Need help with major oil leak...

[Slonaker]

To make a short story long, my 305 blew a quart of oil all over the bottom of the truck in a 25 mile trip several months ago. I couldn’t figure out where the oil leaked from because everything on the truck leaked at the time. I was about to pull the engine apart, so I did not really worry much about the leak, especially since it never happened again in several hundred more miles of driving.

I recently replaced my cam, pushrods, lifters, and all the seals and gaskets in my engine except for the rear main. I figured that whatever leaked that one time would have been fixed, but it was not. It has now lost a quart of oil in a 60 mile trip, and almost a half a quart in a 25 mile trip.

The truck runs well, and does not leak on my driveway. It does not leak while idling. When I drive it, though, it covers the entire bottom of the truck with oil. The oil appears to be coming of the back of the engine because the front ¾ of the engine is clean. The oil is not leaking from the intake or the valve covers, both of which have new gaskets anyway. The oil pressure sending unit is new, replaced while I had it pulled apart, so that seems to rule it out. It appears to be blowing past the rear main, but only while driving.

I talked to a mechanic friend about it, and he says that a malfunctioning PCV valve will cause a SB Chevy to blow oil past the rear main while driving. This weekend I replaced the PCV valve and the hose that connects it to the carb. I have verified that the PCV rattles and is connected to a good source of vacuum at the front of the carb. When I disconnect the PCV valve from the hose, the engine immediately dies from the massive vacuum leak. I also made sure that the aluminum tube that goes from the valve cover to the air cleaner is clear and clean, and replaced the rubber seal at the valve cover and the rubber hose at the air cleaner.

After all of this, it is still blowing past the rear main while driving. Remember, it does not leak on my driveway, and there are no visible leaks while idling. I cleaned everything up around the rear of the pan this weekend, and with 20 minutes of fast and slow idle in the driveway, there was no visible leakage.

Does anyone have any suggestions about what might be making it blow past the rear main? Is there anywhere else it might be coming from?

Slonaker