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Excess oil consumption & catalytic converter

A few months ago I got a real good deal on a 2002 Toyota Sienna van trade-in in Minneapolis with 155k on it. I drove it 1700 miles home to Seattle, and along the way I needed to put in 12, yes 12, quarts of 5W-30 oil. (average: 1 qt./140 miles) But there was no smoke coming from the tailpipe at all, even at first start-up in the morning. I also had it put up on a hoist, and no oil was leaking out.

When I got home I had the valve cover removed at a Toyota dealership to check for the infamous oil/sludge problem. There was none, but all the spark plugs were oil fouled but still functioning. When the dealership checked their national maintenance system, they discovered this van was extremely well maintained with all of the oil changes done at a dealership and on time. And all the 30/60/90k checks were also done on time.

They were at a loss to explain where all of the oil was going, and especially surprised there was no blue smoke coming from the tailpipe. And the check engine light never came on the entire trip.

So I took it to a repair shop I’ve used before, and the manager was also at a loss to explain it. But a mechanic overheard us talking and came over. He reached in behind the engine, pulled out the PCV valve and said, “This is an after-market PCV valve, and it’s clicking when I shake it, but it doesn’t sound just right.” It turns out he was a Toyota master mechanic. I wasn’t even charged for his advice.

I purchased a new Toyota PCV valve for $10, put it in and went and had the van emission tested. It passed with no problem. I brought the oil level up to full and drove it for a few hundred miles. It used no oil at all.

In the first 1000 miles after putting in the new PCV valve, it has used only 1/4 of a quart of oil.

But here is my question. The previous owner had to replace the catalytic converter 5000 miles ago, because the check engine light kept coming on and the code indicated that was the problem. In your opinion, do you think that all of this oil that has gone through the engine will cause a premature replacement of this fairly new catalytic converter?


It may.

The most functional part of a catalytic converter is a ceramic substrate honeycomb coated with platinum-palladium, the actual catalyst. When molecules of bonded nitrogen and oxygen come in contact with the hot cataytic surfaces, the bond betwee the nitrogen and oxygen is weakened and the molecules seperate into nitrogen and oxygen. That provides the oxygen necessary for the “second burn”, wherein carbon monoxide molecules can pick up an oxygen atom and become carbon dioxide molecules. The nitrogen is considered harmless by itself.

If the catalytic surface coating is coated with residue of burning oil (carbon) than the NOx molecules cannot come in contact wil the catalyst and none of this stuff can happen.

However, since it passed emissions testing and you have no CEL light, you’re fine. Don’t fix it 'til it’s broke.

I thought that was a very clear explanation. Thank you . . .

You’re welcome.


The converter will have suffered some caking on the honeycomb inside, which is normal with oil consumption.
However, with only 5k miles on a new converter and the problem pretty much cured odds are that most of what was caked in there has burnt off. It will never go away completely.
The only way of knowing for sure is by disassembling the converter, but I agree that if the car runs fine with no CEL you should not worry about it.

The great part is that the lowly PCV valve took care of the problem. The problem in this case was that the PCV was not completely frozen but was simply gunked up. This would explain the not sounding right part the mechanic referred to.
They should sound like a rock in a tin can but if they have a somewhat subdued or muffled sound this means the PCV is gunked up.

Thank you. I appreciate your answer . . .

A plugged or defective PCV can cause problems, usually sludging or oil LEAKS. Sometimes considerable oil is forced back into the air-filter box and makes a mess. But I’ve never seen one cause oil consumption like you experienced…Anything is possible I guess…perhaps the crankcase air intake is completely unbaffled so if air flow is reversed, a lot of oil can escape into the intake…

Thanks for your comment. Almost everyone I spoke with was also incredulous that much oil could be consumed due to a defective PCV valve.

Imagine what went through my mind after starting the trip with the oil at the full mark, then at the first stop at 400 miles finding no oil on the dip stick at all. Then having to add 3 quarts to bring it up to full. The crankcase only holds 5.

But the only two things done to the van after arriving in Seattle was to have the valve cover removed and replaced, and the PCV valve replaced. So go figure . . .

Yeah, I’m thinking of submitting you to Guinness for “the most oil consumed as the result of a stuck PCV valve”. But I’m glad the problem is fixed.

Happy motoring.

Well, I guess I’ve heard of stranger things being submitted to the Guinness Book.

I’ll tell you what, after adding the 1st quart of oil and still not having it show on the dipstick, I dropped to the ground fully expecting to see it running out the bottom. But it was completely dry. The 2nd quart only got it to the very tip of the dipstick. And the 3rd brought it about 3/4 way between the low and full marks.

I don’t mean to over-dramatize this, but I’ve been working with cars since I was a drag racing teenager (I’m 62 now), and I know what 1 quart of oil for every 140 miles means. It was just so unbelievable. Now I better understand what the word surreal means.

I left a bit out of my story to reduce the verbiage, but it was actually my daughter, working with me, who had purchased the van from Craigslist after having a pre-buy inspection done on it at a Toyota dealership. Now it is apparent why the selling dealer was asking $1000 below Book.

