Water Pressure Issue

[mdc689]

Current situation.....When I drive my car for any amount of distance it builds water pressure. After a drive the radiator top hose is pretty hard to squeeze. After the car cools down it retains pressure in the cooling system. I pull the pressure relief tab on the cap to relieve the pressure. It spits out enough water that I have to add some back before riding again. If I just let it set and not let the pressure off water eventually seeps out the front and back externally where the water jackets in the heads and intake join. I noticed this past week after I drove it on Saturday I let all the pressure out after it cooled down and put the pressure relief tab back down. When I went and cracked it again on Thursday after just setting all week it had built up pressure in it again....not a lot but some. I put gasket sealer around both sides of the gasket around the water ports when I put it together. While running, water doesn't seep out. There has been no indication at all of water in the oil either. I did the test of combustion gases in the cooling system and it tested that it was combustion in the cooling system. I can't figure out for the life of me where it could be coming from because the motor runs great with no issues. Does not loose water except for what it pukes out when the relief tab is pulled on the cap

The motor is a small block Chevrolet
Dart Iron eagle Block decked
Cometic head gaskets # CGT-C5249-070 MLS (It has 12.5 compression)
ARP Head Studs #234-4336
Dart 9* Ultra Pro heads new when put on the motor
Meziere electric water pump 42 gph
Radiator is a Be Cool factor replacement with a 16 lb cap


Any ideas would be appreciated.

[fabr]

Combustion gas in coolant test shows you have a combustion leak. Since it is building pressure I vote for a leaky head gasket. Next would be a cracked cylinder. Could be a cracked head. About all there is.

[Tom68]

Seems like combustion pressure in cooling system.

Is it a wet recovery system or are you running expansion space in the radiator ?

Cap pressure and recovery valve operating and to spec' ?

[fabr]

Seems like combustion pressure in cooling system.
Is it a wet recovery system or are you running expansion space in the radiator ?

Cap pressure and recovery valve operating and to spec' ?

It tested positive for combustion gas in coolant so ,of course, it is combustion pressure pressurizing his coolant and not anything to do with his cooling system. Therefore the cap and type of cooling system has nothing to do with his issue.

[David Redszus]

In addition to measuring and logging coolant temperature, we often track coolant pressure.

Frequently, the coolant pressure exceeds cap limits. Much depends on where the pressure is measured.
Often the cause is local flow blockage, especially when multiple radiators are being used.

Gas in the cooling system can originate from local coolant boiling. At some point the gas
pressure can lift the head and allow the addidtion of combustion gases.

[fabr]

Care to expand on the last paragraph? I'm having a hard time seeing that happen.

[David Redszus]

Care to expand on the last paragraph? I'm having a hard time seeing that happen.

Gas in the cooling system is steam resulting from coolant boiling.
Even though the system is pressurized, which raises the coolant boiling point, at some temperature
it will boil, expanding the volume massively.

I should have made the distiction between combustion gas and steam gas.

[fabr]

Thank you ,I understand that and did not think otherwise. What I cannot see is gas/steam/whatever in the cooling system building enough pressure to raise a head causing a combustion gas leak to the coolant. If the cooling system had no rubber hoses and was able to totally contain the steam pressure from a localized steam pocket I ,of course,see what you describe being able to happen . I mean something has to give but I just am very skeptical of an automotive cooling system being robust enough to contain the pressure causing a head to lift. Too many other places that will yield first namely hoses/radiator/heater core. I am not meaning to be argumentative since you are much more knowledgeable than me. I only seek to understand.

[fabr]

Perhaps I'm just being impatient,my apologies if so, but I would truly appreciate an explanation.

[Tom68]

Seems like combustion pressure in cooling system.
Is it a wet recovery system or are you running expansion space in the radiator ?

Cap pressure and recovery valve operating and to spec' ?

It tested positive for combustion gas in coolant so ,of course, it is combustion pressure pressurizing his coolant and not anything to do with his cooling system. Therefore the cap and type of cooling system has nothing to do with his issue.

Yer misread that bit.

Fortunately for me my last couple of suspected head gaskets have been cap issues.

[fabr]

The op plainly stated he tested for combustion gas in the coolant and it tested positive. I didn't miss a thing unless you can point it out for me.

[Tom68]

The op plainly stated he tested for combustion gas in the coolant and it tested positive. I didn't miss a thing unless you can point it out for me.

I missread that bit.

[fabr]

Thank you ,I understand that and did not think otherwise. What I cannot see is gas/steam/whatever in the cooling system building enough pressure to raise a head causing a combustion gas leak to the coolant. If the cooling system had no rubber hoses and was able to totally contain the steam pressure from a localized steam pocket I ,of course,see what you describe being able to happen . I mean something has to give but I just am very skeptical of an automotive cooling system being robust enough to contain the pressure causing a head to lift. Too many other places that will yield first namely hoses/radiator/heater core. I am not meaning to be argumentative since you are much more knowledgeable than me. I only seek to understand.

As I said earlier I apologize if I'm being impatient but I'm really interested in the above. If David Redszus could possibly help me understand .

[V12MECH]

Pull plugs, inspect for possible color variation, keep in order, grab compression tester., pull out Schrader, and rig it up to apply shop air into each cylinder at tdc. Leave radiator cap off, watch for bubbles and/ or coolant level to raise, wait a bit, 2-5 minutes, maybe longer, try it with engine cold or warm, that 120 -150 psi will usually show up a sealing failure. A crack down in bore ? We blank off rad and hose conns. Use air connection screwed into plate at thermostat opening and inspect each cylinder with boroscope at bdc, with water in block.

[V12MECH]

Another point, I used to use a 4 gas meter to check for CO at radiator cap opening and NAPA blue fluid rig on radiator to check for combustion gas, not sure what you are doing, It takes time, but the shop air test has yet to fail , and the napa Blue fluid has a shelf life of 2 years. Let us know what you find out.