Cooling system pressure
 

I'm having an issue I have never heard of or had experience with.My cooling system [SBF]is maintaining a high pressure even after long periods of shut down[weeks]! I noticed external weeping of coolant at the bottom of the heads and at the ends of the intake manifold.I checked the expansion tank,it was empty!I went to open the radiator cap so I could drain the system,it had enough pressure to blow the cap up as I turned it,it hit the stops then puked fluid!I pulled the intake and heads[aluminum],no signs of blown gaskets! Any ideas? I'm lost on this one! ROY.

Re: Cooling system pressure
 

Roy,

The system is designed to run "under pressure", so the first place I'd look would be at the cap to make sure it was relieving that pressure, above the PSI rating on the cap into the overflow container. If you can get a hold of a cooling system tester - Stant used to make a good one, but so does Mac, Snap-on and Cornwell, it will make the diagnostic's easier.

I run a 7 PSI cap on my 'wagon, which gives me just enough pressure to ensure proper cooling.

Good Luck!

Lew

Re: Cooling system pressure
 

Autozone rents presure testers around here. They charge your CCard then refund the charge when you return it. The tester has a couple of adapters so you can test the cap - thats where I'd look first.

Re: Cooling system pressure
 

I have run into this problem in the past.. What I found most of the time I had an air pocket somewhere in the cooling system.

Re: Cooling system pressure
 

the cap is obviously good, or it would not hold pressure that long. there would not be any leaks in the cooling system or it would not hold pressure that long. most likely an air pocket in the system somewhere. you may have to raise the front of the car way up to get it to 'burp'. after the season is over, pull the 'stat and drill at least one 'air bleed' hole in the 'stat housing.

rod in AZ

Re: Cooling system pressure
 

Thank You everyone that gave suggestions.I do not run a T-stat,so no restriction there.The air pocket makes sense,even though I fill the system slowly and with the upper hose off at the radiator and turned so as to be the highest point in the system.I spoke with two engine builders today,they both said it had to be blown head gaskets even though the gaskets do not show any damage!! ROY.

Re: Cooling system pressure
 

I would pressure check the cap. May not be releasing at the proper pressure. Five to seven psi would be plenty. I actually don't run any pressure in mine. I just cut a small "V" in the rubber gasket. Never a problem. I jack the front of my car up when I fill the cooling system, and run my electric water pump while topping it off.

Re: Cooling system pressure
 

the only time I have evetr seen this on a SBF is when someone installed the head gaskets backwards.

Re: Cooling system pressure
 

I was going to suggest a "no pressure system". I have always used a cap that seals at the top but no pressure mechanism. There are advantages.

Re: Cooling system pressure
 

x2

Wade

Re: Cooling system pressure
 

I use Evans NPG coolant with a zero pressure cap.
my spare engine is an old Comp engine that has some heads that leak a little, not unlike some SS heads.
This stuff works great and is race legal as it is not an ethelyne glycole base and cleans righ up.
It boils at 360 deg F at no pressure and has a very low expansion rate.
not cheap, but it works great and can be reused for several racing seasons.






http://www.evanscooling.com/products/coolants/npg-2/

Re: Cooling system pressure
 

What is the advantage to running with no pressure?


On the Evans coolant do you have to run thier pump with it? At one time I thought you did.

Re: Cooling system pressure
 

the big advantage of no ,or low pressure ,is no pressure to force coolant into ports ot combustion chambers.
I run the Evans with a Mezire pump with no problems.
Evans has several coolants and they also offer thermostats ,pressure caps and hi flow water pumps,but I dont recall a specific requirement for using their pump.