How Does Transmission Fluid Work and Why You Need to Change It
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Your transmission plays an essential role in your car accelerating, cruising down the highway, and achieving optimal fuel economy.
Transmissions have four or more gear ratios, and the ability to change between them is vital to vehicle performance and safety.
As your transmission quietly shifts through the gears every day, you may not pay much attention to the transmission fluid or consider when it needs to be changed.
But how do transmission fluids work? What’s the cost to change transmission fluid?
Let’s take a closer look at transmission fluids, how they work, and when you need fresh fluid.
How transmission fluids work
Typically, a vehicle has either a manual or an automatic transmission.
With a manual transmission, the driver performs gear changes themselves, usually via a stick shift, and decides when the time is right to change ratios (or gears), like from first to second and from second to third.
But with an automatic transmission, gears switch in an automated fashion, allowing the driver to simply press the accelerator and go.
Since manual and automatic transmissions function uniquely, each requires a specific transmission fluid grade.
Manual transmission fluid acts as a lubricant to protect parts like gear ratios or bearings.
But on automatic transmissions, the transmission fluid plays a more significant role.
Automatic transmissions use a hydraulic device called a torque converter. The torque converter receives the torque from the motor and converts it into usable power so the vehicle can move forward.
The transmission fluid works inside the torque converter to make this conversion happen. That means automatic transmission fluid transfers the power from the engine to the tires on the pavement.
Because of this critical function, automatic transmission fluid (ATF) wears out quicker than that used in manual transmissions, and you need to change it more frequently.
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When should you change transmission fluids?
Like the engine oil, you need to change your transmission fluid from time to time. But the frequency depends on the make and model of your vehicle, transmission type, and driving conditions.
Some vehicle manufacturers recommend vehicle owners follow 100,000 service intervals for their automatic transmissions, while others, like Ford, let you drive as many as 150,000 miles before fluid replacement.
However, many mechanics believe this maintenance schedule to be too lengthy and advise new transmission fluid around every 50,000 miles.
With the fluid in automatic and manual transmissions serving different purposes, consulting your owner’s manual gives you the best idea on when it’s time to switch it out.
Like engine oil, transmission fluid degrades over time, even more so when driven under demanding conditions. If you frequently drive in stop-and-go traffic, perform towing, or transport heavy loads, the additional heat produced pushes the limits of both the transmission and the fluid, speeding up degradation.
But while engine oil is mainly a lubricant, automatic transmission fluid performs several duties, including facilitating hydraulic gear changes, cooling the transmission, and providing lubrication.
When you regularly drive in situations that strain the transmission, it’s essential to frequently check the fluid level yourself and have a mechanic monitor its condition.
Typically, transmission fluid is red — although some the color of brands may differ— and turns darker as it breaks down. It’s also essential to pay attention to the smell of transmission fluid because a burned odor may indicate it’s time to change it or other more serious mechanical issues.
How do you change transmission fluids?
Now that you know the importance of your transmission fluid, following a series of steps can ensure you change it properly if needed.
First, check your owner's manual to determine the recommended service interval for transmission fluid changes. Or your car might have an indicator light alerting you to the need for a transmission fluid flush. With that information, it's a good idea to visit a repair facility and have them check the fluid's condition and advise you on the next steps.
At that point, you can either pay a mechanic to perform a transmission service or do it yourself. If you decide on the DIY route, following a specific process is essential.
First, you'll need several tools and other items, including:
- Hydraulic jack or ramps
- Wrench to drain old transmission fluid
- Pan to hold discarded transmission fluid
- Transmission pan gasket to seal it
- Recommended type of new transmission fluid
- Transmission filter
With those supplies on hand, it's time to remove the old fluid and pour in its replacement. First, let your vehicle cool down. Then, after raising the front of your car with a jack or ramps and applying the emergency brake, locate the transmission fluid pan and, using the wrench, remove it bolt by bolt. Next, let the fluid drain into the catch pan below.
With the fluid fully drained into the catch pan, remove the old filter and install the new one.
Now move the new gasket into place, ensuring a proper seal between the pan and transmission.
After reinstalling the transmission pan bolt by bolt, pour in the recommended amount of fluid, using a funnel to avoid spills or drips. Always make sure to use the fluid grade recommended by the manufacturer, or your transmission could incur damage.
With the fluid change complete, it’s time to dispose of the old fluid, which contains many harmful chemicals and additives. Gather the old fluid in jugs or sealed containers, and take them to the nearest recycling location.
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April 15, 2022
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