a blog entry by Philipp Janczewski

March 23 , 2022
3 minutes read

A regular transmission oil check is crucial for the performance of your vehicle. An understanding of why to check transmission oil and maintain adequate levels of the fluid can extend your vehicle’s life. In this blog, we will help you understand everything from A to Z of transmission fluid check and the possible signs of a low transmission fluid level.

Facts about transmission oil

Healthy gearbox through clean oil

Today I'm shedding a little light on the subject of transmission oil checks. If you know what to look for, the transmission oil can tell you a lot about a vehicle and possible damage. To assess the condition of the gearbox oil, it makes sense to take an oil sample. This way I can get an idea of the condition of the gearbox.

In my new video, I take you to the workshop and show you gear oils in various states. You want to know how you can recognise a damaged gearbox or a defective radiator? I'll tell you in the video, so watch it.

Benefits of regular transmission oil checks

To function properly, a transmission needs sufficient lubrication. This minimizes wear and tear and optimizes efficiency. So, transmission fluids play a vital role in keeping your gearbox from failures. Save yourself the major expense of a transmission exchange and check transmission fluid regularly. Maintaining your transmission fluid level is a must for a better performance.

Preventing Costly Repairs

In addition to the intervals for checking or changing the transmission oil specified in the vehicle’s maintenance instructions, it can therefore make sense to check the oil level in shorter intervals. Especially when regularly traveling with a trailer or caravan, or if the transmission is subject to other heavy loads. This helps to prevent costly repairs.

Prolonging Transmission Lifespan

Regular transmission oil checks will help to get rid of contaminated and dirty fluid that does not provide power and lubrication to your car’s transmission. This helps prevent transmission problems and extends the transmission's lifespan.

Signs of low transmission oil

Here is how to detect the signs of low transmission oil:

Recognising Symptoms

Similar to other gradual signs of wear on a vehicle, such as worn shock absorbers, a fluid level in the transmission that is too low is difficult for the driver to detect. Nevertheless, symptoms such as grinding or vibrating when shifting gears, slow or jerky shifting of gears in Automatic Transmissions, and weak acceleration may be a hint. At the latest when symptoms like this occur, attention must be given to the gearbox.

Understanding the Risks

In general, all fluid levels in a vehicle that are too low will sooner or later lead to premature wear or even failure of the system in question. The same applies to vehicle transmissions! Low transmission oil levels can result in excessive friction, which will eventually lead to overheating. It will also impact the performance of your car and make your driving tedious and dangerous.

How to check transmission oil

You can ensure optimum transmission maintenance with the right tips and tricks. Let us begin by showing you how to check the transmission oil of the vehicle.

Gather Your Tools and the Vehicle Manufacturers Guidelines

To check and if necessary, top up the fluid level, it is vital to have the guidelines of the vehicle manufacturer on hands! The procedure for checking the fluid level as well as the transmission fluid to be used are described therein. An oil collection pan and the appropriate safety equipment should of course be available.

Warm Up the Engine

To reliably check the level and condition of the transmission fluid, the transmission usually has to be brought to its operating temperature. So first carry out a test drive. You may already be able to see the first signs of a low oil level or even a transmission failure.

Manual or Automatic Gearbox

When it comes to checking the transmission oil, automatic and manual transmissions differ from each other. While the oil level in manual transmissions can only be checked directly on the transmission block - i.e. only when the vehicle is raised, some automatic transmissions may have an oil dipstick, similar to the dipstick for checking engine oil.

Park on a Level Surface

For both types of transmission and the correct procedure when checking the oil, it is important that the vehicle is on a level surface. In this respect, checking the oil level in the transmission is no different from checking the engine oil.

Interpret the Oil Level

Note: On many modern cars, the transmission fluid level can only be checked via the vehicle diagnostic system!

Manual gearbox: Raise the vehicle and locate the fluid-check-screw. It is usually located on the side of the gearbox block. At this point we would like to refer once again to the information provided by the vehicle manufacturer! Unscrew the screw from the gearbox. Attention: Hot transmission fluid may leak! Normally the correct level is given when a small amount of fluid leaks out of the hole after removing the screw.

Automatic gearbox: On some Automatic Transmissions the oil check can be similar to the procedure on Manual Transmissions. On others open the hood and look for the transmission fluid dipstick and pull it out. At this point we would like to refer once again to the information provided by the vehicle manufacturer! Use a lint-free cloth to wipe and clean the dipstick. Re-insert it into the transmission fluid and see if it reaches the "full" line or is within the hash marks at the dipstick.

Adding Oil

If you come to the conclusion that the oil level in the gearbox is to low, the following things should be checked before topping up: Does the amount of missing oil suggest that this is a normal loss during the running time, or is there perhaps another reason for the oil loss? A rough thumb rule:

If you have to add more than 25% of the required volume or if the transmission oil level is often too low during a check, further diagnostic steps are necessary. If so – check the transmission for leaks!

If there is no error, the missing transmission fluid can be filled in. It is essential to follow the vehicle manufacturer's instructions on the correct transmission oil! Make sure to avoid overfilling as it will inhibit proper lubrication and it is difficult to remove excess fluid out of the gearbox.

Tips for a healthy transmission

Here are a few tips for maintaining and properly handling your vehicle's transmission:

Drive Smoothly and Avoid Overloading

Any bad driving practices, such as permanent excessive accelerating or decelerating, or shifting the gears violently, can lead to system damage and decrease the lifespan of your vehicle’s transmission. Additionally, you must refrain from towing trailers or caravans beyond your car’s capacity, as this can strain the transmission. This can also lead to system overheating, which can result in irreversible damage. Simply don’t put excessive weight on your transmission to prevent any possible malfunctions.

Regular Checks Beyond Oil

You must check fluid levels regularly to ensure that they are at optimal levels and the transmission is in good condition. Excessively low levels can be a sign of fluid leaks. You must also examine the fluid colour for added precautions. If needed, you must visit a professional mechanic to get your transmission fluid checked or changed.

About the author

Phillip Janczewski

Philipp Janczewski

Philipp is Global Head of Training Development, working with ZF Aftermarket since 2013. His motto as #zfexpert:

“You can never have too many horses! No matter in which engine.”