Lacquer Thinner and Catalytic Converter

Is it safe to clean your catalytic converter by pouring some lacquer thinner in your gas tank and running the engine for about 150 miles as Scotty Kilmer suggests in this video?

The p0420 code came on about a month ago, and it goes off and on intermittently since then - I’m hoping that that means that the problem is fairly recent and, if this lacquer thinner thing works, will get rid of the impurities that are launching that code.

I need some reassurance or some advice before I do this.


I can imagine no reason why this would work. Plenty of nutty things on youtube…

I don’t think it will do any harm, but like texases, I cannot imagine how it could do any good.

BTW - often on an OBD2 system, a catalyst code will get set when the real problem is that the oxygen sensors are getting old and slow to respond. Do your oxygen sensors have more than 100k miles on them?

Lacquer Thinner is mostly acetone…It’s a powerful solvent that can damage fuel system components. After it burns in the engine, there is nothing left to “get rid of impurities” in the converter or anywhere else…

If your vehicle has over 100K miles, try changing the rear oxygen sensor since that’s the part that is generating the code…

I would never run any amount of lacquer thinner thru an electric fuel pump in the gas tank. Most fuel pump assemblies have mostly plastic components. And if some plastics are exposed to lacquer thinner it melts.

You do it first:)


When you burn acetone (di-methyl ketone) or it’s close relative MEK (methyl-ethyl ketone) in your engine, it turns into CO2 and H2O just like gasoline does so I don’t see how it has any magic converter cleaning properties. Being aggressive solvents, they might clean your fuel injector nozzles.

@Manolito - Yes - well over 100k on the sensors. I’ll change it and see if that is the problem.

I knew it was too good to be true. What about cat cleaners? I haven’t really researched them, but are there any that might do the job?


I didn’t expect this to generate that many comments. I have to remember this website in the future!

Would the fact that the light goes on and off have anything to do with a bad o2 sensor?

“Would the fact that the light goes on and off have anything to do with a bad o2 sensor?”

–If you had the codes read, you might be able to tell.

"–If you had the codes read, you might be able to tell. "

Actually NO…When you read the codes…if an O2 sensor is bad it’ll give a false reading to the OBD-II system. If a cat is bad…the O2 sensor will set the same error to the OBD-II system. You can’t tell what’s bad by the reading. All you know from the reading is that the O2 sensor is saying somethings wrong. From there you have to do more tests to determine if it’s the O2 sensor or it actually is the catalytic converter.

I’m going to guess that you have a P0420. Here is a pretty good write up:

Basically the code is just set due to O2 sensor readings. These can be off from what they’re supposed to be b/c: there is a problem with the O2 sensor(s); something else is wrong and messing up the fuel/air mix (and the O2 sensor readings are fine); there is an exhaust leak letting air/exhaust in/out where it doesn’t belong (and the O2 sensors are fine); the cat is actually bad & not doing its job (and the O2 sensors are just fine).

Very good mechanics don’t guess about it. They find out.

The thing to do next is look at the signals coming from the O2 sensors with a graphing scanner or (oscillo)scope.
A good troubleshooter can tell whether the sensors are bad or they’re just indicating another issue.

I did a lot of googling on this, after I got the dreaded 0420 last weekend going down the mountains into Orizaba, at 3500 rpm in second. A lot of negative thoughts, but I also encountered on several forums people who had actually tried it, and it worked for them. It is kind of scary to think of pouring the stuff in my gas tank, though.

Lacquer thinner won’t damage your parts immediately. It will take time to dissolve parts to the point that they develop leaks. Still, anything that contains a variety of aggressive solvents will likely damage something in the fuel train given enough time. The problem in this case isn’t what you know that bites you, it’s what you don’t know.

Thanks for the posting. I especially liked it because that’s how I see it. Get the stuff in and drive it out ASAP to reduce contact with any parts that might be affected.

The few people who said they tried it and it worked, no one said they had any problems as a result.

My thought was to get two quarts of it, and use it when the tank is 1/4 full. Then, drive and drive until the gas is nearly gone, which should only be a few hours and fill the tank, which will dilute the remaining stuff to a very low level. I figure if I start with a 10% mix, drive it until it is nearly gone, and fill it, that would give me no more than 1 or 2% mix.

I need to do some math, and see if it’s better to drive it till the gas is low, then fill the tank, or only add a few gallons and keep driving a few more hours before filling the tank. Once I fill the tank, whatever percentage is there will be there for a long time. My mind isn’t clear on it, but the math will make it clear.

Speed limits here in the country are under 40 mph, so maybe I could run it in second at 2500 rpm.

I will ask my wife to bring back a new scanner/data reader in June, and try to get more data on it first. All I have is a cheap Actron code reader.

At this point, I can’t even say it hasn’t recently started burning oil and screwed up the the converter or something like that, on that long down hill run in second. I need to put on my thinking cap.

If things don’t clear up here in Mexico, if I have problems with engine or transmission, I will probably put more into it than it’s worth, because older cars are less likely to be stolen by bandits.

Save your money…In Mexico, P0420 is not an issue. It’s something to be ignored…

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js7b, thanks for sending along Scotty’s site. Because of Scotty’s site, I found two other sites and the third site I found demonstrated a ‘five-cent solution’ for shortening throttle response time plus getting the throttle to open virtually all the way - something I now know the throttle hasn’t done since day one of the vehicle’s life. The mechanic, jlsparky7, popping up on Youtube, said that some vehicles are purposely sent out from the factory with an extended response time. Oh, well. I’m happy. Thanks again, to jlsparky7 and js7b!

Save your money…In Mexico, P0420 is not an issue. It’s something to be ignored…

Not if you are required to pass smog verification. Fortunately, I am not. Not yet. They have discussed making import cars by retirees be verified, but not yet.

My area is one with smog verification for local cars. I am told for $50 USD all cars pass.

However, this is a Texas car, and eventually I will have to take it back, where it is required to have state inspection. They do not verify smog in McAllen, I can’t even find a shop to measure smog output. It was suggested I take it to Houston if I wanted to know how good it was on smog.

But, I am told there is a problem on state inspection, not sure if that is state wide. But, you are, or are not, it’s not clear, allowed one readiness failure whatever that means.

So, eventually it will have to be fixed.

More Googling. Still most comments are hypothetical, what I call guesses, how bad it is, and very few who have actually tried it, and they virtually all say it worked. Sigh.

I did find a lot of info on adding 2 ounces of acetone for each 10 gallons of gasoline, Supposedly increases miles unless gas has ethanol in it. Only one person said it cleaned his catalytic converter. And, a Dave Narby said he took a fuel pump apart and put the plastic parts in an acetone mixture twice as strong as the plan, and it didn’t harm them that badly over a long period of time. I do not think I will try acetone.

I do agree there is on rush on this, until September if/when I go back to Texas.

I had poured a gallon of lacquer thinner from Home Depot into a half tank of Shell premium gas in my 2004 Xterra. I drove down to San Diego at a constant speed of 65 m/h for one and a half hour. Unfortunately my P0430 Servise light did not go off. But added three more codes; P0420 pending Bank1, P0420 pending bank1, and P0430 pending bank 2. So now all four catalytic converters on this car are infected. I have about 160,000 miles on this car. May be it is time to change all of the converters. I tried this cheap fix and apparently not working at all.