PCV Positive pressure

[Fuzzpro]

Hi, first of many questions, no doubt. Hopefully I can give back a bit too.

I've just purchased a 940 Wentworth 1993 with the B200ft and 4 speed manual with overdrive. Around 100,000 miles.

When I went to look at the car it was breathing a little through the filler cap. I put this down to the old seal, it was also quite wet around the bottom of the dipstick area. have since read into it a bit more and found out about the clogged PCV issues. So i ordered a new oil trap and set about cleaning out the system. It was blocked solid!

After clearing all the pipes and fitting the oil trap i still have positive pressure as the filler cap bounces around and doesn't suck down. Is there anything i may have missed? It doesn't have a flame trap. I didn't do anything with the oil drain tube as everyone says don't touch it. Could that be blocked?

I also didn't have a replacement o-ring so popped on one that looked about right and added some instant gasket but it appears to be throwing oil out of the oil trap where it meets the block. I assume that's probably down to the wrong o-ring so I've ordered the correct one ready to fit.

I'm happy to drop the sump and replace that pipe if needed and do an oil change and flush even though it's just been done before I bought it.

[Forrest]

The problem with the crankcase breather is usually the small hose from the inlet manifold to the y-piece. This gets very blocked with hard carbon deposits and perishes. Without the vacuum drawn through this the PCV doesn't work.
Replace the small length with some genuine Volvo hose. If you use cheap hose it won't be heat resistant and won't last long.

Remember you will probably need to clean out the y-piece (careful not to snap the small leg off) and the nipple on the inlet manifold too. Suitable sized drill bits can help with this.

A proper Volvo o-ring will probably solve your oil leak at the oil trap. The green o-ring fits in a groove under the oil trap so one the wrong size won't work and garming it up with RTV won't work either.

Before making rash statements about dropping the sump maybe take a look at what would actually be involved with that. It is a non-trivial task on these cars and you will probably need some means of lifting the engine from above in order to achieve it.

Useful part number below. Some may be NLA from Volvo but there are third-party alternatives out there.

Oil trap, 3501160
O-ring, 949659
Breather hose, 3507245
Small vacuum hose to inlet manifold, 976734
Hose from y-piece to oil trap, 949701

[Fuzzpro]

Thank Forrest.

Yes, everything, especially the small hose were blocked. I cleaned out the small hose, the plastic Y piece. The large hose and the nipple that goes in to the manifold and I replaced the oil trap. All of it was clear when I refitted it.

I was hoping there might be something I'd missed in the system. I'll replace that small hose as it was just starting to show signs of age but it is intact.

I did try to find instructions on dropping the sump with a quick Google but nothing came up. I assume it's not as simple as I'd hoped then?

[Chris1Roll]

Have you 'glove tested' it?
If everything you say is clear, it should be sucking like a Vegas hooker- that pipe ro the sump goes below the level of the oil so even if it is blocked, it won't make the crank pressure positive.

Be careful with the glove test, I nearly lost one inside the other day! But just using the filler cap to test, I couldn't really be sure.

[Fuzzpro]

I haven't glove tested it, no. I've replaced the small vacuum hose now, it was definitely showing it's age.

I'm waiting for the new O-ring to arrive then I'll test once that's fitted and hope for the best.

The seal in the filler cap has definitely sorted that leak though.

[Fuzzpro]

Quick update. I've replaced the O ring with the correct green Volvo item and no more leaking oil trap. Also runs a lot nicer now. Also replaced the small pipe too.

No more oil leaks for now.

[Forrest]

Sounds as though you’ve probably sorted it. Well done.

If it’s been run for any length of time with a faulty PCV it may also have affected the radial oil seals on the engine. They may settle down of their own accord. If not, replace the front ones at the next cam-belt change.

1 x 1276425 - Crankshaft
2 x 6842273 - Camshaft and intermediate shaft

Of these, it is only really the cam seal that will cause you any real problems. If it’s leaking then you will get a small trickle of oil over the top of the water pump. This will be sufficient to rot the top sealing washer on the water pump and ultimately lead to a coolant leak.

I use genuine Volvo seals and the correct insertion tools for a reliable fit every time. Whack non-OEM seals in with a similar sized socket if you like to gamble.

[TonyS9]

These engines have no check valve in the breather system, it should definately be fine in idle and suck, but on boost (especially with extra boost) the dump on closed throttle does pressurised the crank briefly via the large pipe on the inlet and generally causes oil leaks. This is why B2xx turbo engines are more oily than non-turbo engines. Some engines are OK, but all leak on extra boost dumping and can spurt oil from nearly every seal and gasket.

Other run an open oil can, but I am trying to maintain environmental complaince. I've tried fixing this with a check valve but used too small a one creating too much pressure on boost (from blowby). Havn't found a good solution yet.

[Arthur1330]

Originally Posted by TonyS9

These engines have no check valve in the breather system, it should definately be fine in idle and suck, but on boost (especially with extra boost) the dump on closed throttle does pressurised the crank briefly via the large pipe on the inlet and generally causes oil leaks. This is why B2xx turbo engines are more oily than non-turbo engines. Some engines are OK, but all leak on extra boost dumping and can spurt oil from nearly every seal and gasket.

Other run an open oil can, but I am trying to maintain environmental complaince. I've tried fixing this with a check valve but used too small a one creating too much pressure on boost (from blowby). Havn't found a good solution yet.

I use this check valve (14mm version for AN10 hose) on the return to the intake pipe before the turbo, from my catch can. Stops the leaks out of the oil cap and has been fine for 1k+ miles or so! Took around a week to arrive, but the shipping is as much as the valve itself unfortunately...

https://www.uprproducts.com/upr-pro-...ting-pressure/

I did previously use a cheap eBay one, and that got stuck and I ended up with a lot of oil out my filler cap!

[Fuzzpro]

Interesting, I am running a MBC and at around 12psi.

I've been looking at catch cans and similar assuming that at above standard boost on a 30 year old engine I'd have a good bit of blow by.

It turns out, I have very much improved it, but not fixed it. It still leaks at the base of the dipstick tube. Is this removable and is there a replaceable seal there.