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This boost leak test has me stumped

Kapok6

Proven Member
1,393
258
Aug 10, 2004
Fort Worth, Texas
Alright, I have been trying forever to figure this boost leak out and have been unsuccessful thus far. Here are the facts.

Boost leak test reveals boost leaks coming from the dipstick and the valve cover. (see vid)

Dsm boost leak test - YouTube

Initial thought...boost leaking through rings pressurizing the crank case and thus casing the head to be pressurized as well as that pressure would also come up through the oil ports into the VC area.

I did a compression test (built motor) and it's 160-170 across. That's not adding oil into the cylinders, that's just pulling the spark plugs and testing.

2nd theory, my valve seals have to be leaking then, allowing pressure to go from the head/VC area through the oil ports into the crank case therefore pressurizing the whole system. So I pull the VC to see if the seals are leaking.

2nd vid
Dsm boost leak test 2 - YouTube

I can not detect any of the seals leaking. But pressure is still coming up from crank! If the seals were leaking, with the VC off, the crank case shouldn't see any pressure. The pressure would come through the valve seals and into the atmosphere since there is no VC to hold the pressure in.

You can also hear what sounds like oil bubbling through oil. So now we are back to, " the leak has to be originating though the crankcase first then into the head. Bad turbo seals allowing oil into the oil feed/return? I have had these results with 3 different turbos! Rebuilt MHI Evo 3, and two FP 3065's.

I am stumped. I have no idea where this leak is originating!

Any other thoughts?

-Ryan
 

brownfinger

Proven Member
1,961
10
Aug 26, 2008
Normal, Illinois
Isn't it pretty normal to have a little leakage around the rings on a static BLT? The rings are designed to seal when hot, in motion, for brief periods of the cycle. Not under constant pressure while cold and motionless. I always get a little leakage into the case, out the breather, dipstick, etc... You're checking for boost leaks in the intake track. They are very obvious, even with a little leak-down. I don't know about the bubbly oil, though.
 

turboglenn

Proven Member
6,379
104
Nov 5, 2007
RIpley, West_Virginia
There's always some leakage, You'd have to literally pull the cams to seal the intake tract off completely from the pistons, plug the PCV system and unhook and plug about every vacume line and accessory on the intake system in order to have no leakage somewhere in the system, what you're wanting to find are leaks to the atmosphere. Things like TB seals, leaking couplers, holes in FMIC core, etc..etc... those are the ones that hurt performance, (also, a PCV that isn't locking when boost is applied should be replaced as well, they are known to be junk on our cars. The good thing is there's ones ytou can find that are generic with the same thread and shape at O'reilly's that actaully will hold boost and open when the should and not need replaced every 2-3 weeks, i've been running the same one for a couple years now and it still doesn't leak (but watch, since i bragged on it, i'll find it blown apart tomorrow LOL )
 

ramsack

Proven Member
3,286
16
Dec 27, 2007
West Lawn, Pennsylvania
PCV valve. They're junk and leak boost. I've also had turbos let air past the oil seals.
 

Kapok6

Proven Member
1,393
258
Aug 10, 2004
Fort Worth, Texas
How about doing a leak down test?

Haven't done a leak down test yet.

The bubbling is air going past the turbo seals down the oil tube and into the oil pan.

That was my thought, but on 3 different turbos? A Used FP3065, New FP 3065, and a rebuilt MHI Evo 3? I find it hard to believe seals on 3 dif turbos are blown.

There's always some leakage, You'd have to literally pull the cams to seal the intake tract off completely from the pistons, plug the PCV system and unhook and plug about every vacume line and accessory on the intake system in order to have no leakage somewhere in the system, what you're wanting to find are leaks to the atmosphere. Things like TB seals, leaking couplers, holes in FMIC core, etc..etc... those are the ones that hurt performance, (also, a PCV that isn't locking when boost is applied should be replaced as well, they are known to be junk on our cars. The good thing is there's ones ytou can find that are generic with the same thread and shape at O'reilly's that actaully will hold boost and open when the should and not need replaced every 2-3 weeks, i've been running the same one for a couple years now and it still doesn't leak (but watch, since i bragged on it, i'll find it blown apart tomorrow LOL )

PCV valve. They're junk and leak boost. I've also had turbos let air past the oil seals.

I don't have a PVC valve. I have a crank case vent system nearly identical to Paul Volk's.
 

slayer450

Proven Member
466
3
Sep 1, 2011
pontotoc, Mississippi
That was my thought, but on 3 different turbos? A Used FP3065, New FP 3065, and a rebuilt MHI Evo 3? I find it hard to believe seals on 3 dif turbos are blown.

The seals aren't blown, they just leak with no oil pressure behind them. Heat the car up, take it around the block and do the test again.
 

[email protected]

Proven Member
223
32
Apr 20, 2012
McKinney, Texas
Do a leak down test.

Pressure leaking into the bearing housing through the gas control rings would not pressurize your crankcase to that extent.

- Michael
 

NightRider97

Proven Member
186
0
Jun 29, 2006
SW, Nebraska
I'm having this exact same issue with a FP3052 that has always had a restrictor on it. Leak down and compression tests on this engine are perfect. The air is definitely leaking into the crank case via the compressor side of the turbo. So I'd honestly like to know, why did this happen? This guy appears to be having the same issue.
 

NightRider97

Proven Member
186
0
Jun 29, 2006
SW, Nebraska
I did exactly that, tested at the throttle body and I have no blowby coming from the valve cover breather anymore. Test it from the turbo and all the boost leaks out of the valve cover breather. Here's what baffles me. There's no shaft play in the turbo and its always had a FP restrictor on it and I've always used the FP blue oil drain hose with it.
 

[email protected]

Proven Member
223
32
Apr 20, 2012
McKinney, Texas
Turbos have gas control rings these are dynamic seals just like your piston rings which means they have a tiny gap in them when installed. It's normal when not in operation that some pressure will bleed through the gas control rings and into bearing housing and through the oil drain. However we're talking about thousands of an inch gap, maybe enough to put 1psi or so into the crankcase.

-Michael
 
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