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


  • edited September 2009
    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.
  • edited September 2009
    I thought that was a very clear explanation. Thank you . . .
  • edited September 2009
    You're welcome.
  • edited September 2009
  • edited September 2009
    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.
  • edited September 2009
    Thank you. I appreciate your answer . . .
  • edited September 2009
    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..
  • edited September 2009
    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 . . .
  • edited September 2009
    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.
  • edited September 2009
    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 . . .
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