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Catalytic Converters, Oil Consumption, and the Environment

Hello All. I have a 02’ Chevy Prizm that consumes oil (common issue in the IzzFE engines that were in Chevy Prizms and 8th Gen Corollas). I see some who say it’s bad for the environment to keep driving a car like this. I see a fair amount of folks who suggest that with oil consumption, you just need to save up for a whole new engine or engine rebuild. But oil is cheap and the only parts that seem to wear out quicker are O2 sensors (cheap), spark plugs (also cheap), and the Catalytic Converter.

Maybe I am not seeing something here, but I recently got a new Caty from Rock Auto, delivered in less than 48 hours for $104, then welded on at my local shop for a total of $80.

I think of the Caty like a vacuum, and this car like a floor that consistently gets nasty. Well, as long as I am willing to buy new vacuums periodically, the floor can stay clean.

My question is, as long as I keep that oil topped off and replace the Caty as soon as the Check Engine Light gives an emission code, can’t I keep driving this thing for 50K more miles with the confidence that I am doing no damage to the environment beyond what a normal car does?


I think that the simple answer is, no you can’t. You are doing damage.

You car burns excessive amounts of engine oil, a complex hydrocarbon, that will overwhelm your catalytic convertor to the point that unburned hydrocarbons are being released into the atmosphere. If you stand close behind your car while it is running, does it stink? Does it blow blue smoke? I’d bet it does. Compare that to a proper running car. Not nearly as bad is it? The cat is not designed to process the sheer volume of hydrocarbons being pumped through it so much goes right out the tailpipe.

The correct, and most environmentally friendly fix, is to rebuild the engine currently in your car. That uses the least amount of resources to clean up your exhaust.

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If you’re going to try to put an environmental spin on this, you’re going to have a hard time justifying it. Catalytic converters are built using precious metals/rare earth elements with the idea that they should last 150k-300k miles. By replacing yours every 20k miles (maybe more, maybe less), you’re depleting those rare metals much, much quicker than would ordinarily be expected, More of these elements have to be extracted from the earth in a fashion that’s not very ecologically sound. Furthermore, your exhaust emissions will still be significantly higher than a properly running car would be. The catalytic converter in your car was designed to clean the exhaust of a properly running car, not handle several quarts of oil being effectively dumped into it every few thousand miles.

From personal expense point of view, it’s going to cheaper than getting the engine rebuilt at least in the short term. But if you’re looking for the earth-friendly solution, getting the engine rebuilt would be the way to go.


I agree with your overall conclusion. However, there are situations where an older driver who only drives 4000 miles a year or so, can keep this car running for a few more years instead of buying a new car which demands a very large environmental impact just to built.

However, as a daily driver for an active person, it needs a new engine or be sent to the crusher!

There are situation where poor design forces owners to just take off the converter. I felt like Thoreau in his essay on Civil Disobedience. Our 1976 Ford Granada with the Windsor 352 engine ran so poorly that an experienced mechanic told me to just take if off and put a plain pipe in between. Where we lived there were no annual tailpipe inspections and the car ran well with a clean looking exhaust till we sold it 10 years later.

This car was available with or without a converter depending on location. The ones without ran very poorly and the driveability of ours was almost as bad. I kept the converter in the basement in case we moved to an area where there were inspection, but sold the car in 1988 to a local guy who worked in the mountains and loved the big engine’s power and the torque…

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Of course, he can keep driving it until the cat plugs up, or until the CEL is illuminated and it must pass emissions again. And that is exactly what I would do, if I owned such a car: keep the oil topped off, and replace the cat only when performance becomes unacceptable, or it is needed to pass the emissions test. Even in a car which burns quite a bit of oil, the cat should last for several years–and can be replaced for a fraction of the cost to replace or rebuild the engine!

When I am driving at night, and stopped in traffic, I always look into the car to my left and to my right, and try to see their instrument cluster. More often than not, at least one car stopped next to me has the CEL and/or other warning lights illuminated and guess what? They get where they’re going just fine. As long as you’re not driving a “gross polluter” which emits a cloud of visible smoke, no one is going to bother you.

