Coolant disappearing

[a64pilot]

Go to an auto parts store and buy the test kit that test for the presence of combustion gasses in the coolant, or order it on Amazon. Don’t buy the electronic ones, all you need is the one with the blue liquid, it changes color if combustion gasses are present, and it’s a dramatic color change, no judgement call here.
Don’t pull the head until you test.

[dennismenace111]

Yep! First thing tomorrow I'll give that a try!

Could a bad o ring on the heat exchanger or a bad internal gasket let coolant into the exhaust and admit air bubbles?

[skipperpete]

Originally Posted by dennismenace111

Yep! First thing tomorrow I'll give that a try!



Could a bad o ring on the heat exchanger or a bad internal gasket let coolant into the exhaust and admit air bubbles?

Anything’s possible but only a low pressure test of the heat exchanger assembly will confirm or deny that theory. A better diagnostic would be to remove the injectors and do a quick leakage test. Just put 100psi into the injector hole ( large diameter hole ) with the piston at BDC and the valves slackened off. Bubbles in the coolant top tank means a leaking gasket or often on 2GMs a crack between the valve seats.

[dennismenace111]

Tried a couple of things today! Redid the pressure test and again, the pressure held steady with the engine off. Started the engine and watched the pressure slowly increase.

Stopped the engine and removed the hose from the heat exchanger to tge exhaust mixing elbow. Pressurized the heat exchanger again and the pressure held and no sea water came out if that hose!

At this point, I think it's pretty conclusive that either the gead gasket is leaking or there is a crack in the cylinder head. No coolant gets into the oil... So I think that the engine block is intact!

I also found that the pressure cap needs replaced as it relieves pressure at around 10 psi..

Does anyone have a shop manual that describes removing the head on a 2GM20F?

[skipperpete]

Originally Posted by dennismenace111

Tried a couple of things today! Redid the pressure test and again, the pressure held steady with the engine off. Started the engine and watched the pressure slowly increase.



Stopped the engine and removed the hose from the heat exchanger to tge exhaust mixing elbow. Pressurized the heat exchanger again and the pressure held and no sea water came out if that hose!



At this point, I think it's pretty conclusive that either the gead gasket is leaking or there is a crack in the cylinder head. No coolant gets into the oil... So I think that the engine block is intact!



I also found that the pressure cap needs replaced as it relieves pressure at around 10 psi..



Does anyone have a shop manual that describes removing the head on a 2GM20F?

I’m hoping that you only have a leaking head gasket but here’s what a cracked head looks like. This was a raw water cooled engine so it didn’t matter that the jacket water was getting a small amount of compression. Nothing tricky about getting the head off apart from the annoying long studs. Probably a good idea to take out the valves for inspection and replace the stem seals while you have the head on the bench for scrutiny.

[Wotname]

Originally Posted by dennismenace111

Tried a couple of things today! Redid the pressure test and again, the pressure held steady with the engine off. Started the engine and watched the pressure slowly increase.

Stopped the engine and removed the hose from the heat exchanger to tge exhaust mixing elbow. Pressurized the heat exchanger again and the pressure held and no sea water came out if that hose!

At this point, I think it's pretty conclusive that either the gead gasket is leaking or there is a crack in the cylinder head. No coolant gets into the oil... So I think that the engine block is intact!

I also found that the pressure cap needs replaced as it relieves pressure at around 10 psi..

Does anyone have a shop manual that describes removing the head on a 2GM20F?

There is one in the CF library which can be downloaded.

https://www.cruisersforum.com/forums...?do=file&id=45

[sailah]

This test is what I used to detect my failed head gasket. You fill up the "turkey baster" with the fluid and insert where your rad cap goes. If it detects combustion gas it changes color. In my case it changed color in 2 secs. I was pushing coolant out of coolant system into overflow tank. Usually a failed head gasket will pressurize the cooling system since the cylinder compression (~350-400psi) is far greater than cooling system pressure at 10-13 psi. I had a slight warp in the head which is why the gasket wasn't working. I had my machine shop check head on surface plate, even though I also have a AA lab plate in my shop. I also had them magnaflux head to check for cracks. The flatness check is simple and cheap. Recommend doing that first and if you find a warp, stop there and surface head. Magnaflux is expensive compared to flatness.

https://www.amazon.com/UView-560000-...1299273&sr=8-4

I also ran a leak down test and determined the leak was coming from cylinder 2-3. Which is exactly what machinist told me when he checked it. Those are fairly cheap and easy to do. You need 120 psi air and a way to rotate crank. It lets you test a whole variety of symptoms depending on where the "leak" is going in each cylinder. If you hear it in intake, bad intake valve. Exhaust? Bad exhaust valve. Bubbles in coolant? Head gasket. Air from oil dipstick? Rings etc.

https://www.amazon.com/OTC-5609-Cyli...s%2C145&sr=8-2

I'd do both those cheap tests before you assume anything else or take anything apart.