excessive oil use

No 'bingo.' A pressurized crankcase cannot force oil out the bearings. Such is the end result of the oil pump pressurizing oil to the oil delivery galleries and THRU all bearings.

-philip

Total rubbish.

The reason Detroit moved to the lighter grade 10w-30 and then 5w-30 has been for fuel economy. They're looking for every last 10th of an MPG the can get. Why do you think 5w-20 is now standard fill in some cases? Hmmm? It's all about fuel economy.

snip

There does NOT need to be any blowby whatsoever (were that possible) for there to be considerable oil consumption.

The compression rings block combustion pressure from entering the crankcase. The oil rings are not capable of serving this function. Look and compare the difference in construction.

-Philip

ALL crankcases are vented to the atmosphere. The "atmosphere" is defined as any point in the engine intake air delivery stream between the air filter housing and the throttle.

snip

Not universally true. Some cylinder head designs tend to pool oil around the valve guides while other designs facilitate oil quickly falling away from the valve guides. In the first mentioned design, a marginal guide seal would permit some oil to pass it shortly after shutting down the engine.

Half true. A dry/wet compression test comparison determines ONLY compression ring integrity. Remember, oil rings do not seal against compression that leaked past the two compression rings.

A Positive Crankcase Ventilation valve NEVER "closes" completely at idle. At idle and when coasting (high manifold vacuum), manifold vacuum positions the PCV valve at its lowest flow position. At low manifold vacuum, the pintle valve spring pushes the valve to a high flow position. Keep in mind that at higher engine loads (low manifold vacuum), there is much less pressure differential between the crankcase and the intake manifold. So ... whatever crankcase pressure generated that cannot push through the PCV valve now exits out the crankcase breather hose (intake air stream between air filter housing and the throttle).

-Philip

I guess "ambient air" would have been a more accurate term.

I've spent so much time on this stupid thread that I forgot what kind of car was being discussed. I thought it was a Camry, which is notorious for smoky startup with bad valve guide seals.

Oops, I know better and still missed that error.

Yup, saying a PCV valve is closed is like saying the throttle is closed...

OK, where do you think the oil is going?

Excuse me, but I thought it was about tighter mechanical tolerance and in cold places, better ability to flow when the engine is cold, that is using 5W30.

Nope. My Chevy truck recommended 5 W 30 so they could get just a little more MPG out of it for the CAFE. My Toyota recommends 10W30 unless it's going to get cold. A couple years later with the same engine, they went to recommending 5W30 with no change in the engine.

Charles of Kankakee

Excuse me ... I suggest you crack open some Motors Repair manuals and compare engine for engine the piston skirt clearances and crankshaft clearances on just about any engine you care to that has been in production for a decade or two. There has been no such SIGNIFICANT reduction in these tolerances. (significant is more than 0.0007")

Regarding 10w-30 vs. 5w-30, you will find a very small real world difference between the two until ambient temperatures drop below 5 degrees. Even so, how long do you think it takes for engine oil to warm up to say 30 degrees .... at which point the two weights are about the same? 5 minutes? Big deal.

-Philip

I think it's time for the OP to repost what he HAS done in the way of diagnostics and identify what symptoms are present. WAS this an old Camry? LOL

I just stumbed across this thread and am too lazy to trace it back to its origins.

-Philip

You have to be a youngster that was not around back then because it was serious problems for GM with some engines in the 80?s. They had a LOT of problems with sticking rings in some engines and stopped recommanding 10w40 period. 10w40 has a LOT of VI in it which can and will cook out and gum up rings when conditions are right. (10w30 straight 30 or even 15w40 Dino oil is okay but 10w40 is a no no in GM?s book and not because of MPG ). This was before the 5w30 thing and that came about because they decised that 5w30 gave better lubication to camshaft for the first 30 seconds or so on a cold start below zero, the MPG gain was a after thought. Just because you do not know or understand does not make the facts rubbish. I have been working on cars since the 60?s and I have seen a lot of things that you do not read in the forums.

snipped the rest of your post.

Age 70 and doing well. I was repairing cars and trucks professionally until '87. The "serious" problems you allude to are matters you have not verified. There were NO 'sticking rings' due to anything but failure to perform appropriate oil changes for conditions coupled with abrasive fuel additives of the day. There was concern regarding ash content and the hard carbon accumulations on the piston crown affecting emissions. These were the days of SF oils. I attended a series of technical seminars at Delco in Burbank back then. I recall the 'findings' and concerns GM had about motor oils at that time.

