Engine Blow-By question?

Question

I was wondering if blow-by is caused by having bad piston rings or if a bad valve guide could be the problem?. I was looking at a 94 saturn Sc2 for my sister. The engine had such bad blow by when I took off the oil cap with the engine running to see how good the oil pressure was the oil cap poped out of the valve cover hit the hood and landed in my hand what could cause such bad blow by?. the enigne seemed to be running fine. After the oil cap pop out, the top of the engine sounded like an old piston air compressor. I didn't buy this car but I just was curious as to what would make the engine do this?.

engines today do not operate on positive crank case pressures. I have never had ANY car do that. My 93 Grand prix doesn't do it my dads 06 Crysler Town and Country does not do this my sisters 96 Mazda doesn't do it. So MUSTANG you are wrong.

All crank case emissons are sent through the PCV system and into the intake plenum to be burned. Even in old cars the crank case pressures are no wear neer what this car had.

All crank case emissons are sent through the PCV system and into the intake plenum to be burned. Even in old cars the crank case pressures are no wear neer what this car had.

All crank case emissons are sent through the PCV system and into the intake plenum to be burned. Even in old cars the crank case pressures are no wear neer what this car had.

Answer 1

The rings are likely shot. They're leaking so badly (blow by) that you are actually hearing the combustion pulses as they pressurize the crankcase (and find relief through the oil filler when you remove the cap as you did).

Worn valve guides won't do it - this is an active, dynamic discharge of combustion gases by the rings and cylinder walls while the engine is running. It may run just "fine" as all cylinders are likely fairly evenly worn and there is little imbalance therefore between cylinders. Also, just because there is a loss of compression there is still enough dynamic compression and combustion pressure holding to deliver sufficient power - for now. It will get worse as such worn rings and diminished wetting surface on the cylinder ways results in more rapid wear (the minute cross-hatching wears smooth so there is inadequate channeling to carry an adequate and unifor oil film - so wear increases).

Not buying this car is wise - somebody likely didn't keep fresh oil and air and oil filters in it, or drove the crap out of it, or both.

Answer 2

Nothing was wrong, most likely. Back in the old days engines were vented with air coming in the oil cap and vented out a road draft tube. Engines today, due to emissions requirements, are not vented but run at a positive pressure. They aren't meant to be run with the oil cap or the gas cap removed.

Answer 3

Blow By is caused by worn rings. On the compression stroke some of the pressure gets by the rings and enters the crankcase. thats what blows seals and gaskets that causes an engine to leak

Answer 4

Could be a plugged PCV valve not allowing the blow by to escape the crankcase.

Answer 5

If the vent system is plugged up (PCV valve and hose) that will do it. If the rings were that bad it would foul plugs and run like crap

Answer 6

blow by is caused by maybe a broken ring or seal leakage,

Answer 7

pissed n Broke (piston broke),or blocked fluffer valve,been thrashed ,walk away