Car Burning Oil, Crankcase Pressure Twice The Spec
Hello everybody, we have this car with all the signs of possible bad valve stem seals: oil consumption, smoking quite bad (worse at start-up, worst after prolonged idling). We are trying to eliminate all other causes before proceeding. We initially suspected a faulty PCV valve: Crankcase pressure is measured at 42 millibar, which is nearly twice the specified value (22 millibar, link to TBS below), so the valve cover was replaced. The excessive crankcase vacuum persists. Cylinder leakage test is good, btw. Tips and ideas appreciated.
Link to service bulletin: tsbsearch.com/MINI/SI-M11-07…
Peter, Have you tried blocking off the vacuum to the PCV system and see what crankcase pressure is? If you are still building a vacuum then the issue is internal to the engine. If not then you may have a defective brand new valve cover. HTH
Thanks for the input, Rick. I blocked off the vacuum pump after the initial test, and the reading went down to around 29 mBar.
Isn’t that gauge showing crankcase pressure? Wouldn’t a vacuum show NEGATIVE ? I think the cylinder leakage test should be done with more air pressure to be an accurate Indicator.
I agree, the leak down should always be done with 100psi. At 30 psi the leakage would be low.
Hi Gary, I like to start low and build up pressure from there. As I understand it, thin valve stems may flex under max leak-down pressure and hide valve leakage. (Speaking generally here, not in reference to the OP's oil consumption concern.)
Thanks all, good idea with a higher pressure. Our compressor can't crank out more than 30 PSI. I will have to do something about that. Rusty: You're right, value should been displayed as negative. I switched the tubes around. The tube connected to the crankcase is at a lower pressure (ie sucking more air) relative to the atmospheric pressure.
Do you have the wrong valve cover? that pressure would be in spec for a b48 engine according to the bulletin.
Cylinder leakage spec is very low for mini. I think it’s around 8% any more than that it’s toast.
Crank up the leak down tester, but also some of these guys change there oil every 15k and wonder why they smoke it can take a few oil changes at 5k to get it working again some recover but some dont
Shop pressure is 30 PSI. I may have to look for another compressor.
Hello everybody, we have this car with all the signs of possible bad valve stem seals: oil consumption, smoking quite bad (worse at start-up, worst after prolonged idling). I am absolutely not an expert on evaluation of oil consumption issues; however, I believe that your continuing to see smoke, or smoke worsening as the car continues to idle, may well indicate a piston ring problem (oil…
Hi Andrew, thanks for the thorough response. We might have to do a leakage test at a higher pressure than the previous 30 PSI. Perhaps that will give us clues on where the pressure is going, if anywhere at all. We have a excessive vacuum/underpressure, and I'd like to think (and hope) that the PCV built into this new valve cover is not faulty.
It's not mentioned in SI, but if you want an accurate crankcase vacuum reading, disable the valvetronic. On most engines, unplugging a vanos solenoid is enough to revert to throttle control, but you may need to unplug the valvetronic motor with the engine off.
I'm not familiar with this engine, but I read somewhere that the vacuum pump actually exhausts into the crankcase, so the vacuum pump shouldn't cause underpressure, if this assumption is correct. If I disconnect the vacuum pump and block off the outlet into the crankcase, the vacuum drops from 42 to about 29 millibar, not far from the maximum 26 mBar allowed in the spec. Can the oil that's…
I disconnected the vacuum line from the crankcase and blocked off the tube (see attached image). The valve cover we installed is an aftermarket, though the original BMW valve cover had the same amount of vacuum. Both valve covers could be faulty, but I think my next step is to find a way to test the vacuum pump.