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