Pressure testing cooling system

[davepl]

I made some radiator repairs and I've pressurized the (otherwise empty) system with my Stant pressure tester.

I ran it up to 15psi and let it sit. It's losing about a pound every 5 minutes or so.

I assume this means I still have a leak somewhere? It can't be going nowhere. But I don't know how "tight" a cooling system is or even if the tester itself should hold pressure overnight, that sort of thing.

Anyone know what's "normal"?

Thanks,
Dave

[MARKDTN]

Make sure the gasket on the tester is in good shape and wet it before you clamp it down. That small could just be the tester, but sounds like there could still be a leak. Make sure your heater clamps are good. How about the heater core? Is it new? Those testers are a great tool. Really small leaks can drive you crazy.

[hamjet]

get out your tire soap and start spraying for leaks...

[davepl]

Wife didn't want me submerging it in our bathtub :-)

I did find a leak at the base of the thermostat housing with soapy water. Turns out the gasket I used had an adhesive back (peel and stick) that I didn't see (and hence didn't peel) and it was coming out of that. So I redid that and I'll recheck today. Thanks!

[davepl]

Well, I'm unable to find any more leaks after a couple of bottles of soap/water, but it won't hold pressure indefinitely.

I put 15psi in it around noon, which is 5 hours ago, and it's now at 11. So it's still losing about a pound an hour. Air might leak a lot more easily than coolant, that's my hope anyway.

So if I think it's losing air and I can't find any more traces at the hose connections and every point I can think of on the rad, then what? It could be in the heater core somehow (brand new) or out of the heater valve (brand new) and I'll not know about it until it's a problem.

[hamjet]

You might have to break it down some, ( remove the heater core from the test by running one of the heater hoses back to the other one). are you running the pressure through the whole engine, water pump ? I wonder if the water pump seal is sealing enough for just air...could the rad hoses be expanding over time which will make your pressure drop? ( just thinking out loud)..I don't know much on how your stant tester works, but is it possible air can be bleeding back through it? I don't know....