1G What is typical cooling system pressure?

[stryker]

I have been trying to track down a coolant leak or possible head gasket issue, and rented a cooling system pressure tester. The motor was rebuild under 1000 miles ago with a 4 layer metal HG, both block and head were machined, Manley pistons, Eagle rods, etc. I let the car warm up with the tester installed to watch for a jumpy needle or high pressure. The tester needle slowly builds all the way up to 21 psi as the car hits 200 degrees on link, and as the thermostat opens and fans kick on, the pressure drops back down to 16 psi. I watched the gauge as this repeated itself like clockwork 5 or so times. I search on typical cooling system pressure, and couldn't find anything. I know the stock cap is only 13 psi, so an operating range higher than the cap pressure didn't sound right to me. Anybody know what the typical range should be? Thanks.

 

[Colt4G63 also]

The normal pressure is 13psi, but when you removed the cap and installed the pressure tester, you disabled the pressure relief system. It's lucky you didn't blow part of the cooling system up.

Ps. Try hot torqueing the head studs.

 

[stryker]

Ok, I'll give that a shot. With the stock cap releasing at 13 psi, I didn't know if the typical range was well below that and the cap pressure release was only rarely used or if it hovered close to that pressure all the time.

 

[JusMX141]

The rad cap should act as a wastegate for your cooling system, keeping the system pressure at or below the spring pressure on the cap. If you're running a 13psi cap, then theoretically the cooling system should be at or below 13psi.

I'm guessing that since you had the pressure tester on in place of the rad cap, once the water reached the boiling point the pressure began to rise until the thermostat opened- allowing cool water to move through the system and hot water to flow into the rad. This circulation then lowered the pressure in the cooling system.

 

[jrohner]

To check for leaks, you pump in the pressure (not run the engine) and then watch the needle on the gauge and look (and listen) for leaks.

 

[jtmcinder]

The rad cap should act as a wastegate for your cooling system....

The one (and only) time that I've ever seen a situation where the term "blow-off valve" is actually the correct term to use for a DSM part and you go and call it a "wastegate." Bummer.

 

[JusMX141]

Ah yes, but in reality the blow off valve's function is to dump all pressure....the wastegate's function is to only vent as much pressure as needed to maintain a certain amount of pressure in the charge piping. Seemed to me that wastegate was more fitting.