell the exhaust, check under the oil cap, check under the rad and water pump\front of engine. If it's in any of those areas it isn't apparent to me.
I almost wish it was as it would be obvious. Then I could just get it fixed.

THIS? This will drive me batty till I find it lol

 

[Doubeleive]

my nose has never been so good to smell much more than a fart so that method never worked for me, lol but I have had a tiny pin hole in a hose before that was rather hard to detect at first. only other place I can suggest to look is the rear heater core which is underneath behind the passenger wheel/passenger side, that is where the 2 hose that go into the firewall come out and go back in.

 

[Matahoe]

Do I understand that on yours it was in the oil but not enough to turn it milky or collect on the oil cap? Did the analysis give you a %? Or just acknowledge a trace?

It just said POS for POSITIVE. It's a determination based upon certain elements in the oil like silicon, boron, sodium, etc. What lead me onto it was a clear sweet tasting condensate on the underside of oil cap. Not scientific but what else can be sweet tasting in an engine? Definitely not the oil itself.

 

[chevy529]

It just said POS for POSITIVE. It's a determination based upon certain elements in the oil like silicon, boron, sodium, etc. What lead me onto it was a clear sweet tasting condensate on the underside of oil cap. Not scientific but what else can be sweet tasting in an engine? Definitely not the oil itself.

I see.
Thanks for that. I was curious as I've had analysis done on many units in the past (trucks and equipment) and they never came back positive for coolant in the oil. But I didn't expect it (or ask for it) either. I was more concerned with wear. IE: metals

There are no normal signs of coolant in the oil but an analysis may be in order as a way to definitely rule some things out.
Thanks

 

[Matahoe]

Yw. Could also be a bad head gasket or slow leaking radiator or heater cores if no antifreeze shows up in analysis. I also talked to my local machine shop a few months back about the castech issue. They said that sometimes the crack(s) in the head are so fine that it won't start to leak until the engine/head is hot enough. I also asked about welding the head to fix it. Unfortunately there is no way to permanent weld cast aluminum. It will just crack again under the tty bolt compressive forces. But yeah probably time for an oil analysis. Having antifreeze in the oil kind of rules out a bunch of other possibilities so it's a good starting point.

 

[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!