Is there a test to determine the source of high oil consumption on the N16 engine?

Leaky diaphragm on the PCV system.

The Bentley manual says if the PCV system diaphragm in the valve cover is leaky, there will be high oil consumption. Has anybody seen this failure?

Valve guide seals versus piston rings

Historically, if you had high oil consumption, you could take the hose from the air intake off the valve cover and see if you got vacuum or not. If not, the blow by past the rings was greater than the PCV could flow and it was a piston ring problem. If you had vacuum, then then the PCV was working okay and the oil consumption was coming from the valve guide seals.

Per the Bentley manual, both sides are down stream of the throttle so I’m guessing you would want to check the hose at the back of the engine, (not the hose connected to the right side of the valve cover).
Thank you,
Peter

 

Yes.

Excessive crankcase pressures can cause excessive oil consumption. The TIS manual has you modify an oil fill cap with a nipple so you can connect a vacuum/pressure gauge an monitor the crankcase pressure; this is to test the PCV valve function. I don't remember the exact spec, but your gauge should be just around zero.

The problem with your "historically" example is the N16 engine is a valvetronic engine (variable valve life); there is almost no vacuum at idle where an typical american V8 or V6 might pull 18-20 inches of vacuum at idle.

Both sides of what are down stream of the throttle?

Compression and leak-down tests of each cylinder might help point you in the right direction.

 

Regarding crankcase pressure I found this:




The above from a MINI COOPER F56 HATCHBACK workshop service manual.

 

Wow. Internal vacuum of 0.02 bar is normal and 0.04 bar of vacuum is defective PCV. Pretty small number considering on a normal engine it might be twenty times that amount. I got about 0.04 bar but before I make a final decision, I need to verify the zero point on the gauge as these two numbers are so close to zero.

 

It looks like mine fluctuates around 0.035 bar so I’m going to replace the PCV diaphragm and hope for the best. At least it is a cheaper and less intensive solution than replacing the valve guide seals.

Thanks,😀
Peter