Owner experience, mostly from supercharged and track cars, not tests. How the standard breather system works and the other set-ups (PCV open or blocked, catch tanks, separators) are in Crankcase breather and PCV: options, catch tanks and oil in the intake.
- 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.
Help wanted
We don't have a measured comparison of outlet size, hose length or hose routing, or the fitting sizes owners used on a metal cam cover. If you have changed yours and measured the oil loss before and after, please tell us.