Crankcase breather and PCV: options, catch tanks and oil in the intake

How the standard system works (one owner's explanation)

• Excess gas and oil vapour leaves through a port in the cylinder head between the inlet ports, goes through the PCV valve into the inlet manifold, and is burnt. Fresh air is drawn in through the cam cover, from the intake pipe after the air filter, so it is filtered.
• At full throttle, or on boost, the PCV closes, because manifold pressure would otherwise pressurise the crankcase. The flow then reverses and some gas and vapour leaves through the cam cover. The same owner said that is not the intended design and that 99.9 per cent of these engines never run at full throttle for long.
• Blocking the PCV port leaves a single vent, the cam cover, with air trying to go both in and out of the same hole. The same owner said that causes "bumping", like a full bottle held upside down, with oil ejected in pulses.
• On a supercharged car the PCV was blocked on the specialist's map because that map could not be set up with it connected (it caused a high tickover). The Dutch OBD Tuner software lets you choose. One owner quoted the software maker as saying you only need a part-throttle fuel learn after unblocking it, and that he had never heard of problems with oil from the system, but that the original cam cover vent is small for big power. Treat this as second hand.

The set-ups owners tried

1. PCV open, cam cover hose to the intake pipe (standard layout)

• Several owners reported a clean intake after hundreds of miles and track days. One said a few hundred road miles and a track day left the inlet "clean as the day I put it on" two years later (with a separator in the line). Another had a thin smear of oil in the charge cooler after a track day, and one with a Saab engine said his car and the intake were covered in oil.
• The worry is oil reaching the charge cooler fins on a supercharged car, and diluting the fuel. One owner said oil and sludge lowers the fuel's octane. That is theory.
• If you do this, put a decent separator or catch tank in the cam cover hose, or use a separate small air filter, as one owner advised.
• One owner recreated the factory layout differently: a small brass take-off with a 1.5 mm hole drilled and tapped into the cam cover, a 3 mm hose to a brake servo one-way valve, and the hose into the air filter pipe. He reported no oil in the filter housing after two hours of hard driving. It is one owner and one short test.

2. PCV blocked, cam cover vented through a catch tank

• The common track set-up. Some owners get almost nothing in the tank over thousands of miles. Another with a track Z22SE filled a 1.5 litre tank in 2 to 3 track days. Another said one supercharged car needed its roughly 1/2 litre tank drained once a track day.
• Many cheap tanks are empty boxes with the inlet and outlet close together, so they separate nothing. Owners said to add a baffle and steel wool, making the gas pass through it. One owner did this with a copper tube down to the bottom and steel wool in a section cut from a food can.
• What collects is often oily condensed water. A cold metal tank in an engine bay condenses water, and one owner suggested keeping it warm so the oil separates from the water. Draining the tank back to the sump was debated: one owner said it only returns water, another said the sump heat evaporates it and it just refluxes. The better separators have a heated drain back to the sump, and a one-way valve was suggested in the drain.
• Venting to atmosphere. Several owners said it is fine, and that cars did it before emissions laws. One said his first hose position gave an oily smell in the cabin, and that extending it under the car into the airflow cured it. Another warned that it is an MOT fail in the Netherlands, and the UK rule was not stated. It also drools oil, and race and rally use requires a catch tank. Put a small filter on the end if the line can draw air in, which it will at idle and part load.
• Owners also mentioned heavier-duty separators: a cyclonic BMW-type unit and a Mann-Hummel Pro-Vent 200 (one owner said it is used on modified GM V8s). Others suggested maze or swirl separators from V8 parts.

3. Extra or bigger vents

• The timing chain inspection plug. One owner fitted an M22 x 1.5 to AN-12 adapter, ran both it and the cam cover hose into a catch can and out to a small filter, and had no oil in the can after a month. The idea is a bigger vent so crankcase pressure cannot build up. He kept the manifold PCV in place.
• A vented oil filler cap was suggested. Others pointed out that it bypasses the oil separation inside the cam cover, and one owner thought it would not fit under the standard cover.
• The turbo oil return port on a Turbo. One owner said a vertical pipe of about 12 inches from that port, topped with a catch tank or a gauze breather, is an option, because it sits well above the sump oil level. On a Saab block the turbo return hole is an option as well. Do not block the three channels between the cam cover and the crankcase: an owner said that would pressurise the crankcase if there is any blow-by.
• Hose loop. One owner on a Stage 2 supercharged car ran the rocker breather to a catch can, then to the air intake with the hose looped high above both, and reported no oil in the intake and very little in the can.

Venting the cam cover to atmosphere: size, hose length and the oil filler cap (2009 to 2012 threads)

