Carbon Flushes

I had a carbon flush performed on a VW '95 Eurovan, and ever since it runs fabulous. It gets better gas mileage, idles better etc. I was told by another mechanic that I could do my own carbon flush by adding 1 gallon of Rubbing Alcohol to every 10 gallons of fuel. He said that this would make the car burn hotter thus burning off excess carbon build up in the engine. My questions are 1)Is this true?, 2)How often can a carbon flush can be performed? 3)If it is recommended can I do it to my wife’s 2003 Honda Civic?

Thanks, Ed

Rubbing alcohol contains water and most of it contains other chemicals. If you want to put alcohol in, find an E85 pump. I’ve taken more than a half dozen vehicles over 200K and have never done this foolishness.

Decarbonization of an engine can improve performance and fuel mileage.

Carbon deposits can form on the backsides of the intake valves. When this happens it can effect how efficiently the fuel/air enters the cylinders. And if there’s a lot of carbon buildup on the valves, this carbon can absorb some of the fuel that was meant to go into the cylinders.

One effective way to decarbonize an engine is with a can of SeaFoam Engine Treatment. Follow this procedure.

Get the engine up to operating temperature and shut off the engine.

Disconnect the vacuum hose from the brake booster.

Adapt a hose that fits into the end of the brake booster hose and into the can of SeaFoam.

Pinch this hose off with a pair of pliers.

Have someone start the engine, and bring the engine up to about 2,000 RPM’s.

Slowly open the pliers so the SeaFoam starts to be drawn into the engine. Here you’ll have to keep the RPM’s up and meter the amount of Seafoam entering the engine so it doesn’t stall.

When the can of SeaFoam is empty turn off the engine for about a half hour.

Reconnect the brake booster hose.

Restart the engine and bring the RPM’s back up until the smoke clears from the tailpipe.


I would stay away from rubbing alcohol. There a number of commercial products you can pour into your tank that provide cleaning action for your fuel system and combustion chambers. I use to put “Carbout” in the gas tank of my carbureted car several times a year. It did a great job. It souns like your Eurovan may have benefitted so much because a lot of crud had accumulated.

Yes, you should put the modern version of Carbout in both vehicles regularly. It’s called a variety of names but fuel injector cleaner and other names are common. This is very much cheaper than paying for an expensive carbon flush, whatever that is. Our 1994 Nissan has had a regular diet of these additives in the tank and runs just great.

Rubbing alcohol will not work! I did this once on an air-cooled VW by slowly pouring a quart of diesel fuel into the carburetor as the engine ran. It smoked like hell and it was very difficult to keep it running, but it purred like a kitten afterward (I would not even think of trying this on a modern, fuel-injected engine).

Stick with something specifically designed to remove carbon. Rubbing alcohol is NOT such a product.

After 3 days of city driving, the carbon starts to build up again. It’s not the same as the stuff you had removed but it’s a start. I used to flush my 76 Impala when I got to the first hill and the engine would start to ping. I put it in second gear and floored the pedal until I had a great black cloud behind the car. It stopped pinging. You don’t have to get yourself in trouble because that method isn’t such a good one. The water in the rubbing alcohol will cause rust. I don’t recommend it. I think my method is better than that.

Several people have addressed the rubbing alcohol so I will skip that one

2)How often can a carbon flush can be performed? 3)If it is recommended can I do it to my wife’s 2003 Honda Civic?

Let’s go to how often should it be performed. You could try it ever tank full, but that would likely do more damage than good. Following the instructions below I would suggest that while it depends on the car, yours likely has not had it done since 1995. I would suggest once ever year or two would be fine as it appears your current car and style of driving etc. seems to build up the need. So next winter try again using the instructions offered here. If there is no effect, then try it in two years.

I have never had a car that needed it. I have had several cars over 150,000 miles. Don’t buy the story that you need to drive your car like you stole it to keep it clean, I drive like a little old lady. Some cars just seem to have the need some don’t.

BTW you are likely to see other opinions as to how often it might be needed. I suggest each case is different, and each recommendation is equally valid and fallible.

Good Luck

After tearing down many engines, sometimes heavily carboned, usually lightly carboned, sometimes with negligable carbon, I would guess that the selling of de-carboning is a profitable but often unnecessary manintenance cost. However, on some engines it is greatly needed and will both improve performance and prolong engine life. A fiber=optic scope can inspect and determine the need for such maintenance and those who offer such service should base their recommendation on a view of the combustion chamber.

A little tap water dribbled slowly into the intake while the engine is running will clean out carbon.

I’ve done both Testers’ and OKs’ method . . . both cause a lot of smoke, OKs a bit less. I would suggest that you allow someone with a bit of experience to do the carbon flush, and stay away from the rubbing alcohol. Some folkd have talked about good results with a bottle of Techron every 2nd oil change. You just pour it in your gas tank when it’s about 1/4 full and run it. Good luck! Rocketman