AirLift won't hold vacuum on drained system.

[NewArt]

Just to flollow up, I never found the leak but I suspect that the releif valve wasn't sealing properly, maybe because it had sat empty in my minus 10 garage for a couple of months. I managed to get the vacuum to -26 ( my bad: I hadn't turned the pressure up on my compressor ) although it wouldn't hold. I Got it filled after 3 tries. Today I ran it while up on jack stands until it got up to temp. There was about 3 drops of coolant that came out the overflow tube but no other apparent leaks. The tank is recent and it comes with the relief valve so I'm a bit surprised that it didn't seal properly. Has anyone else seen this problem?