Crankcase vacuum

[Shrek]

What should be the correct vacuum reading at the oil cap.  I changed oil and filter today.  Started the engine to get thing flowing and it ran very rough.  Put the oil cap back on and everything smoothed out like normal.  Which raises the question of what is the correct vacuum level at the oil cap at idle.  I do know a failing AOS can be detected by a higher than normal vacuum level at the cap.  So now I plan to fab a cap with a fitting to measure crankcase vacuum level.

[JFP in PA]

You need to tell us your year and model of the vehicle as they are different.  Assuming you are speaking about the 2003 in your records, you should be reading around 5 inches of water or less at the oil cap when fully warmed up.  Note that is inches of water, not mercury.  If it is higher than that, your AOS is probably on its way out.

[Shrek]

Once again thanks.

[Shrek]

OK, finally got a 0 - 30 inches of water vacuum gauge and fabbed up an oil cap.  At operating temp at idle I read 5" of vacuum.  The AOS had been changed on this car twice previously.  One of the reasons I went with this 2003 Carrera is it came with complete maintenance records from the day it was initially sold plus the IMSB and RMS had been updated.

[JFP in PA]

Then your AOS is fine.  We checked every car that passes thru the shop for this vacuum level, just as a precautionary measure as the cars tend to show higher vacuum levels for a bit before they become problematic and need to be changed.