1996 850 boost pressure into crankcase/ one way valve.

tardcart · Post by **tardcart** » 08 Feb 2019, 16:43

I replaced the crankcase vent system and still have oil seeing out the cap under 12 psi boost. I don't see any posts on this but correct me if I'm wrong- under boost the intake is at 12 psi and the vacuum line back to the pcc (If thats what its called) heater into the intake
hose is pushing 12 psi that can't exit the small oriface in the pcc. so it goes back through the crankcase vent and pressurizes the crankcase. I see mention of drilling out the pcc, but what about a one way valve on the vacuum line to the intake, or a one way line on the crankcase vent line? (maby refit a pic valve from chevy v8?) some thing to keep the 12 psi from adding to the block pressure under boost. My car is low miles and owned by old lady so doubtful out of spec for normal blow by. also any body dicker with a large vacuum accumulation can like hot dodders use for their vacuum breaks? probably would be pissing in the wind.

Post by **FlyingVolvo** » 08 Feb 2019, 17:03

If you're PCV system is good to go (double check with glove test over dipstick with warmed up engine), this may be a dumb question, but how old is the rubber oil cap seal? Even if you're not getting bad crankcase pressure, those things will leak if old and worn out.

Post by **misha** » 08 Feb 2019, 17:51

I would say that you connected hoses wrongly or didn't cleaned ports on the block.
If that checked ok....than seal on the oil cap needs to be replaced.

tardcart · Post by **tardcart** » 09 Feb 2019, 06:24

good advice for the symptom, but it seems to me the engineering never accounted for boost pressures past stock, and and then only for short bursts.
Im looking for a way to keep 12 psi at the manifold from going down the vacuum line to the
Ptc valve and pushing back through the crankcase vent into the engine, only slightly reduced by the small hole in the pic that vents to the intake. one way valve on the vaccuum line? any one tried that? It seems to me under prolonged boost the the pressure in the crankcase will be half the boost pressure (since the hole in the Pic is the same size as the vacuum line), plus blow by. thats too much.

Post by **abscate** » 09 Feb 2019, 07:18

but it seems to me the engineering never accounted for boost pressures past stock, and and then only for short bursts.

>> that's how Good engineering works, actually.

Post by **erikv11** » 09 Feb 2019, 07:49

tardcart wrote: ↑08 Feb 2019, 16:43 ... My car is low miles and owned by old lady ...

Then definitely check for blocked ports where the oil trap meets the block, barely driven cars in cold climates are the worst for PCV buildup. But this is almost surely just an old cap gasket. They go bad in a couple years, is this one 20 years old?

Post by **abscate** » 09 Feb 2019, 08:11

Added presumed year model to title

Sommerfeldt · Post by **Sommerfeldt** » 09 Feb 2019, 09:08

It’s also worth noting that the 850 actually IS engineered for a stock boost level of 12 psi. It’s the factory level for both the T5-R and the 850R.

It’s also hard to see how anything can be pushed back in any way - the intake tube is sucking enough air to create that pressure inside the engine, and everything only has one way out, so to speak. If the PTC is clogged or too small, you’ll have a pressure buildup, but not a return. Only a diminished pressure relief.

- S

Klausc · Post by **Klausc** » 09 Feb 2019, 10:28

When under full boost, the intake manifold pressure is positive to 12psi, so the small PCV line from the cyl 1 area to the PTC should be positively charged. But the amount of air passing through the air intake to the turbo creates enough vacuum to draw air from the large line to the PCT that it will draw air from the crankcase. If the PTC is clogged (glove test failed), do not DRILL it out. The heated portion is soft copper and you don't want to ruin it. I used a stick made from oak to clean out the core. Be careful not to damage the rubber base during removal and make sure it is seated properly against air leaks.

The oil cap gasket is only good for a couple of years at most. Once it gets hard, it will leak regardless of crankcase pressure.

tardcart · Post by **tardcart** » 09 Feb 2019, 15:39

I don't know why people would argue there isn't 12 pounds of boost plus blow-by at the PTC diminished only by the small hole in it and
the very slight vacuum present in the intake tube, thus pushing back into the crankcase. any thoughts or experience with a one way valve on the vacuum valve from the intake? I notice there is one on the charcoal canister line off the throttle-body tree. Im not really discussing maintenance issues, just how pressure in the crankcase can be better relieved in what seems an inadequate system under any boost, let alone increased and long duration boost.