Volvo: oil blow by, crank case, ventilation system

Question
I have a 1993 850 and it started leaking oil. what I found is that when you drive it oil pressure builds in the motor causing oil to come out the filler cap and if you pull up dipstick right after driving you get a guss of presser releasing form there

Answer
Mark,
Your crank case ventilation system is clogged and that is the cause of excessive pressure in the crank case. The flame shield (or PCV) is located in the air tube that goes into the throttle housing. It has a large hose about 12 or 13 mm, and a small one about 3mm going to it. It twists about a 1/4 turn into the tube and is replaceable. Buy the plastic nipple, the flame shield and the o'ring. Also get a new oil cap seal and o'ring for the dip stick.