Exshaust Gases in coolant system. - The 1947 - Present Chevrolet & GMC Truck Message Board Network

Bob Hinz · 08-26-2002, 05:00 PM

Have a 454 engine that seems to be building up a lot of pressure in the coolant system. took the heads off and had them checked and still have that same problem. Doesn't appear to be over heating as far as I can tell. Put on a new Termostat, water pump, hoses just for GP's. I was told that the block was bad and I was getting exshaust gases in the coolant system, but I have a hard time with that. The oil is clean and when I had the heads off, there was no evidence of coolant getting in to the oil. Using a 13 psi Radiator cap, maybe need a larger one? Help!!

jku72 · 08-26-2002, 05:10 PM

If cracked, it is quite possible to get exhaust gasses into the water, but not have water in the oil. If the crack is small enough, a firing pressure of 500psi is a lot higher than 13 psi in the water system. The 13 psi may not be strong enough to force water through the crack(if there is one) but the 500psi is certainly strong enough to push air into the water. These can be hard to find.
But, hot spots can cause local boiling and overpressure as well, boiling it over. Anyone who ever owned a pontiac can verify this.
Check everything first, but there could be a crack.

Bob Hinz · 08-26-2002, 05:14 PM

What's causes hot spots and local boiling?

ChevLoRay · 08-26-2002, 05:16 PM

There are smarter people on here than me, but here is my 2-cents worth.

Get one of those cooling system pressure testers like the shops and stations use. Put it on your radiator, as if you were going to check the cooling system for leaks. Heck, go ahead and pressurize it before you do the following. After you have pressure-checked the cooling system, and you've tightened all of the loose hose clamps, fire it up. Leave the cap on the radiator. As the engine comes up to operating temperature, watch the pressure gauge. I'm going to guess that combustion gasses (which are hot) will leak into the coolant and drive the pressure upwards, past the normal point. There is more to this procedure than I remember, so maybe some of the others will help.

Water doesn't have to get into the oil, nor does oil have to get into the water, for you to have a problem. If the head gasket is blown, you can have the problem. Likewise, if there is a problem with the block or the heads (and you ruled-out the heads), then you could see the problem when the gasses (bubbles) appear in the coolant. I don't see how you could be losing compression into the coolant, without seeing the engine overheat. If you aren't getting oil in the coolant, and you aren't getting coolant in the oil, and you're getting compression gasses in the coolant, it should be relatively easy to figure out where the problem is, or could be. It make take magnafluxing the heads and the block to isolate the problem. Good luck.

*Zkast* · 08-26-2002, 08:10 PM

What leads you to believe there is too much pressure?

If you think there is possible combustion gases getting into the cooling system there are a few ways to check this.
Preferred method:
Find a local automotive repair shop that has a 4 or 5 gas analyzer. Have them run a check on the recovery tank and cooling system. If they have never done this? Ask them to try... look for HydroCarbons. Normal will be 0 - 10 ppm (parts per million), If you see numbers upwards of 50 - 1000ppm then you most definatly have a Head/block problem allowing combustion gases into the system.

The other way (less accurate) is whats called a block test.
It uses chemicals to check for hydrocarbons in the coolant. Beware though, i've seen cars with HC's over 200ppm pass this type of test and blow the coolant out after a few minutes on the highway.

Can you give a little more info on why you think there is a problem? Maybe there is more to this than meets the eye.

Bob Hinz · 08-29-2002, 12:49 PM

Had somebody else look at it. A combination of timing and carb problems. The exhaust headers would glow after at running for 5 minutes. Got it all fix and it runs great now. Thanks for all the help.

**StingRay** · 08-29-2002, 03:15 PM

I have a real good buddy that has a rad shop that without a word of lie can sniff out hydrocarbons in antifreeze with his nose. Some good experienced rad guys develope the talent over the years so try a good rad shop. They usually have mechanical/electronic sniffers as well but the nose is cheaper and in my buddy Darrens case more reliable.

