I bought my current F-150 last October. When i originally made the purchase i did so with it having a few minor oil leaks and running pretty rough. The carb was in pretty sad shape and it blew oil from the pcv system.

Now, that i've had it a few months, the truck is in great shape. I replaced the carb, gave it a tune up and all that. Things were wonderful, and for a brick its size, pulling down 18-19mpg highway with the 4spd granny-box seemed pretty awesome. Still blew oil, indicating blowby and i still had to spend just about every weekend cleaning the engine off. I replace the pcv valve and still had blowbly. Now, today when i popped the hood and watched the engine run with the pcv hose disconnected, i got virtually no blowby. Maybe a real light light, almost impossible to see grey puff when i revved the engine. (Note the engine was cold, i just did some choke adjustments, got tired of those hard starts.)

What could have caused it to suddenly stop having blow-by? The only things that come to mind is 1)Dangerously low of oil. Or 2)Rings finally seated, as in the truck had been sitting for a long period of time prior to my purchasing it. I'm thinking #2, because i know the crankcase is full of oil, the pcv system is clear, so there isn't really much else i could point the finger at.

Anybody have any clues? Is this odd, or should i just forget about it?

 

Valve Seals could have been the cause as well.

 

Probably had stuck rings from sitting.

 

Hook the pcv back up and see if the blowby returns.

 

I guess i muddied the waters a bit. The PCV connection itself is still connected, the breather hose that goes to the air filter is what i disconnected. I'm still not getting blowby, and it seems to be running great.

I think myself it was stuck rings, or valves maybe from sitting, but who knows.