Automatic Transmission Fluid Revisited

This car-care article appeared in my newspaper on October 28, 2003
Drive It Forever By Bob Sikorsky
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An article in Automotive Engineering magazine, the official publication of the Society of Automotive Engineers, brought to light a great deal of valuable information about automatic transmission fluids (ATF). ATF is probably the most complex of all auto- motive lubricants, including even the most sophisticated synthetic motor oils. They can be made from as many as 15 elements. A typical motor oil may contain seven. According to Automotive Engineering's article, transmission fluids are subjected to severe oxidizing conditions that can cause: * Deposits of sludge and vanish in the transmission; * An increase in corrosion of copper-alloy bearings; * Hardening of various elastomeric, or rubber-like, seals; * Glazing, flaking and wear of clutch plates and bands. Any one of these conditions ls bad news for your transmission and wallet, but all can be avoided by changing to a high-quality transmission fluid before oxidation can alter its protective characteristics. The big question is how to know when that time has arrived. A good rule of thumb is to follow the change interval given in your owner's manual. For most transmissions in most areas of the country this will do just fine. If you want to be more precise, just use the time-proved paper towel test. Here's what to do. Place a drop or two of transmission fluid from your car -- you can get the drops by removing the transmission dipstick -- on a clean piece of paper towel. Next to this drop, place another one or two drops of equal size of fresh unused transmission fluid. Wait one hour, then observe the spots. The fresh fluid spot is your reference point. It will be large and have a reddish or light-brown color. Compare your transmission fluid's spot to the one made by the fresh fluid. Is it about as large as the fresh fluid spot, and does it have some red or light-brown coloration? Or is it a small dark spot? Automatic transmission fluid that does not exhibit good spreadability and coloration is probably suffering from oxidation and should be replaced. A spot 'that approximates the color and size of the fresh fluid indicates that the fluid is still fine and should be left in the transmission. This test is easy to perform. It should be done about every two months As soon as you notice the fluid getting darker and the spot getting smaller and more concentrated, you will know it is nearing time to get the old stuff out and the fresh stuff in. One of the toughest decisions a car owner can make is whether or not to change the fluids for the first time after a number of miles have accumulated. At first this doesn't seem to be a problem -- fluids should be changed periodically. While that is true and the rules applies to all fluids in the car -- power steering, brake, coolant, oil, rear axle, transmission -- there are times when an owner is caught in a Catch 22. Here's a typical scenario. A car owner who has never changed the automatic transmission fluid decides that he should take better care of his present buggy. So, he thinks, I'm going to do it a favor and start by changing the transmission fluid because that would be the most expensive unit to replace. . He does, but to his dismay, in a few days he finds the car dripping transmission fluid from both front and rear seals. The car had never leaked with the old fluid, why should it leak now? Isn't fresh fluid supposed to be good for the transmission? It's leaking because the owner's neglect allowed crud to build up inside the transmission causing the viscosity of the fluid to thicken and become a "false" seal. The crud locked in the old fluid and kept it from leaking past the seals, which in the interim had become damaged. When fresh fluid was added to the transmission, the new additives attacked the false seals and opened a path through the bad seals so the fluid could escape. Result? A leaking transmission. New seals and/or gaskets will solve the problem. To change or not to change, that is the question. Is an owner better off with old fluid and a nonleaking unit or with fresh fluid and a leaking unit? Talk about tough decisions, but the answer depends on how long you intend to keep the car. If you plan to keep the vehicle, you're better off with fresh fluid. New seals or gaskets, if required, are an extra cost, but not as expensive as a new car. If you're going to get rid of the car, why ask for trouble? To add to the confusion, sometimes when fresh fluid is added to a high-mileage vehicle for the first time, it might not cause the unit to leak. That could be the case with your car, but there is no guarantee. If you decide to change any fluid for the first ' time in a car that has more than 70,000 miles on it -- there is really no way to set an exact number of miles -- you are, in essence, rolling the dice. -------------------------------------- Bob Sikorsky, is a national-award-winning journalist who has written several best-selling books on automotive care. Questions or comments of general interest should be addressed to Bob Sikorsky, care of this newspaper. Bob Sikorsky regrets that he cannot answer questions individually.
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Great article! I will use the tip given to diagnose my trans fluid from now on!
Al Kondo

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The article only mentions leaks as the potential problem of changing the ATF. I have heard it could cause the trans to malfunction also.
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Yes, you will get a varnish build up on a poorly maintained trans, once the fuid is changed with HIGHLY detergent ATF it cleans out all the varnish and those tight clearences built by varnish will disappear. Good trans to bad, with only a fluid change.
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Thanks,

Darryl Skelton
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Darryl " Charter" Skelton wrote:

Yep. Seen cars that after changing the fluid for the first time at 100,00+ miles, wouldn't even go into gear! Most people should be changing the trans fluid at 15,000 intervals just to be safe given how much auto trans rebuilds cost nowadays.
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Steve

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True enough, but it won't keep you out of the trans shop forever. The clutches and bands in ATs are wear items. Sooner or later you'll be out of time. Keeping the fluid clean will definitely help it be later though.
Steve wrote:

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Jim wrote:

Sure. I relate it to you have X number of shifts and everytime it shifts, 1 more is gone. Once you have X number of shifts, he clutches are gone!

From what I've seen with these late trannies, most failures are from crap being pumped through the valve bodies from hard part failures like bushings etc. Seems like lubrication issues rather than clutch problems? Cheap insurance considering the thousands of $$ a rebuild costs.
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Steve

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