You may be wondering if changing the transmission fluid is safe. So, the quick answer is both yes and no. In some circumstances, changing the transmission fluid can be beneficial, but it can also be harmful. 

There are a few things to keep in mind, which we will go over further in this article. First, let us look at why changing transmission fluid is important.

Why is changing transmission fluid important?

Transmission fluid is critical for providing proper lubrication to transmission parts. Grit and grime can cause your transmission fluid to deteriorate over time, making the fluid flow in the moving parts difficult. Transmission fluid that is old or contaminated can cause whining noises, slipping gears, and heating issues. Since transmission fluids do not evaporate or dry up like engine oil, changing them is your only option.

Transmission fluid should be changed every 50,000 to 100,000 miles as it gets clogged. If done correctly, changing the transmission fluid has no negative consequences. Let us examine the circumstances under which changing the transmission fluid can result in damage.

When should you not replace transmission fluid?

Before deciding whether changing the transmission fluid will be good or bad for your car, you should ask yourself a few questions.

  • Is your car new or old?
  • How well is your transmission system maintained?
  • Does your car have automatic or manual transmissions?
  • Do you own a high or low-mileage car?

Based on the above questions, whether transmission fluid needs to be changed should be decided. Two choices are to flush the old fluid or change the transmission fluid.

When should the transmission fluid be changed?

This depends on how well you’ve kept up with your car’s transmission system. Even after changing the fluid, nearly half of the old transmission fluid will still be mixed with the new. 50% of the old fluid will remain after changing the fluid, whereas 100% of the old transmission fluid will be removed after flushing.

Grit and grime can build up in the fluid if the gearbox or another transmission component is not properly maintained. In this situation, flushing out all the fluid might result in the clogged fluid remaining in the transmission system’s channels. Therefore, changing the fluid is advised over flushing if the car is new or the transmission system is not well-maintained.

When should the transmission fluid be flushed?

Flushing the fluid will clear all the particles of old transmission fluid from the container. Typically, it is advised to flush the transmission fluid if you own an old or a lower-mileage car. Also, it is advised that the transmission system is maintained properly if you want to flush out the fluid.

This is due to the old fluid’s gradual clogging with outside debris if the transmission system is poorly maintained. This clogged fluid can build up as sludge in the transmission system when you flush out the old fluid.

Flushing the fluid will be a better option for the old and lower-mileage car if you are certain the transmission system is properly maintained. It is also advised to flush out the oil in automatic transmissions and vehicles because the pressure from the thick oil can harm the clutches. Check the transmission fluid level properly to know exactly what the issue is.

FAQ’s on Can Changing Transmission Fluids be Bad

Oil changes and flushing each have advantages over the other. To make sure there is no remaining old oil, flush the system before adding new transmission fluid. However, this may result in transmission slipping and the leftover collection of old transmission fluid.

If you change the transmission fluid, the old fluid will still be present ( around 50%) and mixed with the new fluid.

The type of transmission system your car has will determine this. While automatic transmissions can go up to 100,000 miles, manual transmission fluid can last for as little as 30,000 to 60,000 miles.


It is crucial to make sure the transmission system is functioning properly. The transmission fluid for that vehicle needs to be changed regularly. However, flushing the transmission fluid will do more harm than good if it is poorly maintained. 

Although some old oil will remain in the container, changing the transmission fluid is preferable if the car is new and the transmission is poorly maintained. Therefore, it is advised that you keep the transmission system in good condition by performing routine fluid changes and maintaining proper cooling.

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