I think what made this experience the worst was trying to think of the least-shocking way to tell my daughter the bad news. But I managed on the 2nd day on the road after confirming it was in fact using that much oil.

But what made this experience worth it, I guess, was when I got to tell her that a $10 part fixed the problem, and in fact she had made a good deal.

For a 33-year-old woman with a husband and 3 young children, it was a pleasure to see worry change to relief.

Yes, now she and her family are Happy motoring.

Thanks for your comment . . .

I know I’ve learned never again to doubt that a PCV valve can cause an extremely level of consumption. You given me a bit more knowledge today. It’s a good day.

Whats the flow chart on this one? The valve was stuck shut pressurizing the crankcase causing the oil to leak out or it was stuck open all the time? Are saying all this oil got sucked out of the engine crankcase and into the hose attached to the PCV and then into the intake and burned and you could not see it out the tailpipe?

A PCV valve mounted in the valve cover is not going to suck liquid oil out of the crankcase (or valve train area) and in to the intake to be burned in the combustion chamber. This stuck PCV must be sucking blow by gases that were heavy with oil vapors due to a engine mechanical problem.

Its engine mechanical problems that cause the engine to lose its oil out a stuck open PCV. The oil must be in the blow by gases for the PCV to get a hold of it.

Set me straight on this one.

Its going to get a “bump” someone better come up with a idea,something to make this possible.

Since no one has presented any type of explaination how a “defective” PCV valve caused this oil comsumption or what what actualy wrong with the valve this post must be sent to the “unconfirmed” holding area. We can’t pass this info along to our readers unless we can explain how things happened. UNCONFIRMED.

At 155k miles I would say the rings likely have a little blowby anyway. With a normal functioning PCV the cylinder walls will be wiped clean on the piston downstrokes by the oil wiper rings.
With a stuck PCV the excess crankcase pressure that now exists will have a tendency to try and force oil back past the rings and into the combustion chambers.

I wonder that his oil consumption went away. Blowby would not “go away”. The oil use by the blow by theory would not stop or reduce to the level reported. A quart in 140 miles thru the engine should be a cloud, at least pretty smokey. With the air cleaner 12 quarts of oil would make it an oil sponge dripping wet. Seems we are missing a detail or two. If the pcv were that stuck the why no blow by at the rubber pcv gasket on the valve cover etc. The amount of back pressure in the crankcase to push oil into the cylinders does not sound right for this much oil.

So the idea is that the PCV was stuck shut,pressurizing the cranckcase, this would cause oil leakage/seepage at all seal and gasket points,but this was not the case,there was no external oil leaksge.

At least we are moving close to saying that the engine does have a underlying mechanical condition and all was not made right by a new PCV, this is bringing some degree of sanity to the problem description and resolution.

It’s impossible sometimes to gauge the effects of things like this since the symptoms can vary quite a bit.

In theory, a stuck PCV will force oil out past gaskets and seals but what if the PCV were simply gunked up badly and the crankcase was becoming semi-pressurized so to speak. Combined with good, tight fitting seals it’s possible they may not leak.

I had a dealer send me a Jeep one time (6 banger) that was puking oil like crazy but only from one spot; the rear main. The PCV was good but the intake port in the manifold was caked solid with hardened deposits. This actually required a drill to clean out and once that was done the oil leak stopped.
One wonders why the rear main on this Jeep was the only leaking seal on the engine. Everything else was bone dry.

My memory is hazy on this one but it seems like I remember a Subaru doing something along the same lines. The intake port was caked solid and yet this particular car did not leak at all although there was an oil useage complaint.

The oil consumption the OP currently has could point to a little ring blowby although at a quart per 1k miles I wouldn’t worry that much about it.
That’s about my best theories anyway.

Where is the first catalytic converter located on the Toyota van? If it’s in the ex. manifold, and not after it then that narrows it down. I know that Nissan has major problems with oil consumption on their USDM 2.5 liter engines because of the location of the catalytic converter being too close to the cylinder head. Over time, the catalytic converter breaks down and some of the dust from it back flows (during scavenging effect) into the cylinders and wrecks the low tension oil rings allowing oil to burn off. My wife’s Nissan burned about the same amount of oil or more, usually about 2 or 2.5 qts per tank of fuel with no evidence of smoke out of the tailpipe whatsoever. No soot on the rear bumper. No oil seeping out of gaskets/seals. No oil spots on ground underneath. And it ran very good, despite the evidence of it burning oil when examining the heavily caked up spark plugs. I’m wondering if you have a kind of similar situation with the Toyota… What engine is in it? Where is the first cat located? Does its engine use low tension oil rings? When you turn it off from running at idle speed, does it wind down slowly to a stop or does the engine stop spinning quickly enough that it shakes the chassis a little? Has anyone done a compression test? What was the outcome after a while? I know this is an old thread, did the pcv valve fix it long term? What ever happened?

Did you not see that this is a 7 year old thread so they might not even have the vehicle anymore.

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