I have an 01 Chevy 3500 and have a lot of blowby. My mechanic says that I have 3 cylinders that are ready to misfire, and that i have oil rings that are bad. Could that be the reason for the excess blowby?

loss of compression piston rings --valves --cam worn--lifter failing weak or damaged valve springs these would also cause misfire

You describe the situation as a heavy blowby. In the usually accepted meaning of the term blowby relating to an engine, means piston blowby and is recognised by a large amount of whitish vapour being expelled through the crankcase breather, dipstick tube and the oil filler cap if removed. This usually indicates the excessive wear of cylinder bores, pistons and piston rings that are no longer capable of sealing and allow combustion gas to blowby.

If the vapour puffs in sympathy with the engine speed it suggests stuck or broken piston rings confined to a single cylinder or a damaged piston.

It is difficult to understand how this would happen with a newly overhauled engine that surely must have been rebored and had new pistons fitted in order to qualify as overhauled. I can possibly advise you further if you post details of the overhaul in the comments section.

Not unrelated but perhaps surplus information just now - new cast iron piston rings take 500 miles to bed in to new properly honed bores while steel rings take 1000 miles. It is important to complete those miles with the engine filled with a base or low grade engine oil or proper running-in oil. Filling a newly overhauled engine with a modern high-spec oil can mean the piston rings will never bed in and forever afterwards the engine ios likely to smoke and consume a lot of oil.

Could be a plugged PCV (positive crankcase ventilator) valve. Cheap and easy to replace.

Could also be lots of other things such as excessive blowby caused by bad piston rings or a cracked piston or damaged cylinder head allowing compression in one cylinder to leak into an adjoining cylinder.

In any case, don't continue driving until you address this. You could turn a minor problem into the need for a new engine.

The carbon suggests that oil is finding its way into that cylinder and oiling/carbonising the plug.

The mechanic changed the rings so it's doubtful that the oil is finding its way into the cylinder, past the rings. The only other thing I can think of is that the valve stem guide is worn (this would allow oil down into the cylinder) or the valve stem seal is perished/worn.

The photos below are generic images. They are NOT of your car:




A valve in the valve guide. A worn guide can allow the valve stem to 'rock' and permit oil to trickle down the valve stem into the cylinder.



The seal itself - rubberised.

There's many different types of seal. General image below just for illustration purposes:



Bluish smoke indicates that oil is being burnt in a cylinder. To be honest, worn valve guides/worn seals are quite common. You say your car is misfiring? That would indicate quite a lot of oil is fouling the plug. In most cases there would be no misfire after just 3 days. The exhaust would cough out bluish smoke at start up and maybe on the over-run, when going downhill.

A short term measure is to try a can of valve seal additive to see if the problem temporarily goes away. Repair is the best option though.



Try a can of valve seal? It's worth a shot..

have mechanic run compression test. might need rings or valve job

A bad injector, piston ring blowby or a head gasket/coolant problem can also cause a cylinder to misfire.

Compare the color of that plug to one from another cylinder. If it is wet and gassy you have too much gas or not enough spark. If it is black and oily you have a piston ring problem. If it is sweet smelling, watery wet or white foamy you have a head or head gasket problem, if it is white then you have a too lean condition (plugged or faulty fuel injector).

There should be no built up fuel or oil in cylinder. The fuel will be burned off immediately, and there should have been very little unless you have a leaking injector. The only way oil will enter the cylinder is if you have a mechanical failure like worn rings or leaking valve seals.If after replacing the plugs and wires did not correct all or the skip after the first start up and road test then you have another issue causing the skip

IF YOU GOT CYLINDER MISFIRE.OR OPEN FUEL INJECTOR.THAT WILL CAUSE THE PCM TO ENRICHEN FUEL MIXTURE.TO ADJUST TO DEAD CYLINDER.WHICH ACT AS A LARGE VACUUM LEAK.THATS WHY YOUR EXHAUST TAIL PIPES HAS A RAW FUEL SMELL AND WHITE SMOKES.

I think you could be right. Leaking valves could create this same problem as well.

if you have blowby you have oil getting past your rings.or through a valve which can also be causing the misfire..the sensors you need to have it dianosed with a computer to see if there are any error codes