Coolant pressure while cold

[nek]

Im having overheating problems. While my engine is under load my temps shoot up to 240+. If I stop, turn of my engine (both fans on), and sit for about 20 seconds, when I turn on my engine the temps drop back down to 203.
Another thing I noticed, I have one of those pressure release tabs on my radiator cap. When the engine was cooled down after a hot run, I pulled the tab and I noticed my overflow filled up, like I could actually see the stream filling it up. Kind of like when you turn on a gardening hose face up underwater and it streams out the top. So it seems to me my coolant system is staying pressurized even when the system cools down.
Whats the deal? I know if I top off my coolant, it will push the coolant when it gets hot and obviously it wont fill my system back up when its cold because there is still pressure in the system. What do you guys think?

 

[jdpromm]

Your cooling system should not be under pressure when the engine is cold because when you fill the system you remove the rad cap which equalizes the cooling system pressure to ambient pressure. Are you absolutely sure your engine was totally cooled down? It sounds like a head gasket leak might be a possability. That would deffinitely cause overheating if combustion gasses were leaking into the water jacket and this could also account for having some system pressure once the engine is cool. A compression test might be in order. It would be good to do the test while the engine is warm because if the cooling system is holding pressure when it is cold then it might be somthing that shows up only once the engine is warmed up.

 

[nek]

Thats what I figured. Ill do a compression test as soon as possible.

 

[scott91370]

When you say it is pressurized when cooled down after a hot run, do you mean it is back to ambient temp? It takes a long time for the pressure to disappear from the system due to heat.

 

[nek]

When you say it is pressurized when cooled down after a hot run, do you mean it is back to ambient temp? It takes a long time for the pressure to disappear from the system due to heat.

Actually the more I research and more I think about it. The system is supposed to cool down and the rad cap uses the vacuum to open in the opposite direction and suck coolant back in. In a perfect system, all the coolant that was pushed out from heat enduced pressure, would come back into the system from vacuum.

In my case however, when the system cools down, no coolant is pulled back in due to pressure (not vacuum) being contained in the system. This is how pushing coolant works (I guess). If I continue to top off my coolant system, all the coolant would continuously be pushed into the overflow and never pulled back in and eventually just overflow out of the bottle all together. Im almost positive that its the headgasket causing my cylinders to pressurize the system but Im still gonna do a comp test when I get the chance.

Any other ways the system can get over pressurized other then headgasket failure?

 

[nek]

Wow, so I finished a compression test. High 180s across the board.
What the hell do I do now?

 

[TheWanderer]

Is your thermostat installed the right way (in the right direction)?

Are you leaking coolant anywhere?

I'd suggest replacing your thermostat with a new one (failsafe Stant is recommended), and draining the cooling system and refilling it after running the car for about 2 days with water and cleaner in the system. Make sure when you drain the cleaner/water mix out that you run a garden hose through it for at least 10-15 minutes, so it gets as much of the radiator cleaner out. Then top of with preferred mix of antifreeze/water, and see where things are from that point.

It sounds to me like you have a clogged system and/or a failing thermostat. Or your fans aren't pushing enough air.

 

[gpopppa]

I agree on the thermostat. And also replace that radiator cap,my experience hasnt been to well with them,Others may have good things to say about them, they work well to release pressure but still, Might be the cap and thermostat. And to get it backwards,..doubtful. Good luck man!

 

[nek]

I dont really know if its possible to install it backwards is it? I have the small end pointing towards the engine. Large portion is sitting with the rubber gasket. (It is a new tstat maybe Ill get another one?)
My fans do pull tons of air so I dont think thats the problem.
And I have bought 2 more rad caps trying to fix the problem so I dont think thats the problem either. Does a compression test tell you for sure its not the head gasket? I thought the only way to be 100 percent sure was to do a leak down test.
Ill go get another tstat and tell the guys mine is defective and see what that does.
When I pulled my plugs, 2&3 had some minor liquid on them compared to 1&4(outsides)

 

[kmj 4g63t]

A compression test will tell you if your HG is blown yes. A leak down is more thorough and it pinpoints were the leak is coming from (hg,intake exhaust valves,cracked head/block etc).

Pressurize your cooling system to 15-16psi and test the rad cap, you said you tried a couple and nothing changed but just to be safe test them! Test it and let us know what happens, x2 on the thermostat also. It is possible to install it backwards.

 

[vandenberg33]

Like kmj 4g63t said a leak down test is the best test to run but If you don't have a leak down tester.
Run the car till it warms up to operating temperature and the thermostat should be open.
While it is warming up their should not be much pressure in the radiator hoses if their is it has a blown head.
Shut the car off when it is warmed up and let it sit till it is completely cooled down and check for pressure in the hoses again.
Once again if their is pressure then you have a blown head gasket.
Usually a head gasket leak like this would be caused from warping of the head between cylinders 2 and 3 and pressure goes into the two cooling jacket ports between them, so if it is blown you will probably need the head resurfaced.

 

[Colt4G63 also]

Look down into your spark plug holes. If the tops of #2-3 pistons are clean, and # 1 and 4 are black, then it's leaking coolant into the cylinders.

 

[kmj 4g63t]

That isn't the only thing that will cause pressure. If you have air in the cooling system and you run the car, you take the rad cap off and you get a giant volcano of coolant everywere. I thought my car head a blown hg did a compression test and everything was fine, I bled the system kept taking the cap off seeing if there was pressure and stopped when it settled down.

Just do the test let us know simple as that....

 

[vandenberg33]

If he has pressure while the car is still warming up then It isn't air in the cooling system but an air pocket can cause symptoms of a blown head after it warms up. It just won't have near the pressure in the hoses as a blown head would have.

 

[nek]

Im almost possitive it isnt air in the system. I burped it pretty good.
I want to do a leakdown test because most my signs tell me its a headgasket except for the compression test.
I changed the tstat and blew a turbo coolant line when I was test driving it. Where can I get some of the rubber lines that have a natural 90 degree bend to them? Regular rubber lines would probably kink.