“Should I change my transmission fluid yet?” If you’ve asked yourself this question, the answer will heavily depend on a lot of factors including how you use your vehicle, your car manufacturer’s recommendations, etc. Most likely, you’ve been told by fellow drivers that you need to replace your auto transmission fluid every 24,000 kilometers. Some may even tell you that it should be changed as often as 10,000 to 12,000 kilometers. To know the right answer, it can help to first know how your car’s transmission fluid works.

What does transmission fluid do?

Transmission fluid is a viscous liquid that lubricates, cleans and protects all the moving parts inside the transmission system. In automatic transmission vehicles, this fluid also acts as a coolant and mediator that delivers the engine’s power to the transmission. Different fluids for different fluid transmission systems can have different names. While automatic transmissions only have automatic transmission fluid, manual transmissions can use a wide variety of oils including:

  • Regular motor oil
  • Hypoid gear oil
  • Automatic transmission motor oil (in some cases)

If you would like to know which type of fluid to use for your car, you may refer to your vehicle owner’s manual.

Should you change your transmission fluid when it’s recommended?

Yes. However, it’s worth noting that the frequency at which this service should be done varies with each vehicle and manufacturer. For instance, the manufacturer recommendation for many automatic transmissions is to replace the fluid every 48,000 kilometers. That said, many mechanics think this interval is too long and recommend that fluid replacement should be done every 24,000 kilometers. Manual transmissions may follow a completely different schedule, so it’s best to stick to the recommended schedule in the owner’s manual.

What affects transmission fluid quality?

Certain driving habits that border on the severe, such as stop-and-go, long distance, or rough terrain driving, can cause the premature deterioration of transmission fluid, which in turn requires more frequent fluid changes. Some of the problems associated with dirty or deteriorated transmission fluid include:

  • Hard or rough shifting
  • Unusual noise or vibration emanating from the transmission
  • Gear slipping
  • Vehicle inexplicably surging forward
  • Delayed reaction when shifting

How exactly does transmission fluid deteriorate?

Extreme driving conditions such as the ones described above can raise the operating temperature of the transmission. This increase in heat is transferred to the fluid, and at hotter temperatures, the fluid won’t be able to perform some of its integral functions, such as cool the transmission.

With the transmission stressed, friction can start in the moving parts, and this in turn can lead to particles and shavings contaminating the transmission fluid, thereby affecting its performance. Left unattended, you may end up lubricating your transmission system’s moving parts with metal shavings and other contaminants, which will shorten the system’s life. The result can be an expensive transmission repair, or maybe even a replacement of the entire transmission system. Avoid this potentially debilitating financial setback by changing your transmission fluid at the right time.

How to check transmission fluid

If you do a lot of driving under extreme conditions, you should check the level and condition of the transmission fluid more often. You can do this by pulling out the transmission dipstick, which is located somewhere in your engine bay. Do this while the gearshift is in a ‘park’ or ‘neutral’ position. To check, wipe the dipstick clean, then re-insert it into the transmission and pull it out again.

If it reaches below the optimal level, then it’s time to take your vehicle to the service shop for transmission fluid replacement. Even if the level is okay, replace the fluid if it smells burnt or has particles in it. Occasionally, the fluid can become so contaminated with particles that the system will have to be flushed before the manufacturer’s specified period. Again, depending on your car, yours may say that the transmission fluid doesn’t need replacing at all. Even if the user’s manual says the transmission fluid will last the lifetime of the car, it’s still worth checking the level periodically, as leaks can still develop.

At the service shop

When you take your vehicle for a regular maintenance service, the technician in charge of your vehicle may suggest that a transmission fluid change or flush. Even if they can show you that the fluid has turned dark, this doesn’t necessarily mean that you need transmission fluid replacement, noting the valid reasons of replacement state above. Refer to the owner’s manual and see the manufacturer’s recommendations and take some time to decide. This will also give you the opportunity to price shop.

To flush or not to flush?

To speed up the process of transmission fluid replacement, some repair shops employ a flushing machine that forces the old fluid out and pumps the new one in. Although this saves plenty of time, some manufacturers advise against it. It is important to know the kind of fluid replacement method your car requires before you agree to a flush.

Certain car manufacturers call for the use of their own type of transmission fluid, and warn that using other types can be dangerous to the system. Likewise, specific types of transmission systems have filters that need to be cleaned or replaced along with fluid change. To make sure the correct transmission fluid and procedures are done to your vehicle, it’s best to have the work done at an authorized service center or dealership.

When was the last time you had your transmission fluid replaced?

If you’ve never had a transmission fluid replacement done and you have more than 100,000 kilometers on your odometer, should your change the fluid right away? The answer can depend on who you ask, with some technicians suggesting that it’s best to put it off until you encounter shifting problems. Some even reason that older transmissions are guaranteed to fail shortly because of the new fluid.

It can be hard to imagine that fresh transmission fluid can do harm to the system, so if it’s been a long time since your last fluid replacement, have the job done as soon as possible if you plan to keep your vehicle a few years longer. That said, if you are already encountering problems with your transmission, such as gear slipping or rough shifting, know that a simple transmission fluid replacement isn’t going to be the cure to your malady.