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Passing leak down test with blown head gasket?


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Hi all. I know, I know, the search feature. 

Anyways, I rebuild the top end on my banshee and it went smooth, no issue going together. Everything was properly torqued, proper heat cycles, new gaskets, copper spray sealant on the headgasket. Passed the leak down test loosing zero pressure in 6 minutes. Compression checked out at 120 on both sides (stock head not cut) 

Mods: 

20 over with wiescos

billet intake

stock pipes with DG silencers

pro flow intake w/ k&n style air filter 

27.5 pilots

280 mains

+4 timing

93 octane fuel

50:1 ams oil dominator (36:1 for initial Break-in) 

So the problem I’m having is I finally got a  got to take it for an actual ride to the sand dunes instead of just around the block. Once it was finally warmed up and I started spanking it a little bit, it immediately started dumping coolant out onto the pipes, I’m thinking fuck the water pump went out again (stupid plastic gear)  I got it home and went to replace the water pump but it was not broken or damaged, huh. Checked the oversize radiator that was not clogged, leaking or plugged. Welp must Be a head gasket then right? So I pulled the motor, drained all the fluids and did ANOTHER leakdown test on the motor (6psi in 6 minutes) and it did not drop a single cunt hair.  For the hell of it I used a flashlight and looked in the cylinders, the stater Side cylinder seem to have noticeably more wear on the cross hatching (thinking maybe coolant was washing out the premix) So I pulled the head. 

Piston wash looks pretty much identical 

plugs look identical (little rich)

my question is, can I have a bad head gasket and still pass the leak down test? 

How come it doesn’t leak when the motors not up to temp yet? Would the heat warp the head until it cools off then seals back up? 

One thing I heard and read was that the coolant system operating pressure is much higher than 6psi, maybe that’s why 6psi won’t show anything? Sorry for the long ass write up, just trying to get this figured out so I can have something to fuckin ride. Someone’s gonna have some shit to talk to, I get it. 

 

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Do you have the overflow bottle? Or is the overflow tube just routed near your pipes?

I'm betting it just burped some coolant out. It'll stop once to coolant level adjust itself.
If you had a coolant leak into the cylinders, you wouldn't have any piston wash. The steam cleans the cylinders and pistons pretty good.

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running a overflow bottle still, kind of thought that my self but it happened a few times thinking maybe since it was a warm day and sand has such a drag affect but it also got topped off. Another thing I thought about was that I was running regular green 50/50 mixed coolant instead of engine ice or something more “quality” I get these high reving motors get hot in the sand sometimes but it should not have been this extreme, that’s why I thought I knew it was a water pump right away.  

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