I dont see how the cylinder leakdown test can relate to pressurizing the coolant system issue. If your headgasket are leaking at cylinder pressures of only 100 psi, It should have pressurized the coolant system at idle as well.

I have always thought that normally a leakdown test was to show the sealant of the piston rings and valves. Leaking rings you will hear a fuzzing sound in the crankcase and leaking valves you will hear it in either exhaust and/or intake.

Thanks

 

I only just noticed that Liqquid stole and modified my headgasket picture! lol
here's another one i did

 

no when you do a leakdown test its pressurizing the cylinder and whatever gets by the rings is considered blowby and will enter the crankcase.

however, the headgasket clearly sees pressure as well since its in between the head and block.

this test i did just showed at this level of psi that torquing the headgasket more lowered the leakage at that specific PSI.. im well aware that i couldn't duplicate an actual combustion event with a compressor.. that takes thousands of PSI..

---

on another note, the reason i thought i was pushing coolant was because i blew 2 waterpumps in a row.. later after i did trouble shoot this issue and bought a water pressure gauge i found out what was causing it.. 50psi~ in 4th gear on a fp black.. doesn't work to well.. blow the water pump every time after 30-40 pulls.. and the reason it occurred was because the beta spring i was using in the hallman mbc was binding up + i had to much preload on the WGA. instantly in 4th gear the water pressure gauge would be maxed out everytime.

even after all that abuse the headgasket still never blew or got compromised.. so when i see people blowing headgaskets i always wonder to myself.. wow its so hard to blow a HG yet people manage to do it so easily.. the 3 main causes are faulty installation, bad machine work, tune.

I have cars i done on standard ARP's running 42psi+ and having no issues at all, so the way they are installed is certainly very important..

My car just takes a lot of tq for some reason.. quite possibly my torque wrench needs recalibrated. but mine are set at 130 right now.

but again.. ive yet to see a headgasket blow on one of my personal cars and i really beat the **** out of them.

 

My block and head are both o-ringed while using regular ARP studs but I'm not really pushing that much boost right now. I'm still using the stock turbo. I just bought L19's, a new head gasket, and I'm getting a larger turbo pretty soon so I'd like to see what boost of high 30's to low 40's can yield on a FF HTA86. Sounds like you may have a warped deck or head though. ~5% loss is nothing to lose sleep over regardless. I'd just keep track of it and look into it if it gets worse.