How to check transmission fluid in manual or auto, and change it

We outline how to check transmission fluid in manual or automatic cars, and change it if it is needed.

The transmission is one of the most complex and at the same time one of the most important components in a car. It sits between the engine and the drive train and has the task of metering the torque generated and transmitting it to the wheels. The special thing about the gearbox is its structure. It consists of many large and small gears that mesh precisely with one another.

Manufacturers use transmission fluid to minimize mechanical friction and prevent the proverbial sand from getting into the gearbox. But is transmission oil durable enough to last the life of a car? And how do you check it and change it if needed? If this is your first time, read how to get first-time DIY car servicing right.

Change fluid or just top up? And when?

Transmission fluid is not changed as often as engine oil. While the latter should be renewed every one to two years, new transmission fluid is usually only added once in the vehicle’s life. Contrary to popular belief, this recommendation does not only apply to vehicles with a classic gear shift. Even if you have an automatic vehicle, you should think about changing your transmission fluid after a few years. Also useful is knowing How to test a relay, with a step by step guide to check and replace relays

Some manufacturers recommend changing the transmission oil after 150,000 to 180,000 kilometers. Many car workshops recommend changing the gear oil after 50,000 to 100,000. Whether or not it makes sense to change the transmission oil is primarily determined by how the car is used.

If the car is mainly used on short journeys with many gear changes, an oil change is recommended after 100,000 kilometers at the latest. The type of transmission (automatic or manual transmission) does not matter when it comes to the change.

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Poor quality or low transmission fluid?

Over time, all oils lose their viscosity and their ability to lubricate mechanical parts deteriorates. In the case of gear oil, this can be noticeable as follows:

• With manual transmissions: engaging the first gears is jerky and difficult. The problem is more pronounced with cold starts.
• The gears change with a time delay. After engaging a higher gear, it takes time for the transmission to respond.

In both cases, it is advisable to check the transmission fluid. It is also advisable to check the oil level if oil stains appear under the vehicle. An indication of insufficient or insufficient transmission oil can also be if there are jerking movements while driving or if the fuel consumption increases for no apparent reason. In the worst case, continuous driving with used or insufficient transmission oil can result in transmission damage.

In summary: signs of bad transmission fluid

The following signs indicate that there is not enough fluid in the transmission or that it is time to replace it:

• Extraneous noises and vibrations when switching;
• switching problems can occur in winter if the part has not yet warmed up;
• in vehicles with automatic transmission, the dynamics can deteriorate;
• jerky switching;
• delayed switching operations;
• an automatic transmission shifts up or down when it shouldn’t.

How to check transmission fluid in manual or auto

Preparation

The quality of the fluid and its level can be checked visually. However, the effort required for how to check for transmission fluid in automatic and manual transmissions is different.

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How to check transmission fluid in manual vehicles

With manual transmissions, since the gearbox is in the middle under the car, the vehicle has to be on a lifting platform. A jack is not enough for this. After removing the gearbox cover, you will find an oil filler plug on the side of the gearbox. After unscrewing it, insert a wire into the hole to check the level. A special tool (a syringe) is required to refill the transmission fluid with manual transmissions.

• Prepare all the necessary tools and chemicals: a wrench, WD-40, and a metal brush, as well as clean towels or paper towels. You may also need fluid, however, and be careful: you should use what is currently in the transmission. Information about the fluid used in your model should be given in the vehicle manual. If this is not the case, however, seek professional help.
• Put your car on a lift or over an inspection pit. Unless you have such equipment and your vehicle is front-wheel drive, remove the left front wheel to gain access to the inspection window on the transmission case.
• Now apply the parking brake.
• If you have just switched off the engine, wait a few minutes for the oil to drain into the oil pan.
• Use a metal brush to clean the fuel cap and the area around the fuel cap. Wipe with a clean cloth and then with solvent. This will prevent dirt from getting inside the device.

How to check transmission fluid in automatic vehicles

With automatic transmissions, you can usually check the level using a dipstick in the engine compartment and top up with oil if necessary. To do this, you should first warm up the engine, switch off the car and shift through all gears again. Then park the vehicle with the engine running and check the fluid level (please note any deviating recommendations in the operating instructions!). But be careful: you must not use just any fluid when refilling! The fluid must match your vehicle and the fluid already in the transmission. It is best to ask your dealer or a car workshop.

