Thread: Oil out dipstick tube, PCV mystery

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The 305 in my roadster pickup is blowing oil out of the dipstick tube at sustained speeds of 50 to 60 miles per hour---enough to really mess up the passenger side of the car. This is a chrome aftermarket dipstick tube, and chrome aftermarket dipstick. I know that the engine was not doing this when I pulled it from the donor car 16 months ago. I was trying to do some diagnostic work today, so I took my vacuum/pressure gauge, and hooked it to the dipstick tube. There is zero vacuum or pressure at the dipstick tube thru the full RPM range. I have a vented oil filler cap in the passenger side valve cover and a pvc valve in the drivers side valve cover, with a vacuum line running to the bottom front vacuum port on my 4-barrel quadrajet. I tested the vacuum on the port from the carb, and it is pulling 22 inches of vacuum at idle. I pulled the pvc valve (its a new one) out of the valve cover, and "sucked" on the end which attaches to the vacuum line, and it passed air with no restriction. This seems to tell me that there should be enough negative pressure inside a good running small block crankcase to avoid any kind of pressure build-up which would force oil out the dipstick tube. The only strange thing that I noted was that when the engine was idling and I pulled the hose off the PCV valve the engine immediately stalled.---Now---if I could suck air freely thru the pcv valve, then the carb should be able to suck air freely thru the pcv valve also. If the carb can suck air freely thru the pcv valve, then the engine should run the same whether the vacuum line is hooked to the pcv valve or pulled off of it. I don't really understand whats happening here.---any wise suggestions? I took out the dipstick and plugged the dipstick tube, then drove around to see if that really was where the oil was coming from-----there was no more oil showing up on the side of the car after that, and no oil leaking anywhere else.

O.K. Brian start over, plug the breather and re run your vacume test,still zero? then somewhere ya gonna be plugged up on the vacume side, & yes it should stall if ya pull the hose off the pcv " makes her go super lean " O.K. what about the pcv baffle in the valve cover, maybe pcv is bottoming out & shuttin it off???? or if custom valve covers sometimes ya gotta punch a knock hole open & install a baffle kit ???? but in any case the vacume is open all the way to the pcv valve,what about just simply a bad pcv happens all the time, or too soft vacume hose thats sucking shut (or kinked) Or wrong pcv valve for the application??? what evers goin on it's gotta be from the pcv valve to the inside of the valve cover.... Hey, my best pcv system test is simply a piece a celephane over the breather hole,with the engine at idle that cellephane should hold to the breather tube and then suck in slightly as the vacume builds, If it'll pass that test then your good ta go........

take the breather out of the valve cover, cover the hole and put your vac. gauge back on the dip stick tube, should have a vac. reading at the tube then.

It1s10---I tried the test you suggest. If I run the engine with the dipstick tube blocked off, and the oil filler cap removed, it will "suck" enough at the oil filler cap hole in the valve cover to hold a peice of paper in place over the hole, although I think it must be very little vacuum, because with the paper "sucked" in place over the filler cap hole, if I unplug the dipstick tube and put the vacuum gauge on it, it isn't pulling enough vacuum to register on the gauge.

There is a way to fix that if you are getting to much crankcase pressure.

O.K. Denny---Haven't tried the vacuum/pressure gauge on the dipstick tube yet, however, please enlarge on "the way". By the way, whats happening with your 1934?

Did some more diagnosing tonite----the wimpy hose that I have running to my pcv valve is collapsing under high engine vacuum. Tomorrow I will put on a better quality hose and see what that does for me.