excessive oil use

The symptom for leaking valve stem seals is blue smoke on startup after sitting overnight, not necessarily on hard acceleration.

If you see blue smoke when accelerating hard, that can be an oil control ring problem.

White smoke when accelerating hard could be a head gasket problem, and black smoke is a fuel mixture problem (would set a check engine light).

When you checked cylinder compression, did you do "dry" and "wet" compression measurements?

1 quart of oil per 1,000 miles is on the very high side of normal oil consumption.

What viscosity and grade of oil are you using? How often was the oil changed?

Given the symptoms you cite, I'd go with the valve stems.

Leaking valve stems smoke at startup because the oil pools on top of the pistons. The OP mentioned that it does not smoke at startup.

I read that too, and missed the connection.

I was thinking that oil would flow down the valve stems while the motor was running, and result in high oil consumption. The oil rings would certainly play a huge role here though, especially if the compression checked out good -- which I gotta wonder about.

That could happen but you would still have clouds of smoke at startup.

The oil rings would certainly

The OP didn't mention dry & wet compression results so there isn't conclusive evidence.

I forgot to mention to check the PCV valve and make sure it's not stuck.

Can you explain the role of the PCV valve in oil consumption? I think I know the answer, but not well enough to explain. I suspect there are people here that do not know what the connection is, and how the PCV valve enters into the discussion.

My thoughts are that if the PCV is plugged, then under high vacuum, decelleration, oil can be forcibly sucked past the otherwise reasonably working rings. That is, even where the rings are working, but worn, the oil can be pulled past them if the PCV is clogged. I assume that if the rings are working at 100%, then the PCV wouldn't be all that improtant here, and plays a more signfiicant role on an older engine. I'm not sure that is what happens though.

"

Dry compression 195, 190, 195, 200 Wet compression all were 220 New PCV valve, took off valve cover - clean as a whistle, no blockage in hoses

Blowby is the product of combustion which sneaks past the piston rings. An engine with worn rings will have a lot of blowby, an engine in good condition will have only a little, but all engines have some.

That blowby has to go somewhere. The normal route is through the Positive Crankcase Ventilation (PCV) valve. If the PCV valve is plugged the blowby causes engine seals to fail. Oily vapor exits the engine at the rear main seal, front main seal, camshaft seal(s), even the valve cover gasket.

In other words, a plugged PCV valve will cause oil consumption, but as a leak rather than as burned oil.

Daniel B. Martin

Sounds like rings and PCV valve are OK.

Here is a well-written article on oil consumption.

I can't answer for every engine, but I can answer for the 2T-C and 3K-C series. If the PCV valve clogs, the engine starts sucking oil right into the carberettor and burns it. I suspect something similar with the 7Y engine I have now, even though it hasn't a carberettor.

Charles of Kankakee

I guess I didn't actually answer Jeff's question regarding how a clogged PVC valve could cause high oil consusmsption; I just posted the link.

Oil is not sucked past rings. Every engine produces some blowby - gases from the combustion chamber that seep into the crankcase. Prior to the installation of emission controls, those gases were just vented into the atmosphere. The PCV valve routes those gases to the intake manifold to be re-burned.

The amount of crankcase venting is inverse to manifold vacuum. When vacuum is high (engine idling) the PCV valve is closed or almost closed. When vacuum is low (high RPM) then the PVC is open so more gas is vented into the intake manifold.

If the PCV valve was stuck in the open position at idle, the high vacuum could start sucking oil mist out of the crankcase and burning it.

I assume that if the

Sure...remember the old engines?, there was no pvc valve, the crankcase was vented overboard. This wasn't too environmentally friendly so they invented the pvc to ventilate the CC and yet not spew contaminates o'board.

Obviously you are a rookie.

ALL .... Positive Crankcase Ventilation systems incorporate BOTH a variable flow air valve in a path between the crankcase (or valve cover) and the intake manifold 'after' the throttle and ... a breather hose which nearly always connects the valve cover to the air intake between the air filter housing and the throttle.

