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We see water pump failures all the time. We replace them EVERY timing belt change. Same for all the idlers, tensioner, and the thermostat (OEM or Tama only). Gates is Chinese garbage. Same for Fail-Pro - US garbage. They don't know Japanese engines. Junk. OEM 770 or 642 gaskets from the turbo engine. Aisin for the water pump. NTN, Koyo, and NSK for the components. Re-use the bolts. Clean them with mineral spirits. DO NOT wire wheel them. We NEVER replace bolts. Not a failure point. GD

You’re doing it way too slowly and quietly if you’re hearing a fraction of a teaspoon of air escaping! Lol

Not a big question, ain't no thang. Just kinda cool. While splitting this EJ25 block, with each of the block bolts I removed there was a little hiss. Didn't take long to figure out that wherever it was assembled - probably the factory - must have been rather lower altitude than my roughly 4000 ft. The US and Japanese plants are both in the 700 ft neighborhood.

Nah, the vapour pressure wouldn't be high enough. This is mos def trapped air. The threads get oil, but the sealant is on the block mating surfaces surrounding the bolt holes, so it's inevitable that some squishes into the bolt holes.

If threads were air tight it seems some would get notably hard to tighten in the process of tightening...I’m thinking this isn’t what’s happening. There are engine assembly bolts (not Subaru) that require sealant when they pass through certain areas as well - because the threads aren’t sealed. In theory threads aren’t engaged fully - one load bearing face of the bolt thread is seated against the facing load bearing edge of the receiving threads. It is not 3 dimensionally tight between the valleys and peaks. This presumably leaves a permanent spiraling air gap all the way up the shaft. Not sure what then happens at the bolt head surface but given most metal to metal areas get orings or gaskets I’m assuming it’s not air tight. Thats “theory” - in practice, an infinite number of interacting variables, some variation of possibilities would present themselves. So if you’re hearing this, no matter the cause, I guess it is right in the beginning when the head leaves the surface, the “potentially” sealed part and before the volume of the bolt hood shaft increases during removal.

Sheesh - kids.

slacker