Cooling system pressure problem

[gramps]

358 sbc circle track motor, dry sump not vented, cooling system is building enough pressure to vent water pass the 29/32lb cap into over flow can, continues to do this causing a loss of water, motor is strong as it was on day one, 180/190* while on track, never over heated. Strange part, days after race day system is still under pressure. Any ideas?

[gramps]

Little more info, first three races no venting of water, no pressure next day after water cools down, really has me stumped.

[dieselgeek]

detonation lifting head perhaps? Pressurizing the coolant passages, at least in my experience, means you're getting combustion pressure in the cooling system.

I use CLT pressure gauge on turbo apps so I can see the onset of lifting a cylinder head. ON an N/A engine I'd think this has to mean detonation/preignition/whatever.

Just my $.02, hopefully someone smarter at circle track engines chimes in here soon.

[Keith Morganstein]

358 sbc circle track motor, dry sump not vented, cooling system is building enough pressure to vent water pass the 29/32lb cap into over flow can, continues to do this causing a loss of water, motor is strong as it was on day one, 180/190* while on track, never over heated. Strange part, days after race day system is still under pressure. Any ideas?

Strange one, but my thoughts are a combustion leak in a head gasket that is acting as a one way (check) valve.

I would get a combustion leak detector, available from Snap-on or other suppliers and test it.

[beaker60]

358 sbc circle track motor, dry sump not vented, cooling system is building enough pressure to vent water pass the 29/32lb cap into over flow can, continues to do this causing a loss of water, motor is strong as it was on day one, 180/190* while on track, never over heated. Strange part, days after race day system is still under pressure. Any ideas?

Strange one, but my thoughts are a combustion leak in a head gasket that is acting as a one way (check) valve.

I would get a combustion leak detector, available from Snap-on or other suppliers and test it.

X2 on Keith's diagnosis,,,those leak detectors are almost a must,,,and they don't leave any doubt.

[Pavillion]

Had one do that ten years ago on SBC 18 deg circle motor. #3 head camber had hairline crack with a mind of its own. Ran fine some nights, pushed water others. Finally found it with pressure testing as mentioned above.

[donc]

I have found radiator caps brand new that did not hold advertised pressure, especially if its an aftermarket radiator, seems the neck that cap goes on can vary in depth, too deep and it lowers value of cap. What Ive done in the past is pressureize the system with air through the drain plugs at bottom of block, using an accurate regulator,remove spark plugs, listen for air in cylinders , and rest of system.

[91vette]

Pull the plugs and rockers. Run full shop air in each cylinder assuming it is around 125-175 not that it should matter if more but needs to high enough to be useful. This might find it. The fact that it is under pressure days later even hours later after cooling down is curious. It would make me think there is no water in it and all air pressure. What it is beyond a 358 circle track engine might offer some clues.

[gramps]

Update,ran a compression leak check, nothing. Pulled the top end off motor just to be safe, finding nothing wrong (cracks or bad gaskets) looked at the coolant additive (Amsoil) we were running. Not sure if we had added distilled water at some point which is a no no when using this additive. Changed to a regular water wetter, been running fine since putting back together. Was really weird, you could vent the colling system and come back after sitting three days later and the system would be pressurized.

[Warp Speed]

Was really weird, you could vent the colling system and come back after sitting three days later and the system would be pressurized.

That is typical chemical reaction. You can get it from either improper coolant mixing (like you say you may have had) or just from minerals in the water reacting with an aluminum radiator.

The above statement, along with your inspection points toward that for sure.

[robert1]

I had a friend one time tell me he had a head gasket leaking because the engine would build so much pressure during the week it would push water out of the overflow. I tried explaining that it wasn't possible for the head gasket to leak and build pressure if the engine hadn't been run. Anyway I go over in the middle of the week to see what is going on. Sure enough it's pushing water out after he had opened the cap. When I checked the hose it was tight as could be. I cracked the radiator cap and this smelly water blows everywhere. I asked him what he had in the radiator and he said water wetter. I told him this isn't water wetter and he says it's just a different brand. He hands me the can and I see it is radiator etch. It was a cleaner that was causing a chemical reaction.

[dwilliams]

I use CLT pressure gauge on turbo apps so I can see the onset of lifting a cylinder head.

I recommend them for road race or track day motors. In case of sudden loss of coolant the pressure gauge responds much faster than the temp gauge. Depending on where the coolant temp sensor is, loss of coolant may actually cause the temp gauge to read cooler; cars with the sensor in the radiator, for example.

Actually, I just use the cheap 5 PSI GM oil pressure switches and an idiot light; a gauge isn't necessary for that application.