Positive crankcase pressure

roy1956 · Post by **roy1956** » 12 Jun 2017, 21:36

I have a '95 850 Turbo with 312,000 that I have owned since new. I am noticing a puff of smoke in my rear view mirror when I take off after sitting at a red light for a minute or two....which is the reason for this post.
Although I recently changed the PCV/oil trap plumbing, I am not passing the rubber glove test as described by Robert on youtube. In fact, when I put a rubber glove on the oil filler, it inflates slightly. I am getting oil seepage out the weep hole between the engine and transmission. The rear main seal was changed a couple of years ago so I know it isn't that. My suspicion is that the positive crankcase pressure is forcing oil out the rear main seal and perhaps down the valve stem seals (which haven't been changed). I have checked the ports in the block where the oil trap and other fittings go into the block and there is zero carbon in the openings. Also, just to be sure, I hooked up a length of hose to each of the ports and was able to blow air through them with no problem. I am out of ideas as to why I am not getting scavenging vacuum in the crankcase. I think the positive pressure may what is causing both the oil issues. BTW, the engine recently had a compression check and all cylinders are at 95% with one at 90%. The mechanic said it is in great shape for so many miles.

Anyone out there have any thoughts or ideas on any of the above?? I would be most grateful for any feedback!! Thanks!

Post by **kahl** » 12 Jun 2017, 23:42

Just for giggles switch the hoses on the top of the oil trap box. Just give it a try.

Post by **tryingbe** » 13 Jun 2017, 06:56

I found with the older engines, even with new PCV parts, it is not enough. The stock PCV pipe from the separator to the intake is severely undersized for an older engine. Also, the hole at the heating element at the PTC valve is tiny, like smaller than 1/4 inch tiny. Both will restrict the flow of the crankcase gases.

To address those issues, here is what I do. Get the below parts.

A 3ft 5/8 oil compatible hose. Do not use silicone hose, as it will "sweat" oil. Do not use heatercore hose, it is not rated for oil, it will become soft and you'll have to replace it sooner. This is what I use. Buy 3, as it is sold by the foot.
http://www.ebay.com/itm/291442927889?_t ... EBIDX%3AIT

One 3/4 elbows from your local hardware store. (5/8 will be the wrong size!)

A 3 feet 3/16 inch or 1/4 inch vacuum hose to replace the small hose from the intake manifold to the PTC valve. I prefer silicone hose for this.

Optional, get 6 of this. I like their clamps.
https://www.ipdusa.com/products/4768/10 ... 12mm-width

Optional, wireloom to protect the hose.

Take a unibit and drill out the PTC valve holes to as big as you feel comfortable. I think I drilled mine out to about 1/2 inch.

Remove the intake manifold and replace that stock PCV hose, I cut a short hose and then use a 90 degree elbow, than a long hose to the PTC valve. Replace the vacuum hose to the intake manifold to the PTC valve with the new one. Then reinstall the intake manifold.

All the crankcase gas have to go thru that tiny PTC hole!!!

Installed on car

Post by **Chuck W** » 13 Jun 2017, 07:04

The wife's '97 GLT LPT is kind of same way. Did the PCV system maintenance and still have the slight bit of positive crankcase pressure. I had been thinking about getting a Mann ProVent set-up, but this looks like it'll be a good solution.

Post by **ZionXIX** » 13 Jun 2017, 14:56

tryingbe wrote: ↑13 Jun 2017, 06:56 I found with the older engines, even with new PCV parts, it is not enough. The stock PCV pipe from the separator to the intake is severely undersized for an older engine. Also, the hole at the heating element at the PTC valve is tiny, like smaller than 1/4 inch tiny. Both will restrict the flow of the crankcase gases.

Have you noticed a substantial change after the modifications? Im convinced that my increase in crankcase pressure is due to blowby since my PVC box was squeaky clean when I changed it last. Do you think there will be any negative side effects to this mod? like spark plug fowling from extra oil getting into the cylinders due to increased air flow? Im totally game if this works.

Post by **erikv11** » 13 Jun 2017, 22:04

Many, many people have re-plumbed their PCV system using this concept. Most of them used other (inferior) hose though, the one recommended by tryingbe is excellent. At any rate I din't see any side effects in my cars, and I don't know of any. The biggest risk is probably if the large hose kinks under the intake manifold where it makes a 90 degree bend, blocking the PCV. But with the right angle adapter (see above) that's not an issue.

Even with a squeaky clean PCV box be sure to check the drain ports behind it, into the block.

Post by **tryingbe** » 14 Jun 2017, 06:58

ZionXIX wrote: ↑13 Jun 2017, 14:56
tryingbe wrote: ↑13 Jun 2017, 06:56 I found with the older engines, even with new PCV parts, it is not enough. The stock PCV pipe from the separator to the intake is severely undersized for an older engine. Also, the hole at the heating element at the PTC valve is tiny, like smaller than 1/4 inch tiny. Both will restrict the flow of the crankcase gases.

Have you noticed a substantial change after the modifications? Im convinced that my increase in crankcase pressure is due to blowby since my PVC box was squeaky clean when I changed it last. Do you think there will be any negative side effects to this mod? like spark plug fowling from extra oil getting into the cylinders due to increased air flow? Im totally game if this works.

The modification works for my car.

Post by **erikv11** » 14 Jun 2017, 08:05

roy1956 wrote: ↑12 Jun 2017, 21:36 I have a '95 850 Turbo with 312,000 that I have owned since new. I am noticing a puff of smoke in my rear view mirror when I take off after sitting at a red light for a minute or two....which is the reason for this post. ...

Oh, I missed your opening sentence: PCV issues aside, the puff of smoke is almost certainly due to worn out valve stem seals. Like 99.99% chance.

Post by **Clemens** » 14 Jun 2017, 12:33

I'd also suggest the bigger tube to the ptc nipple. I had the same issue you had after doing the pcv system the first time and after doing it again with the mod the problem was gone. Also, male sure that the top hose under the spark plug cover sits correctly, mine came off a few times due to a clamp that was too wide. That reduced the vacuum.

As for the weep hole: if the RMS was replace a few years and the pressure was too high ever since, your RMS might be leaking again. After getting good vacum try to run a bottle of ATP 205 for a few thousand miles. This has cured my leaky RMS with 200.000 miles on it completely. Just leave it in there long enough. Took like a month or so.