The Magic Disappearing Oil

You folks should know me by now, so I hope you will help solve my dilemma.

I have a 2001 Chevy Prizm - a Toyota Corolla clone. It has about 50K miles and uses oil at the rate of about 1 quart every couple hundred miles. You’d think if the oil was being burned, it would leave a trail of smoke behind the car - or at least, the rear of the car would be covered with oil. Or if there was a leak, the underside of the car would be covered with it.

Nope, neither of those cases. No drips in the driveway, the underside is clean, no smoke. The only trace is that around the exhaust is a small amount of oily dirt - but it seems only slightly excessive - certainly not in proportion to the amount I am using.

Any ideas where the oil is going?

When did you last replace the PCV valve?

If there is no evidence of oil on the undercarriage, I’d figure you’re burning it.

The trick is figuring out why.

One question though.
A 13 year old car with only 50K miles…had to believe. That’s less than 4000 miles a year.

Are you sure the mileage was not tampered with before you purchased it.


VDCDriver said: “When did you last replace the PCV valve?”

Like, never. Are you suggesting that the oil is bypassing the combustion chamber and going directly into the exhaust? Shouldn’t the catalytic converter burn it? So shouldn’t there be smoke?

Yosemite said: “…A 13 year old car with only 50K miles…hard to believe. That’s less than 4000 miles a year…”

I inherited it from my father-in-law, who was 90 when he died. He hardly drove it - so yes, I am sure about the mileage - and I am sure the short trips he took with it had something to do with why I am losing oil. The question I am trying to figure out is where to look.

“Shouldn’t the catalytic converter burn it? So shouldn’t there be smoke?”

The catalytic converter would actually “eat” the smoke–until the point when it is ruined by the accumulation of oil residue. In light of the very low cost of a PCV valve (less than $5.00, IIRC), I would suggest replacing it and the hose that it is attached to. Even if it doesn’t resolve the problem, this is an extremely cheap experiment for you to try.

I have an '03 Camry with similar mileage and no issues. When my Dad was still alive, he had a few cars that would see even less usage than your inherited car and primarily short hops. They rotted out prematurely but weren’t oil burners.

What about the maintenance history, know anything about oil changes?

I’d pull the PCV if it has one and check for positive pressure out the crankcase port. Regardless, change the valve.

Then, based on maintenance, would suspect coked rings. How long have you had it? Problem since day one? It may resurrect itself if subjected to “normal” usage but i’d be inclined to try a solution to clean the rings proactively.

@TwinTurbo Yes, That driving pattern often results in stuck rings and oil consumption. There are a number of additives to loosen up rings, and I would try that first. The PCV valve should be replaced as well. A good deal of fast highway driving will also loosen up the engine.

With this low mileage the converter will not likely be plugged, but if oil usage continues it soon will be.

I’m gonna go with stuck oil rings on this one, because of the car’s history.

VDC suggested the PCV valve because if that’s stuck closed it’ll allow excess pressure to build up on the crankcase. This can force oil past tired crank seals (since that only happens when the engine is running, it can be misleading to use a driveway puddle or lack thereof as an indicator), and it can even cause oil to be pushed to the space under the valvecover, where it can be ingested (even a closed PCV valve allows some passage) and burned.

The cat converter doesn’t actually burn smoke. The oil in the smoke coats the platinum-palladium coating on the converter’s ceramic honeycomb (the “catalyst”) until it can no longer contact the NO2 molecules and strip them of their oxygen atoms… until it can no longer do its job. At that point the converter becomes ruined.

I think trying the additives is a great idea in this situation. Let us know how you make out.

Join the club. This is a common problem with the Prizm/Corolla.

The problem is likely stuck oil control rings as mountainbike said. I would try a “miracle elixir” engine treatment such as Seafoam or Kreen. It’s inexpensive, can’t hurt, might help.

If the oil control rings are badly stuck, the only real fix is to disassemble the engine and unstick the rings manually. In which case it’s cheaper just to keep adding oil as needed.

But a few cans of Seafoam or Kreen are cheap and may help.

