is it bad that after driving my stang I can go out a week later and open the radiator cap and its still under pressure? I've nver seen anything do this before.

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maybe theres air in there??

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no, I wonder if it has to do with the big ass aluminum radiator, I never had that problem with the stock 302 and that rad but uit also had a seaping headgasket on #5 cylinder so maybe the neck is made wrong and the spring on the cap is completely compressed when I put it on?

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Something about this is freaky. Your cooling system should never be under pressure when it's cold. The only reason it ever gets pressurized is when it gets up to temperature. Even then it's just pressure created by the law "as temperature increases pressure increases". That's why if you take the cap of when it's hot (not a good idea) it will release a sudden "burst" of pressure and then....... it's not pressurized anymore In other words there is nothing in the system that really builds pressure up. The water pump moves the coolant around but the system flows in a loop so there is no build up.

Maybe something is clogged somewhere. That may cause a slight build up of pressure. But, again the water pump isn't strong enough to truly "pressurize" the cooling system. Plus you would blow seals.



....wanna blow him??

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did you last open it at sea level, and are now on top of the rocky's?

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"Racing is a matter of spirit not strength."

no, maybe its a pressure difference, like a vacuum. All I know is you hear a big rush of air when you take the cap off, even when the car has been sitting for days

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is it rushing in or out?

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"Racing is a matter of spirit not strength."

IDK, I you can hear the movement of air, I can't tell if it is going in or out

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hmmm, you might have something going on where under pressure it either lets air out our fluid, and when it cools you end up with a vacuum. who knows as long as you're not noticing any problems with overheating just keep your fingers crossed lol.

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"Racing is a matter of spirit not strength."

You'll definitely want to determine if the air is rushing in or out when you pop the cap.
The coolant system is a sealed system but that doesn't mean it maintains 0 net pressure when cold. It could be at a vacuum when cold or under positive pressure. The altitude example is very real.

So if air is rushing in when you pop the cap, and then weeks later after running the motor and water pump it still rushes in that means you are generating vacuum which would indicate a loss of coolant...but the interesting thing is that a leak would serve as an inlet for air to satisfy the vacuum ... but that's not happening because the vacuum is sustained. Odd.

If air is rushing out then that doesn't make sense either because coolant systems have check valve overflow catches to relieve excessive pressure, and then the system goes back to stable when cool.

Geez dude I'm sorry...I just kind of though this out and I realized I don't have an answer for you. See which way the air goes and we'll take it from there.

One more afterthought - is your mixture 50/50? If it's too diluted the water could be boiling when the motor's running and converting to a gas, which could mess with your pressure...

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My thoughts are this, the radiator is aftermarket, maybe the filler neck where the cap seats wasn't machined right and when the cap goes on it is comressing the spring all of the way down to where the cap cannot relieve pressure for over flow. I don't have an over flow tank, just a line running down under the car, but I don't hardly get any coolant out of this line even if I fill the radiator to the top then run the car to about 200 degress. I might get about 10 little drops. With the old engine and same radiator it would leave a good sized puddle when I ran it after topping it off, that is the only reason I don't get how the above could be the problem. But on the old engine the head gasket on the left bank seeped enough to where I would get a very faint white smoke at all times. IDK its a wierd problem but it doesn't use any coolant and has yet to get above 205 degres. I guess I just won't worry about it, I was just hoping that someone had this happen to them before.

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if you are boiling your coolant you would know it. the weak point in your cooling system would let go. in my nissan it was the over flow tank lid getting blown off, but it could be the radiator, a hose, or the water pump. i doubt it's boiling.

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"Racing is a matter of spirit not strength."

I would normally doubt it (and hope it's not the case) too, but water boils at 212 degrees Farenheit at sea level (1 atmosphere of pressure). If his system is maintaining negative pressure and his mixture is diluted (primarily water) that could be happening even sooner....he mentions running at up to 200 degrees.
Just a possibility...or that aftermarket system may be too strong for its own good, holding in the pressure. I imagine there's a check valve at the end of that overflow tube. You might want to inspect that and replace if you can to make sure it's releasing at the intended pressure. They can gunk up and fail to relieve pressure.

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its not cloged, and I know it is building pressure or it would boil over.

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