Coolant pressure?

I was looking at my radiator today and noticed a little coolant leaking at the petcock. I opened the hood and went to loosen the radiator cap and heard it start to hiss like it had pressure from just being driven. The truck hasn't been started in a couple weeks. Is it normal for the coolant system to still have pressure this long?

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What you see on the bracket and belt is all it burped out

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Yes. Mine definitely does that. I was paranoid and put an exhaust gas probe on it at the local garage (sniff the "gas" coming out when you open the cap; if it is exhaust gas there is a head gasket leak). Nada. Just coolant pressure. Mine also has not read the TM and dislikes coolant being filled to the filler neck. Whenever I do, she will burp out a quart or so. That's where she likes her coolant to be. Never argue with a lady.

Thanks cattlerepairman, I was concerned but I'll give it the sniff test just to be sure.

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Mine also did that ,I found that the Copper overflow line was clogged, clean it out and never had pressure again after sitting , it doesn’t make sense I know but give it a look and see if it’s clogged

Big Tom

That's a good sign that the hoses and everything related to the cooling system is healthy and holding tight. You're truck doesn't have an overflow bottle and the cap holds around 7 to 14 psi of air pressure before it allows any overflow out of the radiator. If you fill a deuce radiator to the bottom gasket of the cap it will purge some coolant as it heats up and expands as cattlerepairman pointed out.

Thanks everyone for your input. I drove it today after adjusting the mirrors I installed awhile back. When I get home tomorrow I will smell check the radiator. Thanks again.

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Pressure in a sealed system should always return to atmospheric when temperature reaches ambient. System has no pressure when you put the cap on, so unless volume ( either fluid or gas, i.e. combustion gas) enters the sealed system then it should return to the same pressure ( atmosphere) when it cools. The headgaskets on these engines suck. Some combustion leakage is common, even if it is slight.

Mud wasps in the vent tube.

Big Tom said:

Mine also did that ,I found that the Copper overflow line was clogged, clean it out and never had pressure again after sitting , it doesn’t make sense I know but give it a look and see if it’s clogged

Big Tom

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Hi

Big Tom

May have hit this one DEAD ON THE HEAD, check the vent tube, I've had mud wasps plug the vent on non-pressure systems to the point it blew a 2 inch top hose off. With a cab forward that fills the cab with steam, collateral everywhere.

Now my service list is running a wire up the vent tube.

Cheers Phil