EDIT JimLev & I were composing in parallel it seems. His post is good. If you have a commercial gauge it would me more convenient.
EDIT2: My "MeasureWC.jpg" red arrows are wrong %^&*. As drawn, they indicate CCV pressure not vacuum. Sorry for the mistake.
There is no need for or benefit from a commercial slack tube manometer to measure CCV vacuum. (BTW, "slack tube" means that one end of the manometer is open to atmosphere - a fancy name for a simple idea)
A home brew slack tube manometer will give you a reading more than accuate enough at a fraction of the cost. All you need is a length of clear tube, a bit of masking tape, some water and a ruler. A tube size that worked for the diameter of the dipstick gude is labelled 0.375 ID, 0.5" OD (3/8 x 1/2)
BMW specs for the CCV are 10 to 15 millibar crankcase vacuum at idle, which converts to 4 to 6 inches of water column.
1 Wrap masking tape into a tapered plug at one end of the tube
2 Pour some water into the "U" of clear plastic tube so that you have say 8" on each leg.
3 Remove the dip stick and slowly insert the tape plug end of the tube into the dipstick guide tube while watching the water level change in the "U". Do this slowly since if the CCV is malfunctioning and pulling too much vacuum, it could suck all the water out of the tube into the sump. Not the end of the world, but would make an immediate oil change a wise idea.
4 With a ruler, measure the vertical difference in water levels in the "U." In my example, the red arrows on the MeasureWC.jpg. This is your vacuum in inches of water column.
In step 2 you want to be sure to have enough water in the "U." Say you start with 2" each side and your CCV is pulling 6" of vacuum. All the water will be pulled into one side of the "U" for a total of 4" w.c. which is not enough to resist the 6" w.c vacuum from the crankcase. The slug of water could be pulled into the sump, unless you quickly yank the tube off the dipstick guide tube.
The high water will be on the engine side of the "U" for vacuum. If the high side is on the open end, the crankcase has pressure indicating a failed CCV.
A few extra feet of length as in my example is a good idea. If you have a high vacuum & the water starts rushing toward the engine, you will have a second or two to pull the tube off the dispstick guide tube before the water is sucked into the sump.
This measurement is not a definitive test of the CCV.
If the CCV has sludge &/or water, it could misleadingly pass or fail depending on whether the water is frozen or not and whether the orifice valve is blocked.
Prolonged driving in ambient temperature that enables the CCV & hoses to get good and hot might clear a sludged up CCV. But, you risk engine damage before the sludge cleared.
Conversely, a CCV with sludge that passes when warm/hot, could freeze up in cold conditions & cause problems.
Last edited by rdl; 04-12-2011 at 09:16 AM.