Fixing to work on a buddies 96 p pumper and need a little help. He drives about 20 miles to work and when he pulled in there was a wonderful oil slick, Waited about 5 hrs. checked oil and it was 3 qts. low. Seems to only be leaking bad(still doing it) when hes running at hiway speeds (2200-2400 rpms) he said if he putts around it doesn't seem to lose any.looks like it coming out of blow by tube but not sure, gotta do alot of washing. He's had this truck about 4 yrs. with no problems at all, uses about 3 qts. between 8k-10k oil change, had not noticed anything out of norm just started all of the sudden. Truck has 225k on it, no mods 5 speed. Could this be vacuum pump out pumping air into oil pan? Thanks guys

 

Probably the vaccum pump pressurizing the crankcase.