Or just playing around. My car does the same (never put a clear tube though, but I have a permanent pressure gauge). I never worried about it because I feel like that's fairly normal, and the pressure returns when the pump primes. It could be either or, leaking back through the check valve or leaking past the regulator/damper. I doubt if both systems are still (or ever) 100% sealed.
------------------------------------------------------------------ 1992 300ZX NA 5 Sp (Dead) 1990 300ZX NA Auto 2+2 (Dead) 1990 300ZX TT 5 Sp (Est. 400 HP) 1990 300ZX TT 5 Sp (Est. 600 HP) 2004 G35 Sport 6MT (DD) |