08-26-2002, 05:00 PM	#1
Bob Hinz Registered User Join Date: Aug 2002 Location: Maine Posts: 6	Exshaust Gases in coolant system. Have a 454 engine that seems to be building up a lot of pressure in the coolant system. took the heads off and had them checked and still have that same problem. Doesn't appear to be over heating as far as I can tell. Put on a new Termostat, water pump, hoses just for GP's. I was told that the block was bad and I was getting exshaust gases in the coolant system, but I have a hard time with that. The oil is clean and when I had the heads off, there was no evidence of coolant getting in to the oil. Using a 13 psi Radiator cap, maybe need a larger one? Help!! __________________ Bob Hinz

08-26-2002, 05:14 PM	#3
Bob Hinz Registered User Join Date: Aug 2002 Location: Maine Posts: 6	What's causes hot spots and local boiling? __________________ Bob Hinz

08-26-2002, 05:16 PM	#4
ChevLoRay Old Skool Club Join Date: Jun 2001 Location: Benton, AR "The Heart of Arkansas" Posts: 10,880	There are smarter people on here than me, but here is my 2-cents worth. Get one of those cooling system pressure testers like the shops and stations use. Put it on your radiator, as if you were going to check the cooling system for leaks. Heck, go ahead and pressurize it before you do the following. After you have pressure-checked the cooling system, and you've tightened all of the loose hose clamps, fire it up. Leave the cap on the radiator. As the engine comes up to operating temperature, watch the pressure gauge. I'm going to guess that combustion gasses (which are hot) will leak into the coolant and drive the pressure upwards, past the normal point. There is more to this procedure than I remember, so maybe some of the others will help. Water doesn't have to get into the oil, nor does oil have to get into the water, for you to have a problem. If the head gasket is blown, you can have the problem. Likewise, if there is a problem with the block or the heads (and you ruled-out the heads), then you could see the problem when the gasses (bubbles) appear in the coolant. I don't see how you could be losing compression into the coolant, without seeing the engine overheat. If you aren't getting oil in the coolant, and you aren't getting coolant in the oil, and you're getting compression gasses in the coolant, it should be relatively easy to figure out where the problem is, or could be. It make take magnafluxing the heads and the block to isolate the problem. Good luck. __________________ Member Nr. 2770 '96 GMC Sportside; 4.3/SLT - Daily driven....constantly needs washed. '69 C-10 SWB; 350/TH400 - in limbo The older I get, the better I was.

08-29-2002, 12:49 PM	#6
Bob Hinz Registered User Join Date: Aug 2002 Location: Maine Posts: 6	Had somebody else look at it. A combination of timing and carb problems. The exhaust headers would glow after at running for 5 minutes. Got it all fix and it runs great now. Thanks for all the help. __________________ Bob Hinz

08-29-2002, 03:15 PM	#7
StingRay Senior Member Join Date: Mar 2000 Location: Saskatoon,SK,Canada Posts: 2,476	I have a real good buddy that has a rad shop that without a word of lie can sniff out hydrocarbons in antifreeze with his nose. Some good experienced rad guys develope the talent over the years so try a good rad shop. They usually have mechanical/electronic sniffers as well but the nose is cheaper and in my buddy Darrens case more reliable. __________________ Saskatoon, Saskatchewan Canada

08-26-2002, 05:10 PM	#2
jku72 Registered User Join Date: Jan 2002 Location: cornville, maine Posts: 659	If cracked, it is quite possible to get exhaust gasses into the water, but not have water in the oil. If the crack is small enough, a firing pressure of 500psi is a lot higher than 13 psi in the water system. The 13 psi may not be strong enough to force water through the crack(if there is one) but the 500psi is certainly strong enough to push air into the water. These can be hard to find. But, hot spots can cause local boiling and overpressure as well, boiling it over. Anyone who ever owned a pontiac can verify this. Check everything first, but there could be a crack.

08-26-2002, 08:10 PM	#5
Zkast Account Suspended Join Date: May 2002 Location: Olathe, Kansas Posts: 929	What leads you to believe there is too much pressure? If you think there is possible combustion gases getting into the cooling system there are a few ways to check this. Preferred method: Find a local automotive repair shop that has a 4 or 5 gas analyzer. Have them run a check on the recovery tank and cooling system. If they have never done this? Ask them to try... look for HydroCarbons. Normal will be 0 - 10 ppm (parts per million), If you see numbers upwards of 50 - 1000ppm then you most definatly have a Head/block problem allowing combustion gases into the system. The other way (less accurate) is whats called a block test. It uses chemicals to check for hydrocarbons in the coolant. Beware though, i've seen cars with HC's over 200ppm pass this type of test and blow the coolant out after a few minutes on the highway. Can you give a little more info on why you think there is a problem? Maybe there is more to this than meets the eye.



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