blowby?

[shortbed70]

My trucks 350 doesn't smoke on startup or idleing but when you accelerate on the highway or rev it it blows blue. not much but enough. I've been told it could be blowby but also have been told the valve guides can be worn. Can somebody tell me what could be causing this.

[Longhorn Man]

Normally, the first signs of blow by would be in the PVC system. Pull your PVC valve, and look in it, and it's hose, for signs of oil. A little is ok. Not really ok, but acceptable. Alot...well, then you may have found your problem.
Do a compression check recording your numbers, then do it again, but squirt some oil in each cylinder. If the numbers shoot up quite a bit, then your looking at worn rings/cylinders.

[da-burb]

It is you piston rings. Either just worn out or stuck. It happens when you accelerate because that is when cylinder pressures are the highest and combustion gasses are slipping past the rings and cooking the oil below into the blue haze you see exiting your tail pipe. I have a 351W that does this extremely well.

If it were worn valve guides you would see the smoke when you let off the gas or down shift while coasting. This is from engine vacuum pulling oil past worn valve guides. The poof of smoke on start up is another sign.

A simple test for blow by on your engine is to remove the PCV valve from your valve cover. Then remove the other vent tube from the other valve cover. Now rev your engine and you will see the smoke pour out those 2 openings in your valve covers if the blow by is bad.