The "ATF Trick": The Real Truth

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If you have been involved in the RX-7 community, you have probably heard mention of the "ATF trick", or "ATF treatment". It is often prescribed for serious flooding situations, and sometimes as a general maintenance item. Especially on a certain forum. However, misunderstandings about the use of automatic transmission fluid, or ATF, in rotary engines has caused damage to quite a number of cars. I am hoping that this page will provide a little info on the "ATF trick" that is rarely heard.

Basically, the ATF trick consists of introducing automatic transmission fluid into the working (combustion) chamber of a rotary engine. This is usually done by removing the leading spark plugs, and using a funnel and tube to pour a few ounces of fluid into the engine. The engine is then either rotated by hand or cranked over with the starter to distribute the fluid inside the engine. Common practice is to then leave the car overnight to allow the fluid to "do it's magic". The idea is that ATF dissolves any carbon deposits and cleans out the internal mechanism of the engine. ATF is also used in a situation of severe flooding. It is again poured into the engine through the spark plug holes. The ATF absorbs the extra fuel, and allows the apex seals form a better better seal and build up compression. The engine then starts and burns off the ATF.

The problem is, quite a number of people use the ATF trick as a general cure-all. What they don't realize is that ATF is in fact bad for the engine. ATF is a fairly corrosive liquid, designed for the environment in an automatic transmission. The seals and materials in an automatic transmission are different than those in the working chamber of your engine. While ATF may not be corrosive to the bands, clutches and gaskets in an automatic transmission, it is corrosive to carbon (which is good, and why it cleans the engine) and has been shown to affect the rubber O-rings used to seal the rotor housings together, as well as the o-rings used on the oil seals. ATF attacks all those seals, and if they were marginal to begin with, they will most certainly be ruined by the ATF trick. This is why there are so many complaints that sound like "I did the ATF trick a week ago and now my car smokes and burns oil". The ATF has damaged the seals, allowing oil to leak into the working chamber and be burned off. This is bad, and can only be cured by replacement of the seals, which of course requires disassembly of the engine. Since the ATF trick is most often used on marginal engines to try to increase the performance, problems are fairly common. So using ATF as a general "cure all" or engine cleanout method is not a good thing.

Another use is to try and free an engine that has become "carbon locked". Carbon locking occurs when a chunk of carbon dislodges from the rotor housing and jams the apex of the rotor against the housing. This prevents the engine from turning. ATF is poured into the engine in an attempt to dissolve the carbon. This procedure is entirely acceptable, as a carbon locked engine is usually on it's last legs anyway, and there's not a lot that can be done to make it run any worse. Because of the damage caused by carbon locking, the engine usually blows shortly after the carbon has been cleared.

Excessive use of ATF also has other side effects. For one, the spark plugs are fouled much more quickly. This is due to the deposits that build up as the ATF burns. It may not be a big deal, but fouled spark plugs need to be replaced otherwise they will cause loss of power and gas mileage. The same deposits that clog spark plugs are also blown into your exhaust. If you are running catalytic converters, the soot and forign matter may begin to clog up the honeycomb inside. If the converters were already marginal to begin with, the ATF treatment may be the "last straw". Of course, the engine oil should always be changed after using ATF since it will be contaminated. A slightly more amusing side effect are the intense clouds of strange-smelling white smoke. Be aware that the ATF trick will produce enough smoke to fill a neighbourhood quite effectively. This has resulted in concerned neighbours calling the fire department, police, etc.

The original use for ATF was to clear flooding. It is entirely acceptable in a situation of severe flooding to use ATF to restore engine compression and allow the engine to be started. ATF does not usually sit in a flooded engine long enough to cause damage to the seals, as shortly after the ATF is poured into the engine it is burned off on startup. However, oil works just as well and is much more benign.

There you have it, when you can and when you cannot use ATF. I hope that this saves at least a few cars out there.

Note: I have received alot of flack for this page. Many people were confused by my previous use of the term "side seals". What I really meant was "oil seals" or "oil o-rings". My mind always reverses them whenever I talk about the engine internals. This serves to confuse alot of people, and make me look like an idiot. I have corrected the terms above to make things more accurate. Obviously, ATF cannot attack the side seals in the engine because they are metal. The "ATF debate" is also not new. It has been going as long as there have been rotary engines, and won't stop anytime soon. Some have said ATF is the best thing since sliced bread, others have had their engine seriously damaged. This page is based on my experiences with ATF, and the fact that I personally know owners who have ruined their engines with this "fix all". For what it's worth.

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