Hot vs. cold compression test.

Did a hot compression test yesterday. All cylinders came up to 150psi, except one(stayed at 130 or so).

All the cylinders are around 125-130 cold...

What does this indicate, any ideas? Tight valve coming off the seat a bit when hot maybe?

The 20 - 25 psi shift on the ones that came up to 150 indicate ring wear, but might still be serviceable for a while (although marginal). The low one probably has a valve that is not seating well. Definitely want to check valve clearances first.

T, for your' consideration..better comp. #'s when warm indicate worn pistons & rings. as pistons come to temp they grow, causing them to travel straigher in bore, allowing for better ring seal even worn. same for rings. tight valves just the opposite, as valves heat, clearances decrease.and compression drops. if curious, a squirt of oil in plug holes and comp check will verify. your' low cyl could be as noted a tight/burnt valve. it could also be stuck/ broken ring/s. a leakdown test would show where comparitive losses are. random rambling, luck g