[stucky2947]

Got one for you. After I run my car for a while, doesn't get to operating temp, and let it sit (last time it was a few days), when I open the radiator cap, there is a lot of pressure released. What's up?

[STVSHOBRD]

My car does that all the time. I can remove the cap after sitting for two or three weeks and still get the release of pressure. I take it as a good cooling system-no leaks.

[GStage1]

Run your car w/o the cap on....if you see air bubbles....you have a bad head gasket(s)

[STVSHOBRD]

If the head gasket was leaking why would you still have pressure? Wouldn't the leak cause you to lose pressure?

[steve25]

A system good system will never have pressure in it once it has cooled all the way down, what you heard after thaecar sat for a while was air entering the rad when you opened the cap due to the vacume.

[GStage1]

The reason for the head gasket statement....I have found several engines with the same problem.....removed about 1" of fluid below the radiator filler hole, ran the engine without the cap on and watched as bubbles percolated in the fluid....the engine was pumping air/fuel mixture into the coolant......engines never consumed fluid.....due to the way the head gasket was letting the air enter the coolant. Replaced both head gaskets and no more air bubbles or pressure.

On a normal engine, you should leave a little room for thermal fluid expansion so you don't spill fluid. Once the engine/coolant returns to normal outdoor temperature...there should not be any pressure since the heat is gone.

[STVSHOBRD]

I would think that if thats the case when you shut the motor off and there is pressure in the system, coolant would leak through the bad area in the gasket and after time there would be no pressure left. Sometimes my car will sit for a month without running. I would think if there is a way for air to enter the coolant, there would be a way for coolant to go the other way.

[rotdog]

Mine does the same thing, Is it running hot? 200-220

[66Mutt]

Do you have a coolant recovery tank?

I wonder if the vacuum relief portion of the radiator cap is not functioning or operates at a much lower level of vacuum
I'm a waitin' to hear the final answer.
Doug

[GStage1]

220 is way too hot....only should happen during hot July/Aug days w/AC on and stuck in traffic.

Otherwise, you need to check your thermostatic clutch and rad.

[rotdog]

I don't have recovery tank but gonna get one and a trans cooler. Where is the pressure susposed to go when engine cools off? Mine like stuckys seems to stay pressured up.

[66Mutt]

With no coolant recovery, the coolant heats up and expands and pushes some coolant out of the overflow line. When it cools down, it contracts and air is drawn back through the radiator cap. That is why you often see the fluid level an inch or so below the neck of the radiator. The radiator cap is actually a 2 way valve. With the recovery can, coolant is siphoned back into the radiator to keep it full. Air helps break down the coolan and the corrosion inhibitors. I believe recovery tanks are a big reason new car radiators seem to last much longer without scaling up.

But the odd thing with it keeping pressure is that the cooling system starts out at 0 psig when it is filled. So as it expands and contracts it should return back to 0 psig.
I suppose if the system is filled with cold water during the cold months, it will have pressure on it once the ambient temps heat up.
I can't think of a reason to have any pressure on the system on a car that has sat for days. Typically I will hear it pull in some more air as I remove the cap.
Doug

[STVSHOBRD]

Maybe it is pulling air in, its kind of hard to tell. All I know is there is some kind of air release sound when you remove the cap.

[stucky2947]

I'm going to take it on another trip around the block this weekend. After it sits for a while (a day), I'll pop the cap with a lit lighter next to it and see which way the flame goes.

[huddie]

stucky2947,I know this is an old post but what did you figure out on the pressure deal?Mine does the same.I dont have a cooling problem but installed a recovery tank and it wont recover coolant.Has pressure after days of sitting.

[Formulabruce]

Got an air pocket? maybe bleed it?

[stucky2947]

I didn't find an answer to the problem, however, I did have a cooling issue. Mine ran 210 - 230 all the time. My stock radiator was only about an inch thick at the core. I bought a Griffin aluminum radiator which has a 3" core thickness and I don't have the problem anymore. Sorry I couldn't be more help.

[huddie]

Got it fixed today,It was an air pocket.Thanks

[Pontirag]

stucky 2947

Its not a problem. the fact that your system maintains a vacuum indicates that its good.

[80shaker]

So if my temp gauge is reading between 220-240 in traffic, but there's no pressure build up (nothing in the recovery tank, ever) would it most likely be a faulty sensor in my manifold? I've heard if they're too short it'll overreact due to steam. I'm running a champion 3-row and dual puller e-fans. Great thread!