Napoleon1991

I replaced my leaky radiator cap last week becasue every week or so the coolant would be down 3-4 inches in the radiator. This week after driving it for a while I noticed that my upper radiator hose was very squishy and I could take the radiator cap off hot without steam comeing out. The engine runs cooler now that ive replaced the cap and the coolant doesnt disappear but it seems that I still should be able to feel pressure. My old cap had let the engine slightly overheat but the hoses were still firm and steam would come out if I took it off hot. Im just wondering if I should be concerned by the lack of pressure, even though so far everything is running ok.

MDchanic

1. Although the cap IS a part of the cooling system, and does help cool the engine by maintaining about 15psi of pressure in the system when it's hot, it will not "let the engine overheat" under normal circumstances.

2. The cap is designed to allow the cooling system pressure to reach a certain point, then go no higher.
IF the cooling system has no leaks, the only way for pressure to get out is through the cap.
Since the system held pressure before you changed the cap, and does not hold pressure after you changed the cap, then it stands to reason that the cap is not working, but it does not PROVE that that is the case.
Now would be a good time to pressure test the system and the cap, and see where you are losing pressure.

- Eric

Napoleon1991

At first i assumed it was just a defective cap so i tried another used cap i had lying around and it still didnt hold pressure. Mayb i just have two bad caps? Unfortunately i threw out the original cap so i cant test it again.

oldcutlass

I agree with Eric on your new cap not working properly. Also you say that your coolant level was dropping 2-3 inches when it warms. I'm also assuming this is on your 69, which probably does not have an overflow tank, so the coolant goes on the ground. Normal level in a closed system is around 2 inches below the neck.

Did you ever figure out where your oil was going?

Napoleon1991

Thanks. I will try a new cap asap. By the way someone added an overflow tank so that wasnt the reason i was losing coolant.

oldcutlass

So then your coolant should be going into your tank when hot, and back into the radiator when cold. You need a cap for a coolant tank, usually 6-12#'s.

Did you ever solve your oil consumption issue?

Napoleon1991

Thanks. Hasnt had an oil consumption issues since i started that thread so il keep my fingers crossed. I still have no idea what happened to that quart of oil.

Napoleon1991

For anyone whos interested, the cooling system pressure issue i had went away when i filled up the overflow tank. Not sure why having the overflow tank low would cause a loss of pressure in the radiator though.

oldcutlass

Or maybe your cap wasn't seated the first time. Glad it's working.

Lady72nRob71

Make sure there was not debris or a dent or depression on the radiator tank neck that would prevent the cap from sealing. I once had a neck with a blob of solder on the seal surface!