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Excessive blow by with good compression?

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Adam7917
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Excessive blow by with good compression?

Post by Adam7917 » Tue Aug 13, 2019 11:29 pm

Hello all, I have an ‘87 244 with over 200k miles on it that I did a +t to. The issue I’m having is that excessive pressure is causing it to leak quite a bit and the oil won’t drain from the turbo fast enough. The Pcv breather was routed to the intake before the turbo, and I installed a vented oil cap to try and band-aid the issue to see if it would help at all. What ends up happening is that under boost it sprays oil out from the cap, gasket, valve cover gasket, and leaks over onto the exhaust manifold to burn off. Compression is around 150 psi on all cylinders. The oil burning gets very bad on the highway when it’s in boost at 10psi most of the time, and creates a smokescreen. If I turn the boost down to 3-4 psi it doesn’t seem to smoke... I’m looking at rebuilding the engine but don’t want to if I can avoid it.



jimmy57
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Re: Excessive blow by with good compression?

Post by jimmy57 » Wed Aug 14, 2019 9:59 am

When the rings fail and lose effectiveness you can get combustion deposits that raise compression test pressure and the oiling of rings also improves the sealing. Both of these have no effect on the rings actually leaking compression and increasing crankcase gas volume. Compression test is only one piece of the diagnostic puzzle.

1987 240 turbo? what engine has been installed in that car? is it the 240 B21FT or a B23FT or B230FT from some 700/900 series?



lummert
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Re: Excessive blow by with good compression?

Post by lummert » Fri Aug 16, 2019 9:01 pm

Does the oil dipstick push out due to the crankcase pressure? Maybe you're running an N/A engine with a +T. Maybe it runs best at 3 to 4 PSI. Maybe the crankcase oil breather box is clogged. Many things to check out.


1988 Volvo 760 Turbo Wagon

Gwbunce
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Gwbunce

Re: Excessive blow by with good compression?

Post by Gwbunce » Sat Aug 17, 2019 5:55 am

I had a similar issue with my 92 Turbo Wagon and it ended up being the crankcase oil breather box. It is under the intake manifold and is probably full of oil and not allowing the engine to breathe, also really clean up the pvc valve. And be sure you have the Turbo oil supply tube running the correct way.



Adam7917
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Adam7917

Re: Excessive blow by with good compression?

Post by Adam7917 » Sun Aug 18, 2019 1:53 am

It’s an n/a b230f +t. It sure is a fun car on 10psi I just have to take it easy on the highway. I cleaned the breather box and flame trap before the +t and used a new hose to run to the intake. The dipstick used to pop up and spray oil everywhere until I put on the vented oil filler cap. Upon further investigation, it will stay on 10psi on the highway in 5th gear for 5 or so seconds, but after that I think oil backs up in the drain from the turbo due to crank pressure and causes it to dump through the turbo/ into the exhaust. What would the next step in troubleshooting be? Pull the head and inspect gasket, valve seals, and valve guides? Leak down test? Is pulling the head even necessary?



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