Thread: ATF in your Oil

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Automatic transmission fluid has about the same viscosity as 5W-20 motor oil. The transmission fluid does not have the detergents that a first tier engine oil has. As such, transmission fluid has less cleaning power than a good 5W-20 oil.

Originally Posted by DennyW

correct Glenn... When I worked at a GM dealer. the carbon removing liquid they used...boy, talk about smoke...half can through carb...then flood the engine with the other half to stall it, let sit, then start and clear it out. The directions were right on the can.

Also, SeaFoam is very good if used right...

I have used the old style ATF (type "A") to clean engines back in the 60's when a high milage engine was +60,000 and learned to be cautious on the high mileaged engines. If you run it too long, you ruin it. I have also (old school) used diesel in the oil to clean it out and had sucess with that. I have also used the water to clean the carbon from the pistons and clinders with great luck. I have never run one more than 2 minutes though.
Wish I had known about the cleaner the dealers used. I would have tried it.
A great tip from the past though.

We did all the time back in the 70's and 80's for older engines, never ever had a problem. The old timers that did it swore by it, they also did the kerosene trick but I never tried it, the auto trans fluid seemed to work for me. I have been told that auto trans fluid is very high in detergent, that's why it works so well.

I have heard that 1 qrt transmission fluid does work well to clean an engine gently. I have a 1989 Buick full size estate wagon that I use Marvel Mystery oil in the oil (1qrt with 4 qrts regular 10w30 motor oil) and I also use it in the gas with every fillup (8 oz for 16 gallons) What a difference it made in acceleration and smoothness of the engine (the car has only 35K original miles with the olds 307 engine) When I bought the car it was very sluggish. After 1 oil change and 2 tanks of gas it was a totally different car. It will actually get out of its own way now Don Jr.

We used to add the a quart of tranny fluid to the gas tank with fillups when running in the high plains desert. It increased the vapor izing point of gas and prevented vapor lock in the old dodge vans we were using. Worked like a charm. The dodge boys claimed it would lubricate the engine too!
I'm always fearfull of miracle cures and quick fix solutions. But there are a few out there that have worked for me in the past.

Rebuilt the motor in my '91 Ford, 300-six. Motor was balky, didn't want to pull under 2K rpm's, missed over that. Suspected gummed up injectors from having sat for 6 months. Poured one quart of Type F auto trans fluid to 15 gals of gasoline and ran it through. Repeated with another 15 gals of gasoline. Truck smoothed right out, now pulls hard from idle to rev limit, no missing. Have not emission tested motor since then. Don't know if the 60:1 ratio of fuel to oil would do any harm to the catalytic converters, but it sure fixed the injectors.

Conventional transmission fluid and 5W-20 are both “highly refined mineral oil”. The average viscosity for transmission fluid at 40 degrees C is +/- 42cSt and 5W-20 is +/- 48cSt. Both contain detergents however; by composition, motor oils typically carry a greater percentage of the detergents.

API ratings of “SJ”, “SL”, or “SM” all contain high detergent content to lessen tailpipe emissions. API “SA” and “SB” ratings were the last totally "non-detergent" oils and these oils were typically single grade, i.e., 30W – and have not been commercially available for some time. Synthetics are a different composition altogether.

I think where people often see ATF working a cleaning agent is if they have been using “heavier viscosity” oils or have been running their engines a bit low on oil and deposits have started to build up. The introduction of transmission fluid in such cases would certainly lower the viscosity allowing suspension of particulate matter (carbon) which makes the oil look very dark. Performing this procedure on an older engine can have a very impressive result in the first oil change.

Several products have been introduced over the years (anyone else remember Rislone? - Basically the same effect as Techinspector w/ some tranny fluid in the gas.) that worked to varying degrees.

I know that everyone has an “oil story” where they ran 80W or straight STP in an old engine with a bazillion miles on it. My point was that modern 5W-20 does a fine job without any additives (transmission fluid or otherwise) on an engine that sees regular oil/filter changes.

Regards All,
Glenn