Well, it has to be going somewhere. That fact is certain. I concur with the PCV thing, at least checking you get suction through it at idle, and it rattles. I usually also remove the oil filler cap and put a piece of paper over it the valve cover opening, see if it holds fast, to make sure there’s suction there too (with the PCV etc installed). You’d think stuck oil control rings would result in some blue smoke clouds out the tailpipe. But I guess if the oil loss rate isn’t too much, the cat can eliminate the visible effects. Some manufacturers say one quart oil in 500 miles is within normal, and that rate of oil loss out the tailpipe usually doesn’t result in much smoke. The rate of oil loss you are reporting isn’t much more than that.

If it’s not leaking then it’s going past the piston rings. The reason for no smoke is because the burned oil is caking up on the converter substrate. The hot converter is constantly cooking the coked oil into microscopic soot which is then expelled out the tailpipe instead of smoke.
Stick a rag up the tailpipe and see if it comes out sooty black.

Thanks everyone. Here’s what I got out of this thread:

It is very very likely that the oil is being burned, but the reason there is no smoke is because the cat is collecting it - which also means eventually the cat will get clogged.

The fix is to use a magic elixir - something with the word “Miracle” in the name (like Tommy used to say) - or better yet, Seafoam or Kreen.

The more drastic (and expensive) fix would be to disassemble the engine and manually clean.

Oh, and change the PVC valve.

Yep, that’s about it. Hopefully, if the rings are gummed up, this will free them. Once the oil consumption is reduced, the cat may be able to clean itself if it is not too far gone.

Another option short of engine teardown is a piston soak.
Pull the spark plugs and fill the chambers with a suitable solvent.
Let sit a few hours, topping off the solvent. Wiggle the crank back and fourth a few times.
Disable the ignition, throw a rag over the plug holes and crank the engine to blow out the remaining solvent.
Pour in a little oil to re-lube the cylinders and replace the plugs.
Start it up. Let it idle. There will be some smoke at first.

Let me throw in another possibility. My son bought a truck back in 2000 that did this “disappearing oil” trick. When he told me that he had to add 4 or 5 quarts in just a couple of days…I immediately went to his house to investigate. The truck was a '93 Chevy C1500 with a 5.7 engine. I listened to his story again and was told there was no smoke and no leaks. I then told him to remove both valve covers. When he did…about half of the gallon or so oil he had added flowed out of the top of the engine. When he removed the other valve cover…the other half flowed out. The problem was that the oil drain holes in the head were almost completely stopped up. We cleaned up the engine and cleaned out the oil drain holes using a shop vac. We then changed the oil and filter. The truck never had a problem with oil consumption after that. The engine looked brand new on the outside but internally…the engine looked like the depths of h e double hockey sticks.


Changed the PCV valve, and added Seafoam to the oil per the instructions on the can. One thing of note.

Not only is there a breather connected via the PCV valve from the valve cover to the throttle body (after the throttle plate), but there is another breather (unrestricted) also between the valve cover and the throttle body, but BEFORE the throttle plate. Both hoses were dry.

The plan at this point is to change the oil at 1K miles, do the Seamfoam treatment again, another 1K oil change, and see where we are. I’ll post back in a couple of months if there is a change in oil consumption.

I would use Rotella synthetic. It has high detergent levels.

“Not only is there a breather connected via the PCV valve from the valve cover to the throttle body (after the throttle plate), but there is another breather (unrestricted) also between the valve cover and the throttle body, but BEFORE the throttle plate.”

This is the typical PCV system.
Crankcase/valve cover fumes are drawn through the PCV valve by manifold vacuum; and fresh filtered air is drawn into the valve cover to replace what was drawn out.

Clean hoses and PCV valve means there’s little or no blowby to throw things out of balance.
So I think the top rings are OK, but the oil control rings are gunked.

Time for an update.

I have put 3K more miles on. Changed oil every 1K and added Seafoam to the oil at every change.

Result? No difference. It still burns oil at the rate of a quart every 500 miles or so. It might be faster as the change interval wasn’t exactly every 1,000 miles and my checking the level was always at an even value and I was pouring from a 5 gallon bottle. I’ll just have to adjust the way I do things so I check the oil more frequently.

Nevertheless, thanks to all for the help.

Unfortunately beyond the aura of Toyota this engine has problems.

I would not waste any money on synthetic oil on this car, just buy the cheapest modern oil you can find and pour away.

The trunk accessory will be the case of oil for this one, my ski buddy has the same thing in the back of her 2001 Corolla she laughs at.