-Philip

I'm confused.

PCV being plugged, in and of itself can not cause the oil consumption rates that the OP asked about. If the PCV is a contributor, by all accounts it will lead to external leaking of oil, not burning of oil. I am stuck on the burning of the oil because the OP didn't way it was leaking.

Please explain how the PCV -- Ray brought this up, and I'm not getting it -- can cause oil to blow through a motor at the rate of a quart every 1000 miles. I am saying that if there is oil going through the motor that fast, it has to be issues beyond the PCV. Sure, the PCV might be clogged, but by itself it isn't the problem.

If the PCV was clogged, AND there were problems with the rings, compression and or oil, then we could see the consumption rates that the OP is siting, and even if the PCV was working well, we could have the consumption rates if the rings were toast.

My specific question is, if the rings are in good shape and there is no external leaking, can a clogged PCV cause the oil consumption rates we are talking about?

My personal thought is that the motor is being driven too hard -- it hits red line alot -- and then the lead foot is lifted with the motor spinning its guts out, the resulting vacuum on the motor is sucking oil past the rings and the valve stems. I agree that it's a good idea to replace the PCV valve, but if he doesn't change his habit of visiting red line, he'll continue to buy oil by the case and use it. The good news is, he can probably forget about oil changes because he is pouring in the oil faster than it wears out.

The OP has a 2000 Corolla.

Where is the oil going?

It's a 2000 Corolla with 82k miles. The OP says there is oil on the back of the car, and he is pretty sure it comes out of the tail pipe. I think the oil is blowing past the valve seals on decelleration, or being sucked past the rings, or a combination of the two.

We got on the PCV because Ray offered that this was the problem. It might be a contributor to the problem, but its not The Problem.

You pour a quart in every 1000 miles, then change it every 3000 miles? That's 6 quarts of oil every 3000 miles, or a quart per 500 miles. That seems like a lot to me. Are you sure it is burning and not draining?

For what it's worth, I'm with Phil on this one. 10/30 and 5/30 are equivelents until the ambient temps fall somewhere below freezing. I don't know the precise temp, but the idea is that thin oil -- the 5- an dthe

Jeff says its a 2000 Corolla, I think it had 50 or 80 k miles. The OP says the inside of the tailpipe is black, there is a black oily residue on the bumper near the tailpipe. Dry and wet compression was OK, recently had the PCV valve changed, no visible oil leaks. No smoke on startup.

Oil changes every 3k miles with Valvoline 10W-40, uses 1 quart/1,000 miles.

Jeff,

You don't have to take my word for it. Check a repair manual on possible causes of excessive oil consumption. A clogged PCV by itself could be the problem.

Yes. (see above)

The "vacuum on the motor" will not suck oil past the rings and valve stems, redline or not.

That's true!

That depends. I can make a good case to you where an obstructed PCV valve -could- bring about one quart per thousand miles consumption.

NO NO NO. An obstructed PCV valve does NOT have to lead to external oil leaks. You have got to get it through your head that there is a substantial diameter crankcase BREATHER hose (aka crankcase air inlet hose) in EVERY Positive Crankcase Ventilation system. This parallel path becomes an alternate exiting path for crankcase blow-by gases when the PCV is clogged or overwhelmed.

Do you mean to ask how a normally functioning or an clogged PCV might allow

Look ... ANYTIME the volume of blow-by exceeds the PCV's flow rate, the excess will be vented out the crankcase breather hose. THIS is why you often see some oil residue around the crankcase breather where it enters the air stream between the air filter and the throttle.

Yes. You cannot put the whole blame on the PCV without considering the capacity of the crankcase breather path. The two work together. If or when the crankcase becomes pressurized, oil will be pushed to all areas of lower pressure. That means intake manifold vacuum and atmosphere (valve stem seals and external oil seals respectively).

FORGET this 'sucking past the rings" s*it. Look ... do a compression test with the throttle completely closed. What kind of readings do you get?

So long as the PCV pintle moves freely when you poke it with a screwdriver, there's really no need to replace it. DO be sure to get the right one (cfm size) as the aftermarket units are not always the same flow rate as OEM.

-Philip