Why You Need to Change the Transmission Fluid Why You Need to Change the Transmission Fluid

If you’ve had your car serviced at Express or Firestone lately, the mechanic probably told you to change the transmission fluid every 30,000 miles, and there are good reasons for that. What some car owners don’t realize is that the automatic transmission fluid (ATF) wears out and overheats, and over the long haul this isn’t good for your car.

Why the Automatic Transmission Fluid Wears Out

An automatic transmission generates heat via friction, including that of the fluid within the torque converter and during clutch plate engagement. In addition, there’s friction and heat produced by the bearings and gears due to their loads. When your car is running the transmission fluid starts to heat up. Under normal driving conditions the ATF temperature will hit 175 F, and that’s the temperature these fluids are supposed to run. If the temperature doesn’t change the ATF can be used for up to 100,000 miles or so, but it does change and often goes higher. The higher the temperature gets, the more likely trouble will occur.

What Happens When the ATF Temperature Increases?

As the temperature goes up, the ATF turns brown and oxidizes, and the smell begins to resemble that of toast. The heat slowly destroys the fluid’s friction and lubricating properties, and varnish starts to appear on the internal component, interfering with the transmission’s functions.

If the temperature goes over 250 degrees F, expect hardening of the rubber seals, and if left untreated will lead to pressure losses and leaks. As the temperature continues to go higher you’ll notice the transmission start to slip, and this leads to even more heating.

To give you an idea of the effect of overheating, the transmission fluid at 195 F reduces life expectancy to 50,000 miles, while at 220 degrees the fluid is good for only 25,000 miles, and if the heat level reaches 300 degrees F, the ATF will be lucky to last 1,000 miles. Given these numbers, it’s crucial you keep the ATF in good condition as well as the rest of your car.

What Causes ATF to Rise?

While experts recommend you change the ATF every 30,000 miles, you’ll need to change it sooner if the car is constantly towing a trailer, frequently goes through stop and go traffic, travel at high speeds during hot summer days or drive along mountainsides and rugged terrain.

The ATF will also heat up if you keep pushing the transmission in an attempt to pull it out of snow or mud, and overheating can also arise from problems with the built-in cooling system, the radiator, fan, clutch, thermostat and so on.

How to Cool the ATF

Most cars have a heat exchanger at the radiator’s end tank or near the bottom, so when the hot ATF circulates, the exchanger cools it down, but its efficiency depends on the radiator, which could be from 180 to 220 F. If you think the built-in cooling system isn’t effective you can go for an auxiliary cooling system, which any car service can install.

An auxiliary cooling system can significantly reduce the ATF temperature, prolonging the fluid’s life. The fin/plate type is a bit more effective than the fin and tube design, but either one of these can lower the temperature by 80 to 140 degrees if properly installed.

Types of ATF Fluid

The question now is what type of automatic transmission fluid should be used. There are different types, and you can find the appropriate one in your owner’s manual. You can also check the transmission dipstick because it might be stated there. If you’re driving an old Ford odds are you’re going to need a type F, but it will different for others.

It’s imperative that you use the correct fluid type for your car because the wrong type can have an adverse effect on the shifts and movement. If the wrong fluid is applied for instance, that could make the transmission shift too much, and in other cases it can weaken the unit and lead to rapid wear.

Changing the ATF

This is a complicated process because you’re not going to find a drain plug for the fluid change, so it’s better to let a professional do this. If you want to do this yourself you need to get under your car and take out the pan from the transmission. Fluid will come out so make sure you’ve got a big pan to catch them. A standard fluid changer requires 3 to 6 quarts of fluid, a pan gasket and a new filter.

Make sure the transmission fluid isn’t filled to the brim because that can lead to foaming and cause the transmission to shift erratically. Again, the changing process is a complex one so if you’re going to do this yourself make sure you know what you’re doing.

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