hey yall just lookin for some input on what to try next i have a 93 f250 hd 4x4 351 got it for free runs drives shifts 4x4 works good just getting some excessive blowby checked my pcv valve it still rattles good no clogged hoses but noticed when i checked the hose going from oil fill to airbox it was blowin smoke it was smoke not steam for sure. gana do a compression check on it soon as i can it only has 125,000 miles on it so i would be a little shocked if it was bad rings plugs all looked good no fouling all normal wear. thinkin maybe the drain down holes ( im sure theres a propper name for em but i dont know it ) in the heads may be clogged and possible causin oil to pool and run back through valves dont really know any ideas suggestions would be greatly appreciated thanks yall.

 

is it enough to blacken your hand if you hold it by the hose? rings wouldnt cause this, only blue smoke from exhaust. mine does this a little, i would just plug the hose. i would even worry about it, the point of that hose it to suck oil fumes form thevalve covers.

 

i know the purpose of the pcv system but this isnt normal little bit of vapor coming out the hose its full blown blue smoke hittin a lick with the motor its just an old huntin and fishin truck but i dont want to cause anymore damage than is needed unless it involves killin a swamp moose or catchin a big fish. im gana do a comp. check when i get back from ky this weekend and see what it shows, if its good depending on what the readings say fix what is wrong. hopefully nothin major thanks for the input though.

 

First I would check your breather filter in the left valve cover to make sure it’s not plugged and air can travel freely.

Next remove the PVC valve and hose to the intake manifold. The valve should rattle freely and there shouldn’t be any oil accumulation inside the hose. Blow in the end of the hose to see if the valve seals tight and blow in the valve to make sure it flow freely.


Then, go for a drive to get the engine hot. With the engine running, remove the PVC valve and make sure there is a vacuum sucking through it.
place your thumb over the valve to seal it and open the throttle to bring the RPM up to 2-3k. You’re looking for oil vapor coming out of the valve cover. With good piston rings, there should be very little if any, if bad rings there could be a lot of air movement coming out the hole.

Next, buy, borrow or rent a vacuum gauge and connect it up and start your engine. Steady low reading could be bad rings, low and fluctuating could be an intake manifold leak. Below is a good YouTube video.


Blue smoke on startup is usually bad valve stem seals or plugged oil return holes in the heads. Blue smoke on acceleration usually is piston rings. If pulling the plugs and it’s only 1 or 2 plugs show signs of oil fouling, it could be something else.

I guess what I’m getting at, do as much diagnostic before you go down the rabbit hole of tearing things apart. Pulling and replacing the intake and valve covers is not the simplest job on a 89’, there is 20 pounds of crap to pull off before you even get to the manifold and you will spend all weekend on it.
And if you find more bad once the manifold is off, are you ready at that time for a $4k engine rebuild and having the truck dead in that spot for months?