Agree with this post. Manufacturing a new car probably has a pretty significant environmental impact.

The way I look at it, driving that old car that burns a little oil for a few more years probably has less of an environmental impact than one politician flying his jet to the next environmental summit. :grin:

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These engines are also known for slinging oil from the front seal. It only does it with the engine running so it doesn’t drip much oil when parked. Easy to check, look for oil 90 degrees out from the front of the engine. Usually best seen on the fire wall

I was always under the impression that catalytic converters had a pretty big recycling value. I remember scrapping a junk car once and took the converter off to sell as scrap. I don’t remember what I got but it was definitely worth doing. The unfortunate side effect of this is that criminal scrappers often cut them off for dope money. I know people who have come out in the morning only to hear their engines really ROAR and wonder why. They find out someone got under their car with a battery sawzall and removed their converter to sell as scrap.

I can see there being resources used to break down and reprocess bad (or stolen) converters but would think that most of the precious metals would be saved.

Definitely check that engine seal as suggested. If that is all it is, you are going to have a relatively inexpensive repair. Even if you aren’t burning oil, letting it drip out on the ground isn’t good for the ground and water supply.

I don’t see the number of complete gross polluters on the roads like I used to. I mean you might get an old oil burning truck smoking pretty bad or that car that stink but has no visible smoke. Then you also get those letting out an occasional puff of smoke and the associated noxious smell.

I wonder if this is due to modern cars being much more sensitive so flooding sensors with burned oil will make them almost undrivable in short order, leading to expensive repairs that won’t last. The metallurgy and machining of engines has improved as has fuel management and lubricant technology. I assume this all plays a role. I also suspect a large glut of junk cars were turned in when Cash For Clunkers was going on.

I did see an older Intrepid not too long ago in a parking lot. It was white but the back end was nearly black with all the soot coming out the tailpipe. I would have bet money to a stranger in the parking lot that it had the dreaded 2.7L engine.

(This is a reply for FoDaddy and Mutangman but all can respond)

Thank you guys for the quick and thorough reply. You are saying, the exhaust from my vehicle is so different than what it was designed to deal with, that even with a brand new Caty on there, my emissions will still be worse than a normal car?

Also, it is a vehicle that gets close to 30 mpg. How much worse is it than a vehicle that gets half that but has no oil issues?

I’m not sure where you get your information

But we’ve had several Toyotas over the course of more than 40 years . . . and only one of them ever had a front crankshaft seal leaking

Not lately

Scrap values vary. Aftermarket cats are worth $5. Some are worth $30. Some over $100. Palladium was at an all time high recently, so they do have decent value.

How much oil is it burning? If less than one quart per 700- 1000 miles, seems like a workable plan. One note, the cat you purchased from Rock Auto is probably not the same quality, not as robust as an oem cat. It may not last as many years as the cat that came w/the car new.

Apparently this thing is using a lot of oil to cause Catalytic Converter and sensor problems and he wants approval to keep doing so. Well , I don’t approve and his thinking that he can get another 50000 miles out of this 17 year old vehicle might be called dreaming.

The 1zzfe of the late 90’s is prone to deposits clogging the oil control rings.
It would be worth it to try a piston soak:
Remove the spark plugs. Turn the crank 1/4 turn from TDC so all the pistons are about halfway down.
Pour a strong solvent into the plug holes until near full.
Let soak for 4-8 hours. Wiggle the crank a little and refill every hour or so.
Lay a heavy rag over the plug holes and crank with the starter to blow out the remaining solvent.
Squirt a little oil in each hole to re-lube the cylinders.
Replace the plugs and start the engine.
Let it run a couple minutes until it clears the cylinders and stops smoking.
Change the oil. Use synthetic oil going forward. It will better resist deposit formation.

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Yes, your car is emitting more pollution because of the burned oil. You are emitting excess hydrocarbons because the cat can’t break down the hydrocarbons into water and CO2.

