Why Is Transmission Fluid Important And When Should I Change It?

Transmission fluid is a vital component of any vehicle's transmission system, serving multiple functions essential for the proper operation and longevity of the transmission. Let's explore why transmission fluid is important and how it works.

What Is Transmission Fluid?

Transmission fluid lubricates and cools the transmission, whether you have a manual transmission or an automatic. If you have an automatic transmission (as most people do), transmission fluid also helps provide hydraulic pressure, which helps the transmission change gears.

Important Things To Know:

1. How Often Should You Change Transmission Fluid?

The frequency of transmission fluid changes varies by model and how the car has been driven. A general rule of thumb is to check and replace transmission fluid every 30,000 to 60,000 miles, but again, check your vehicle's manual for the best advice. 

If you do a lot of stop-and-go driving, frequently haul heavy loads, or tow a trailer – all of which generate more heat and stress on the transmission – you should change the fluid more often than you would if you mainly do light-duty suburban or highway driving.

2. When Should You Change Transmission Fluid for Severe Driving Conditions?

You should change transmission fluid during high-stress conditions - manufacturers typically describe these conditions as "severe" driving:

• GM often recommends changing the fluid every 45,000 miles under "severe" conditions. For "normal" driving, though, there is no mention of changing the fluid.
• Toyota says to change the fluid every 60,000 miles for severe use; otherwise, it's unnecessary.
• Honda recommends that its continuously variable automatic transmissions (CVT) follow the Maintenance Minder on its vehicles, which monitors time and mileage and alerts the driver when service is needed. But if you do a lot of mountain driving or towing, Honda recommends changing the fluid every 25,000 miles.
• Ford's recommended interval for "normal" driving is 150,000 miles.
• BMW says to change the fluid every 60,000 miles.
• Mercedes-Benz says every 40,000.

As you can see, recommended transmission fluid change intervals are all over the board. Information about the frequency of transmission fluid changes should be in your owner's manual and the maintenance schedule.

3. What Does a Transmission Fluid Change Cost?

The cost to change the transmission fluid will vary based on the vehicle, whether it is a drain or a flush, and whether the transmission requires a new filter.

Some shops advertise fluid changes for around $100, but if you have a BMW, Mercedes, or other luxury vehicle, the cost can be in the $300 to $400 range or higher.

4. How Do You Test Your Transmission Fluid?

The appearance of transmission fluid can say a lot about its condition. Still, many contemporary vehicles don't have transmission dipsticks, so checking the fluid requires opening a drain plug – a job better left to a qualified auto repair technician.

5. What Color Is Transmission Fluid?

Transmission fluid is dyed red and translucent, so its color is a good indication of whether it contains any contaminants. As it deteriorates, it tends to turn darker. It should be changed if it is brown or black or has a burned odor. Those also could be signs of mechanical problems, so fresh fluid might not fix what's ailing a transmission.

Spending a few hundred dollars on a transmission fluid flush every few years could save thousands compared to paying for a rebuilt or new transmission.

The Bottom Line

Transmission fluid is crucial for keeping your vehicle's transmission functioning properly. But the frequency with which it needs to be changed varies widely depending on the make, model, and type of driving you do. Consult your owner's manual for specific recommendations and work with a trusted mechanic to keep your transmission well-maintained. A little preventative care now can save you from costly repairs down the road.