When Should You Check Transmission Fluid?

A car's transmission is a vital part of the vehicle, and when it is not maintained correctly, it can turn into a hefty repair bill. To help your car's transmission last longer, we researched this topic to give you a detailed guide about checking your transmission fluid. 

You should routinely check your transmission fluid at least once a month. Check the fluid along with your engine's oil to ensure that any transmission problems will not catch you by surprise.

Read further to learn more about when you should change your transmission fluid, and which replacement method is best for your transmission's longevity. 

A collage of a man checking his car and a hand pouring transmission fluid, When Should You Check Transmission Fluid?

When Should You Check Transmission Fluid? 

The most important part of maintaining a car is by routinely checking the fluids to ensure they are in working condition. A car's transmission fluid can reveal signs that it needs replacement and that the liquid has reached the end of its lifespan. 

You may also notice any loss of transmission fluid that could be a sign of future problems. Creating a schedule of checking your transmission fluid every month is an excellent way to stay up-to-date on your car's condition. 

Car manufacturers typically recommend that you change your car's transmission fluid every 60,000 to 100,000 miles for automatic vehicles. This number can depend on the condition of your car's transmission fluid. A transmission fluid that has changed colors and accumulated debris should be changed quickly to restore it into its proper state.

Sudden Transmission Problems

While routinely checking the transmission fluid is always a good idea, you may also need to check it immediately if problems arise. 

If you are driving and start to notice your transmission slipping or making grinding noises, you should check your transmission fluid immediately. A slipping transmission may signal that the fluid has been worn out and is working inefficiently. Worn-out transmission fluid will be a dark brown or black color with specks of dirt and debris in the liquid. 

A transmission fluid filled with debris will cause the transmission to be out of sync and not change gears properly. If you notice your car having trouble shifting gears and will not pick up speed after switching gears, it's time to get your system checked out by a professional. 

A grinding transmission noise may signal that your transmission fluid levels are low or you have more significant problems. A lack of transmission fluid will cause some gears in the transmission to grind together because of inadequate lubrication. 

Do You Check Your Transmission Fluid When it's Hot or Cold?

Before performing any routine maintenance on your transmission fluid, consult the owner's manual first. Each car has a different method of checking the fluid. Some car manufacturers like Honda will advise you to get the car's engine hot before turning it off and checking the fluid. Other manufacturers will ask you to keep the vehicle running while you check the fluid.

In most cases, the ideal way to check your transmission fluid is when the car is both hot and cold. In most models of vehicles, they have labeled the transmission fluid dipstick with both "Hot" and "Cold." These labels give you a measuring point depending on if your car is hot or cold. 

Temperatures Effect on Transmission Fluid

The fluid in a transmission reacts differently depending on the environment. If your car is hot, the liquid will expand and show a higher rating than if it was cold. Cross-checking your transmission fluids in both hot and cold environments is the ideal way to get an accurate reading. 

You can determine if your transmission needs more fluid if both the cold and hot readings show you are low on fluid. If you have enough transmission fluid, the liquid will cover both markers.

How Long Should I Let My Car Run before Checking the Transmission Fluid?

To ensure you receive an accurate reading, warm your car up to its operating temperature. This temperature is typically between 195 and 220 degrees.  Your vehicle will be at its operating temperature when the reading on the coolant gauge on your car's dash is in the middle of the H and C markers. 

This reading shows that your car is adequately warmed up and will display an accurate reading on your transmission dipstick. If your vehicle is too hot or cold, the transmission fluid will not show a false-reading about your transmission's fluid levels. 

A car that driven at highway speeds on a hot summer day will be blazing-hot and will show that your vehicle has too much transmission fluid. A car driven on the highway will expand the transmission fluid levels greatly. You will need to cool down the car before checking the transmission fluid. 

A car that is too cold during the winter months will also show a false-reading that you are very low on transmission fluid. To combat this, warm your engine up for a few minutes until your car's engine is at operating temperature.

Do You Leave the Car Running when Adding Transmission Fluid?

Your car's engine should be running when you are adding new transmission fluid. A mechanic will place your vehicle on a flat level surface and turn on the vehicle. Once the vehicle has reached operating temperature, the mechanic will add fluid. You must put your vehicle in neutral and turn the handbrake is on as well. A car that moves without transmission fluid can lead to a costly repair bill. 

Since the transmission is not directly related to the engine, you can keep the car running and have no problems adding new transmission fluid. However, do not drive the vehicle if you do not have an adequate level of transmission fluid in the system. 

Should You Change or Add Transmission Fluid on Your Own?

A car's transmission is one of the most important and the most costly parts of a vehicle. If a mistake occurs when changing a car's transmission fluid, there will no longer be lubrication inside of the transmission. 

If a car's transmission does not have adequate lubrication, the metal inside will start to grind together and destroy itself. After enough time without transmission fluid, the transmission will be inoperable and need replacement.

An easy solution to preventing this problem is by taking your car to a professional. A mechanic's shop has changed, and added transmission fluid countless times. A professional will keep your car's transmission safe from mistakes that could potentially happen when inexperienced.  

How Often Do You Top Up Transmission Fluid?

Since transmission fluid is continuously reused within the system, your car should not be losing significant amounts of transmission fluid from your vehicle. Transmission fluid typically stays at close to the same level as you added and does not show signs of fluid loss. 

If you are experiencing a rapid loss of transmission fluid, you must take your car to a professional mechanic immediately. A car that is losing transmission fluid may have a significant leak that needs repair. 

Is it Better to Flush or Drain Transmission Fluid?

When performing maintenance on your car's transmission, you must understand the difference between a transmission fluid flush and drain. 

Transmission Fluid Drain

In a transmission fluid drain, the mechanic drops the car's transmission pan and drains the transmission fluid from the vehicle. However, not all the transmission fluid is removed in a transmission fluid drain.

Transmission fluid will still be inside of the torque converter and cooler lines of the transmission. While not all of the fluid will be replaced, this method is still useful. New transmission fluid added will replace the majority of the older transmission fluid.

Transmission Fluid Flush

In a transmission fluid flush, a mechanic removes all of the transmission fluid from the car's transmission system. This method is more effective when replacing your transmission fluid, but sometimes it isn't needed.

Depending on your model of car, you may have a sealed transmission. A sealed transmission makes the fluid flush not necessary and will be irrelevant to perform. Refer to your owner's manual before opting to do a complete transmission fluid flush. 


To ensure your car's transmission is healthy, you should check the transmission fluid on a routine basis. Once a month should be enough to catch any potential problems with your transmission system and signal, you need a fluid change soon.

Catching a transmission problem early can potentially save you from a large repair bill. 

When in doubt about if you should replace dirty transmission fluid or not, that's a sign it's time for a replacement. 

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