• The standard outlet is small. One owner measured it at about 8 mm inside, another remembered about 9/16 inch (roughly 14 mm), so the sources disagree. Owners who fitted a bigger outlet reported fewer problems: one blanked the original and fitted a 15 or 16 mm fitting next to the inlet manifold and said the breather problems went away, and another drilled and tapped a new, bigger hole in the metal cam cover and put a filter straight on it, after filling a catch tank before. The GM Ecotec build book was quoted as recommending at least -12 hose. A plastic cam cover can't be enlarged this way.
• Why bigger. One owner said a supercharged engine that vents only through the cam cover relies on blow-by to push the gas out, so any resistance in the pipe matters, and that resistance rises with the square of the flow (double the flow, four times the pressure drop). Another could not see why an open pipe gives resistance. The explanation offered was a straw versus a hose.
• Hose length. Owners disagreed. One said the pipe should be short, because blow-by climbs steeply with revs and a long thin pipe adds resistance. Others said the length makes little difference if there are no kinks or restrictions, and ran theirs 1.5 metres to the diffuser or over the subframe and out behind the rear wheel, for tens of thousands of miles and dozens of track days. One owner who extended his pipe under the diffuser found much more oil on the diffuser, and wondered if the airflow was sucking it out. Others doubted that. Hose ends near the front of the car drew fumes into the cabin, and an end near the rear wheels can mist the wheel and rear of the car.
• An extra vent through the oil filler cap was fitted by a few supercharged owners on plastic cam covers, with a 19 mm 90-degree elbow and hose, then a filter away from the boot lid grille. One owner reported no oil lost at Snetterton afterwards, and another said minimal venting, just a little in the pipe. Others warned it bypasses the baffles in the cam cover, so it may mean more oil loss. The cap's internal valve has to be removed, and sealing the elbow with a flexible sealant lasted better than epoxy for one owner.
• Metal and plastic cam covers. The covers on the Saab-engined cars are metal, and the Z22SE type are plastic. Oil that reaches a breather filter in the intake can fill it and drip down the front of the engine bay and undertray, which could hide a real oil leak.
• Condensing in an oil cooler. One owner suggested a hose to an oil cooler mounted higher than the breather, so vapour condenses and runs back to the sump. The owner with the problem did not want condensate in his sump, and another said to stay with venting to atmosphere so that condensates do not drop back into the oil.
• Sources of oil in a heavily breathing engine. Forged aftermarket pistons were said to give more blow-by. One owner said a car using about 1.5 litres at a track day lost almost all of it through the breather. Another said that oil changed to a 10W50 or 10W60 (and, for one, a 10W40) greatly reduced heavy breathing, while another said the engine was never designed for thick oil, and that what matters is low volatility, for which an oil claiming the MB 229.5 approval was suggested. These are owner opinions.

Turbo notes (2016 thread, Z20LET)

• An owner said the turbo needs no different approach from the supercharged Z22SE, as blow-by scales with power, so any system gets overwhelmed as power rises.
• On the Turbo the crankcase vent pipe (separate from the cam cover outlet) is the main source of positive pressure. One owner with a heavy-breathing engine took one feed from the crankcase and one from the cam cover, each into its own separator, and later only the crankcase one once the engine had run in, with the cam cover outlet blocked. Another owner said the cam cover outlet is the best place to take fumes, because the cam cover has galleries that remove oil. Both views were posted as opinion.
• Many VXR owners put a breather box from the Omega and other models between the crankcase outlet and the cam cover.
• One owner runs a Mann-Hummel Provent 200, bulkhead mounted by the air intake (about 220 x 150 mm), which drains back to the sump. The install instructions, as another owner reported them, need a check valve and a minimum 350 mm column between the oil outlet and the crankcase inlet. Return routes mentioned: the turbo return bung on the B207, or brazed tees in the dipstick tube. Another owner suggested a drain plug nozzle tapped into the block with a one-way valve.
• An owner whose old engine had blown rings (burning about 0.5 litres in 150 miles when driven hard) said that venting the crankcase to atmosphere through a large separator is best for the engine, and listed the drawbacks: it may fail an MOT (he said it conflicts with Euro 4), it can smell, and it leaves an oily film on the car.

Oil around the inlet manifold gasket

One owner found oil coming from the PCV hole in the cylinder head past the inlet gasket after a track day, in the manifold and the charge cooler. His inlet bolts were found loose too, which may have contributed. An owner suggested filling the hole with alloy putty (not silicone), and trimming the cam cover gasket so that oil does not build up in the channel above it, since that build-up causes the problem. Another owner temporarily blocked his as a test.

Oil choice

One owner said a thicker oil (a 50 or 60 grade) should reduce blow-by and so crankcase pressure. Another replied that the engine was not designed for it and it stresses the oil pump and chain or belt. One owner changes oil often, four times in 13,000 km, and says the engine is clean. See oil and filter change.

When a lot of oil is coming out, it may be blow-by

A Z20LET, Stage 4, 32,000 miles, was pumping oil out of the cam cover breather into the intake when the turbo was boosting, after the large breather hose had clogged because its layers separated. The hose repair did not stop it, and nor did a 10W/60 oil or a catch can.

• An owner said it is either positive crankcase pressure (gas past the pistons and rings) or leaking valve stem seals, and the first fits a dramatic flow better.
• His test: disconnect the crankcase hose (the 90-degree bend) at the cam cover, run the engine to about 5,000 rpm, and a good engine gives little gas. For a better test, route the open hose into the cabin and feel the pressure under hard acceleration. A compression or leak-down test will confirm.
• The hose stopping when reconnected means nothing: another owner pointed out the flow was only being redirected. The owner's engine came out and all the piston rings were more or less cracked. Another owner had lost about a litre of oil from the breather in two laps on track, and another had smoke everywhere at Dijon, with cracked or broken oil rings, so it is a known cause.
• The advice for the rebuild was to hone the bores and fit new rings (and pistons if needed), and one owner said pistons and rings can be changed with the head and sump off, without removing the engine or the clam. See engine oil leak: finding the source for the other places oil comes from.