Your 30 mpg car emits less CO2 than a car getting 15 mpg but FAR, FAR more hydrocarbons. Hydrocarbons are a very strong greenhouse gas. How much more? Depends on how much oil you burn. Your actual question was if you were a polluter. You are. More than an SUV.

Seem like you are trying to parse the argument to justify driving this polluter to your greenie friends and your own conscience. You started the discussion as an economic question. As as others have posted, the cheapest solution was to continue to add oil and replace O2’s and cat’s until the car died. The solution you didn’t really want to hear was that, yes, you are a polluter and it will cost significant money to solve that.

This is clearly a microcosm of the worldwide “green” debate. There is a large economic consequence to a “green” agenda for any country.

I wouldn’t say I am trying to parse the argument, just trying to get clarity. If I put all my thoughts and questions in my first post, it’d be over a page. So generally, the better approach is original question or two, then follow-up question for clarity. But yes, you are right, it is a matter of conscience. I don’t want to drive a majorly polluting vehicle. I thought the MPG question was a legitimate follow-up to help me understand just what level of polluter I am. Like a SUV driver or worse. You’re definitely in the camp that it is worse, and you seem to make an intelligent argument.

That being said, in one line, you say “your actual question was if you were a polluter.” A few lines down, you say, “you started the discussion as an economic question.” From the start of the discussion, my inquiry was both economic and environmental. AND the line “Seem like you are trying to parse the argument to justify driving this polluter to your greenie friends and your own conscience” seems very presumptive. It makes me think if he’s that presumptive about who I am, he’s probably presumptive in analyzing my car situation. It makes me less likely to trust your assessment. I mean I still think you are probably a smart guy offering expertise, but now there’s a little bit of doubt in my head. I bet if you left such comments out, more people would trust your advice, and you would really end up having your advice help more people.

My opinion is that your looking for validation that it is alright to pollute with your vehicle . I say it is not. There is no purpose trying to compare your vehicle to any other vehicle. If you really want to drive this what was basically a throw away vehicle then have it repaired , detailed and drive it like it might be a rarity on the road.

As for Mr. Mustang if that is who you are referring to : He is one of several regular posters here that should have a 5 star out of 5 beside his screen name.

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This was your question. No mention of economics.

I don’t care if you trust my assessment or not. I am not validated by someone from the ether of the internet. If you don’t trust it (or @FoDaddy’s either), do your own research. Any presumptions I’ve made here are based on what you wrote and they are my own.

I’ve had two, and they both leaked.

There are several things at play here.

  1. Aftermarket catalytic converters aren’t the same as OEM, One of the reasons they tend to be cheaper is that they are often made with less substrate surface area. They don’t have to meet the same emissions warranty requirements as an OEM converter, so costs are cut in order to make them cheaper.

  2. Because they aren’t made to same standards as OEM converters, they aren’t going to last as long even under ideal conditions and certainly not as long with a steady diet of oil going into them.

  3. The converters are made to meet emissions standards with a properly running engine. When you introduce a new variable, (in this case a few quarts of oil every few months), then all bets regarding emissions are off, the oil will get burned off, this will result in a noticeable increase in emissions.

  4. The catalytic converter was not designed to burn off motor oil, it will get contaminated and will be rendered ineffective at some point. A cheap aftermarket converter will likely not last nearly as long before becoming contaminated as the OEM one did.

Hard to say, It would depend on the amount of oil getting burned off, if it’s something like a quart every 500-1000 miles, then it’s probable that it’s effectively producing more greenhouse gasses than a say a new Tahoe, or even a Tahoe of the same vintage that’s running properly. Your car is definitely not as earth-friendly as it once was.

I like I said before. From a monetary standpoint, you’re probably going to come out ahead just topping off the oil and throwing a new cheap cat and/or O2 sensor(s) on it every other year for the next 50k miles. From an earth-friendly standpoint, getting the engine rebuilt and continuing to drive the car for another 100k miles would be a better option than buying a new car, but it’ll still cost you significantly more.