A friend of mine has started having an issue of the coolant system still having pressure the day after racing. Dragster 582 BBC. No water in overflow. Titan Head Gaskets.

Is it just air that comes out or do you get coolant/water also?

Water came out as well.

The only way I can see that happening is with a leaky head gasket. I would remove rad cap and put air down each cylinder to try finding a leak.

Yep. We pulled the head off It was leaking on the edge of #1 cylinder.

Still doesn't make sense why its not putting water in the over flow. Cap might need replacing. I had a gasket issue, it would push water out and next week I would take the cap off and just get air pressure release. Drain the over flow and pour it back in and go race for the day.

It is likley a chemical reaction in the coolant system. Have him completely drain the system and flush. Is he using anything other then water in his coolant system?

My buddies SBC builds does this too. Take the cap off and make a mess. Re-install the cap and let it sit overnight. Take the cap off the next day and make another mess. It just builds pressure on it's own.

We put a radiator pressure tester on it and it made close to 3 lbs overnight.

He uses straight H2O and some kind of water wetter product to lubricate the pump.

I have found customers have best luck with Redline Water Wetter with distilled water or regular tap water.

Water Wetter instructions: "The anti-scaling ingredients in Red Line WaterWetter® allow its use with ordinary tap water. However, using withdistilled or deionized water will accomplish some scale removal in the cylinder head area."

Another thing often over looked is grounding the radiator. If your radiator is on rubber isolators you should run a chassis ground strap to it.

Changes in barometric pressure or altitude from when the cap is closed and when it's opened? ;^)

Check your coolant voltage. Positive probe of your DVOM in the coolant, negative on the chassis ground. If you have more than about 0.8v, first change the coolant and see if that helps (it does wear out) and if not, ground the radiator. If it's under 0.4v, you're in good shape.

That's the way the OEM has told us to do it at work, on tractors. Some guys order aftermarket radiators and they sometimes mount differently, and occasionally will need a chassis ground strap of some sort.