Automatic transmissions usually have dipstick to check the level of the automatic transmission fluid (ATF). The procedure is as follows:

• Park your vehicle on a level surface.
• Open the hood.
• Find the gear oil dipstick. Usually the handle is light in color, often orange. Information on the position of the dipstick can be found in the vehicle manual, if necessary.
• Start the engine. Let it run for a while to warm up.
• If you do not perform the test immediately after riding, cycle through all modes and hold the lever in each position for about three seconds. This helps distribute the gear oil along the channels.
• Depending on the vehicle model, switch the lever to the “Park” or “Neutral” position. The exact position is often indicated on the dipstick.
• Apply the parking brake.
• Refer to the vehicle manual to determine whether the engine must be running or switched off for the check. With some Acura and Honda models in particular, the engine must be switched off here after warming up.
• First remove the dipstick from the gearbox and then wipe it with a clean, lint-free cloth.
• Insert the dipstick all the way and then remove it.
• Look at the dipstick. You will see two marks on it. One shows the transmission oil level when the engine is cold and the second when the engine is warm. They usually have corresponding markings: either “cold” and “warm” or the numbers that indicate the temperature. Since that engine should now be warm, the oil trace on the dipstick must also be at the “warm” mark or a higher temperature, but not above. It is not recommended to measure the transmission fluid level when the engine is cold as the results will be inaccurate.
• If necessary, top up the ATF in the gearbox. To do this, turn off the engine and use a funnel.
• Wait for the oil to flow down into the oil pan.
• Finally, restart the engine and then also check the transmission oil level again.

Some models, such as the BMW E46, BMW E39, as well as the Audi A4, Audi A6 or the Volkswagen Passat, are equipped with gearboxes without a dipstick.To check whether the fluid level is sufficient here, proceed as follows:

• Warm up the transmission to operating temperature by covering a distance of about 15 kilometers.
• Now place the vehicle on a lifting platform, an inspection pit or a ramp to reach the underbody.
• Start the engine.
• Switch to the appropriate mode – “Park” or “Neutral”.
• Unscrew the inspection plug at the lower end of the gearbox. If the liquid leaks out of the hole, there is no need to refill it. Screw the cap back on.
• If nothing leaks here, it will mean there isn’t enough oil.
• Use a special pump or a hose and funnel to pour some ATF through the filler opening until it comes out of the inspection hole.
• Close the hole again with the lid.
• Start the engine.
• Unscrew the lid and repeat the process with refilling.
• As soon as the ATF drains again, close the hole.
• Now switch the gear selector switch through all driving modes.
• Open the inspection opening and add liquid for the last time.
• Unscrew both the inspection and filler caps.
• Wipe the streaks off the gearbox.

How to change transmission fluid

Changing the transmission fluid is not an easy undertaking and not recommended for laypeople. If you still feel confident about replacing the fluid, here are some tips for you.

For a car with a manual gearbox

To change the transmission fluid in a manual transmission, proceed as follows:
First, find out how much of the transmission fluid your gearbox can hold here. You can find this information in the vehicle manual. In addition to the required amount of liquid, depending on the version of the vehicle, you also need the seal for the transmission pan or an O-ring for the drain screw, some sealant, a container to collect used fluid, a funnel and hose or a syringe, as well as a cloth and a wrench to loosen the fastenings.

• Before starting, you should drive 5-10 km so that the fluid warms up and becomes less viscous: it will be easier to drain it then.
• Put your car on a lift, inspection pit, or ramp. If necessary, secure the wheels with wheel chocks.
• Put your car on a lift
• Remove the sliding plate.
• Place a container under the oil pan
• Remove the drain plug (for example on the Renault Megane, as well as the Audi 100 and Audi A6) and then also let the transmission fluid drain out. If there is no drain plug here (such as in the Opel Astra or Chevrolet Lacetti), simply loosen the fastenings of the oil pan, wait until the oil comes out and then remove the component by tilting it to the side very carefully .
• Then drain the transmission fluid as well
• Use a brake cleaner to remove the dirt from the mounting seat of the oil pan or plug threads.
• Use a brake cleaner to remove the dirt from the mounting seat of the oil pan or plug threads
• If you have removed that oil pan during work, also clean the surfaces of any residues of the old seal, then wipe it off with solvent and insert a new seal with a sealant. Now put that oil pan back in place.
• Install a new gasket with a sealant
• If you have removed the plug, also replace the O-ring and use it to close the drain opening.
• Use a hose and funnel to add the required amount of fluid to the gearbox. You can also fill them with a syringe through the inspection port.
• Reassemble everything in reverse order.

For a car with an automatic transmission

It is not easy to change the transmission fluid in a car with an automatic transmission. When the fluid is drained, a residue always remains in the gearbox. It is therefore better to have the automatic transmission flushed in a specialist workshop. This process is also possible with manual transmissions and can increase their service life. However, it is also more expensive than just changing the transmission fluid.

Conclusion

Replacing the transmission fluid and refilling it in good time help to significantly extend the service life of both manual and automatic transmissions and to ensure long and stable operation. Follow our advice and you will be able to check the oil level and quality yourself so you can decide exactly what to do next here.