Pressure in the radiator after 8 hours?

Question

I just went to check my oild in a 78 buick regal 3.8 v6 and I squezed the upper radiator hose and it seemed if their was pressure in it still after 8 hours so I popped off the cap and had plenty of pressure it started spilling out everywere what could couse this?

Answer 1

There should not be pressure remaining after the engine has cooled. There is a problem. Sounds like something is plugged up. Is it running hot (why did you decide to "CHECK" it?), if so replace t-stat and flush out cooling system. Watch what comes out (look for rust, hard scale particles etc), maybe even replace the radiator cap.

Answer 2

You need a new radiator cap. The only other possibility is a cracked head or block, but if you aren't having a boiling over problem, I doubt that is it. Try the new cap.
The pressure rating on a radiator cap is the maximum pressure of the cooling system. When that pressure is exceded by the heated coolant expanding, the coolant is bled into the coolant reservoir. Indeed an good cap will keep the system at that rated pressure. But once the engine cools the vacuum created inside the cooling system sucks the coolant from the reservoir to the radiator. Your cap is not letting that happen.

Answer 3

Too bad these halfwits don't know how to read a question. You just have a good, tight system. The ambient air temperature going up can be enough to warm the coolant and create some pressure in the system.

Answer 4

Properly working radiator cap valve relieve maintains 15 psi pressure. If I were you, I would worry if there was no pressure...