pressure testing radiator

I was wondering how much of a pressure drop over what time would be considered acceptable before investigating, especially with respect to intake manifold seals?

I connected a tester and saw maybe a tenth psi drop over 10 minutes on my Lesabre. My dad's Tahoe has 1 psi drop over 10 minutes.

Assuming no leaks around hoses and/or the press. tester itself where it fits into the radiator, that may be too high, big question are you loosing coolant?

I'll try to double check the pressure sometime today. I suppose I could make a soap solution to put on and around the pressure tester attachments, although it would be tough to check where the adapter connects to the radiator. I when I tested it yesterday I only had enough time to leave it on for 10 minutes. I'll see if I can leave it on for a couple of hours today.

As for losing coolant, I'm not sure. At first I seemed to be losing some, but the car was new and if there was a little air in the top of the radiator due to some service that was done, it may have been purged out while I was driving. I did check the bleed screw after and got just a trickle of coolant.

So basically you're saying that any measurable loss, even a fraction of a psi, in a couple of hours would be too much?

Theoretically the cooling system is sealed, but if you test it warm/hot as it cools the pressure would normally drop, I have found that it will not seal 100% with a press. test, the key here is any measurable loss of coolant indicates a problem.

OK, assuming I have a measurable loss, say 1/10 psi in 10 minutes, how soon should I be replacing the intake manifold gaskets? Is there a good chance I could wait until next summer? I would monitor it every month or so anyway.

I've attached it to my Mercury which hasn't lost coolant since the last change this spring and will monitor it to see how much leakage I get from the tool and adapter.

One further question: My 99 has gray LIM gaskets. I assume they are not the aluminum gaskets supplied by GM. However, I thought that GM OEM LIM gaskets were black.

Unless this was replaced recently the 99 gaskets are not the updated type. Again coolant loss is the key issue here.

Were the original gaskets black beside the heads? I'm trying to figure out if they were replaced with an aftermarket gasket or if they are original gaskets.