For awhile now my 01 a6 4.2 has had an intermittent oil leak. The main leak is it the back of the engine on the passenger side just below the valve cover. Once in awhile it will even leak from the oil cap and has even blown the dipstick out once. Replaced the valve covers awhile back but did not replace the "half moon" blue rubber peices as I did not know where they went. I noticed a cut out in the back passenger side, under the valve cover with a yellow rubber plug in it but the plug is recessed about a half inch into the engine. Wondering if its supposed to be sunken in or if its supposed to be flush with the outside of the engine? Also is there a common issue that causes extreme crankcase pressure?

 

A clogged PCV could very well cause this. Also, yes, the half moon piece should be somewhat recessed when feeling it from the outside. You're probably leaking oil from the cam cap, not the half moon piece, but I would still replace both for good measure.

Get yourself an inspection mirror to confirm.

 

Thanks so much. I think I found the culprit. Same thing happened today on my way home from school, as soon as I got home I took the crankcase vent apart and sure enough it was filled with ice and sludge. It's been ridiculous cold, like the past 3 months have averaged in the -30's with some days in the -40's even a few -50's. there have been news articles statingManitoba has been colder than the North Pole and the planet mars... Lovely I know. I guess with the extreme temps and short drives I've gotten too much moisture in my oil. Oil will be changed this weekend and hopefully it warms up! So if you have a vent problem and you're driving on the surface of mars, check for sludge in your pcv/crankcase vent!