How To Check & Change Your Transmission Fluid

The transmission is an essential component of a vehicle. Inside it has many moving parts that need to be well lubricated to ensure a proper function and smooth operation.

Both manual and automatic transmissions are complex and can be very expensive to repair or replace. In this article, you are going to find useful tips to keep your transmission in good shape and to reduce the risk of breakdowns.

For a long time checking a vehicle’s transmission fluid level and condition was a task that could be easily performed by the end-users: you just had to find where the transmission oil dipstick was; once the dipstick was out you almost instantly knew if you had to top your transmission fluid or if you had to replace it.

Over the last decades, automakers started to introduce the “sealed transmission” concept. Some companies claim that their transmissions are “sealed for life”; and that they don’t need any kind of care during their lifetime. As these transmissions are “sealed”, they don’t have a dipstick, preventing the end users to check their transmission fluid.

As transmissions have been getting more complex; checking their fluid level is not as straightforward as it used to be. Modern parts are stronger and long-lasting thanks to the incorporation of new materials and production methods and there have been improvements in the oil quality, however, the transmission’s internal parts are still under heavy loads of heat and stress and the same goes for the lubricant inside. Normally in these transmissions, the oil level is not an issue but, what is very important is the transmission fluid condition.

When it comes to systems with so many moving parts inside, “maintenance-free” is a very optimistic term. Transmission oil is deteriorated by time and exposure to extreme temperatures and it also gets contaminated by debris generated by the transmission’s internal components wear.

This means that the transmission fluid becomes less efficient. Bad transmission fluid can damage the valves and solenoids of automatic transmissions and it may create obstructions that could lead to failures.

Taking care of your transmission

Checking the transmission fluid level in a car fitted with a dipstick it’s pretty easy and there are many articles about it that you can easily find on the Internet, that’s why we are going to focus on dipstick-less transmissions and everything you need to know to check their fluid level and condition.

Checking the fluid level

Some transmissions have filler-plugs and check-plugs, and most of them have a breather tube. It doesn’t seem that these transmissions are so sealed, right? What is a sure thing is that the designers of these transmissions don’t want end users manipulating them, that’s why some models use plugs with tamper-proof heads.

In most cases you can buy a proper tool at a specialized store, but if you aren’t a DIY fanatic, it’s better that you take your car to the shop to have your transmission’s fluid checked and/or changed.

Sealed transmissions, as the name suggests it, are meant to remain sealed, that’s why they shouldn’t need to have their fluid level checked. However, there are some symptoms that may be a sign that your transmission is running with low fluid: 

Signs Your Transmission Fluid Is Low

  • Your transmission is leaking. Being a sealed system it shouldn’t leak by any means.
    Most automatic transmissions have an oil pan, many of the time a defective gasket will fail to retain the transmission fluid inside. Manual transmissions tend to leak through broken seals or because of a damaged axle boot.  
  • You can hear buzzing, hissing or rattling noises coming out from your transmission.
  • On manual transmissions you can’t shift the gears smoothly and on automatic transmissions you may notice the transmission not shifting as fast as it should.
  • Transmission overheats.
  • Automatic transmission skipping gears or shifting gears roughly.
  • The check engine light is lit on your dashboard because of a transmission DTC.

Checking the transmission fluid condition

Take a look at your vehicle’s maintenance manual to see your transmission’s service schedule. In most cases, transmission fluid has to be changed every between 30 and 60 thousand miles, depending on the car’s manufacturer and transmission model.

Most automatic transmissions will also need to have a filter change.

If your manual says that your transmission doesn’t require any service, it’s advisable that you at least change the oil every between 50 and 80 thousand miles. Like we mentioned before, the transmission fluid doesn’t last forever and transmissions are very expensive to repair or replace. Changing your transmission fluid at reasonable intervals is the best way to ensure that your transmission fluid is clean and a good way to keep your transmission healthy.

Changing your transmission fluid

If you are experiencing any of the symptoms described above it’s always better to have your transmission fluid replaced. In that case or if you have reached the mileage where your transmission fluid has to be replaced, below you are going to find some guidelines based on the type of transmission of your car.

Manual Transmissions:

Check-plugs are generally on one of the transmissions’s sides or on top of them. It’s not so easy to check if your transmission needs a refill without the proper tools. You must read a workshop manual to be sure how to exactly check your transmission fluid.

Many transmissions don’t have check-plugs. The only way to measure the oil level of these transmissions is to remove it to a clean pan or container and see how much oil goes out. You don’t need to warm up your car to do it, you just can do it at room temperature.

Changing your manual transmission oil is pretty simple:

1 – Jack and level your car. If you don’t have access to a car lift, you can use some car trestlers to do the job.

2 – Locate the drain plug and place a container under it to catch the oil that it’s going to drip from the transmission.

3 – If your car has a filler plug, it’s better to unscrew it to allow the old oil to leave the gearbox more easily. Remove the drain plug as well and let the oil drain.

4- Refit the drain plug. Don’t overtight it to avoid damaging the plug or the thread.

5 – Fill your transmission with the amount of oil specified by the service manual. If your car doesn’t have a filler-plug you will have to fill it by the breather tube.

6 – Refit the filler plug if you have removed it.

7 – Dispose the used oil properly.

Automatic Transmissions

Changing the oil of an automatic transmission can be a complex task. Having a good scan tool is becoming more and more essential. These kind of transmissions need to be kept at a certain temperature to measure their fluid level, unlike the manual transmissions, the oil needs to be warmed up and remain at a certain temperature within a margin of around 50° Fahrenheit or 10° Celsius.

Many automatic transmissions need to have the oil fluid filter replaced when the fluid is changed. Some have internal filters, others external filters and most of them have both. In some cases you need to have both replaced and in others the internal filter is changed only when the transmission needs to be open for repair.

My advice is that you take your car to a specialist to have your automatic transmission fluid change. But if you like to work on your car, you need to make sure what your transmission model is and get a good service manual. There are also a lot of good tutorials on YouTube. Some pointers: if you decide to go that way: you have to know and be very sure about what transmission fluid your transmission uses and how much fluid you are going to need.

You also have to be aware that if servicing your transmission requires removing its oil pan, always replace the gasket. There are shops that sell “service kits” that bring everything that you need to get the job done. Try to have everything you are going to need before starting to do the job.

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