ANYTIME the variable flow air valve is overcome by crankcase blowby gasses or if this valve becomes obstructed, air flow through the breather hose is reversed. That is to say all blowby will now enter the intake track at a point between the air filter housing and the throttle.

Oil control rings are always "working". If you doubt this, remove them from any 4 cycle engine and then fire it up. Furthermore, oil control rings do not seal compression from the crankcase. It is when the compression rings are failing to contain combustion chamber pressures that "Blow-by" occurs ... hence the term.

-Philip

I'm not that much of a rookie. ;-)

I'm still not getting how the PCV can cause an engine to burn a quart of oil in 1000 miles. My first three cars didn't have PCV valves, and they also didn't burn oil at that rate, so something else has to be the problem. Or, this can be the problem, but it hasn't been explained well yet.

I am not disputing what the PCV does, I know what it does. I'm asking how it contributes to the oil consumption rates that the OP is complaining of.

Canadian Driver? Well, that blows the credibility ...

Good explanation. The OP didn't discuss his habits of hitting Red Line, and if all else is fine, this in itself could be the trouble.

"J Strickland" wrote in message news: snipped-for-privacy@ez2.net...

What sort of cars did you have that didn't have a PCV valve? As far as I know all cars sold in the US since the early sixties have been required to have PCV system of some sort. Older vehicles used a road draft tube and a crankcase breather (either directly into the crankcase or into the valve cover). As the car moves forward, air is sucked out of the road draft tube (really just an open pipe down into the air stream) and fresh air is drawn in through the breather.

As Phillip described, the Positive Crankcase Ventilation systems (as opposed to the passive road draft tube system) uses engine manifold vacuum to suck vapors from the crankcase. The amount of gas sucked from the crankcase has to be metered to prevent the crankcase vapors from adversely affecting the engine performance. The crankcase vapors are sucked into the intake tract downstream from the throttle. The PCV valve includes a metering orifice and a one way valve. The one way valve prevent flow from the intake manifold into the crankcase (and the possibility that a backfire might ignite the gases in the crankcase). The air sucked from the crankcase must be replaced with fresh air. Usually the intake for the PCV system is in the intake tract after the air filter (some cars use an PCV intake before the air filter and give it a separate small filter). Two bad things can happen if the PCV fails. If the PCV orifice becomes clogged, or the one way valve is stuck shut, pressure will build in the crankcase and this can force vapors and oil into the intake tract through the PCV system air intake. This will show up as a large amount of oily residue in the intake tract. If the PCV intake is small or clogged along with a clogged PCV valve, pressure can build up in the crankcase and force oil out through seals and gaskets. A worn engine can dump so much blow-by into the crankcase that it can overwhelm the PCV system and force oil past the seals and gaskets as well.

Ed

My first car WAS from the early '60s, and the cars we had at home were older. ;-)

But even with the breather, the oil consumption didn't change, just what was emitted into the atmosphere changed.

Now that part makes sense.

But, it seems that this kind of failure would manifest itself in puddles of oil on the garage floor. The question I am trying to get squared away is how the PCV can cause oil consumption rates of a quart per 1000 miles. This was the OP's complaint. I can not square the complaint with the remedy of fixing the PCV.

We (I) have a good understanding of what the system does when it works right, the question is, how does the malfunctioning system cause so much oil to be consumed? There has to be other problems in the engine that cause the PCV failure to have such an impact.

I thought that the link I posted gave a pretty good explanation of where the oil goes if the PCV valve malfunctions. I thought that Philip and Ed also gave good explanations of where the oil goes.

The reason that the crankcase is ventilated is so that blowby gases have a place to go instead of trying to pressurize the crankcase. In the olden days, it was ventilated to the atmosphere.

Today, the vent goes to the intake manifold. In other words, there is a physical passage for blowby gases to travel from the crankcase to the intake manifold. If the PCV Valve is stuck, oil vapor could get sucked through that passage and get burned instead of just blowby gases.

What brand and grade of oil are you using and how often have you changed it?