Car owners will listen for any screeching noises their car makes, and pay attention to any changes in shifting gears, as both of these things could indicate problems in the transmission that could be caused by a deteriorated transmission fluid.
You must keep an eye on your car’s transmission fluid to change it at the right time and avoid these problems.
Although there is a consensus that the transmission fluid needs to be changed, different car manufacturers often issue schedules based on the model of the car.
The recommended distance for changing the transmission fluid is about 100,000 miles for most manufacturers, but this can be too long. Many mechanics would suggest changing every 50,000 miles for optimal maintenance.
While it is a simple task that you can do yourself, you should be careful not to overfill the transmission fluid as this could affect your gear change.
The basic working of a transmission
When we talk about the manual transmission, it is easy to understand how it works. A manual transmission is similar to an automatic transmission, but with some differences. The main difference is that manual transmissions are operated with a stick to change gears.
Inside the gearbox there are several gears of different sizes that are connected to the gear stick. Since everything here is operated manually, only lubrication is required to keep the gears inside the gearbox cool and smooth.
To achieve this, transmission oil is used – it is slightly different from engine oil, but serves more or less the same purpose.
However, the case of an automatic transmission is a little different. These transmissions also contain gears, but an additional component called a torque converter, which uses the transmission oil we are talking about.
Except that the transmission here relies entirely on the transmission fluid to function, and without that fluid the transmission would not function at all. The fluid for automatic transmissions is different from that for manual transmissions. Here the use of too much transmission fluid, even beyond the full mark, can have quite adverse effects.
Will it cause damage to my transmission if it’s overfilled?
Similar to the engine itself, transmissions generate a lot of heat which needs to be cooled. In vehicles with manual transmission this is achieved by using transmission oil, which we have talked about.
In automatic cars, the transmission oil serves two purposes, firstly as a coolant and lubricant, and secondly as fuel to make the transmission work.
While this fluid is essential for smooth operation, too much fluid in the gearbox can ruin the gearbox itself. This is because too much fluid in the gearbox would cause the gears to be completely immersed in the fluid, causing the fluid to foam.
Because of the foaming and the very small space for air, the excess transmission fluid would overheat the transmission instead of keeping it cool, and with no space for air, depressing the clutch would cause fluid to try to seep out of the transmission, compromising the seal.
This is even more dangerous in automatic vehicles.
Consequences of overfilling transmission fluid
As we have discussed, some major causes can occur if you have overfilled your transmission fluid. Some of the most common causes are listed below:
- Overheated transmission: Your transmission may overheat due to increased pressure and friction when you overfill your transmission fluid.
- Transmission oil leakage: If you top up too much fluid, high pressure will build up in the transmission, which may cause your transmission to leak fluid.
- Irregular shifting: Problems with pressure and shifting may cause problems with your vehicle, such as irregular shifting if you have overfilled your transmission.
- Foamed fluid: If you have overfilled your transmission, problems with the transmission may occur, such as foamed transmission fluid inside the transmission. See below for further explanation.
- Oil shortage: If your transmission fluid foams, it can stick to the top of the transmission and the gears and anywhere it should not be in the transmission. This can cause the transmission to jam if you are unlucky.
- Reduced fluid lubrication: As we have already discussed, transmission fluid can foam up, which greatly reduces lubrication. In the long run this can lead to heavy wear on your gearbox.
Since automatic transmissions rely on fluid to function, too much fluid in the transmission will result in irregular shifting. This can lead either to early shifting or to delayed shifting with jerking. The transmission can also make strange noises.
Too much fluid in the gearbox can also cause the oil itself to leak from the gearbox. The most critical thing about adding too much transmission fluid is that it causes a large pressure difference in the transmission itself.
A certain pressure is maintained inside the gearbox together with the fluid for which there is a limit indicated on the dipstick. Too much fluid will cause the pressure inside the gearbox to rise and you can imagine the damage the gearbox can cause.
Will a Slightly Overfilled Transmission get Damaged?
A slightly overfilled gearbox will not be damaged if quantities such as 0.3 litres/0.3 quarts are involved. If you overfill your transmission with one liter or more above the max mark, your transmission could be damaged.
Transmission fluid performs several functions in your vehicle. It is mainly used for lubrication, but it conditions your seals, controls the temperature of your transmission, and protects metal surfaces and moving parts from wear caused by friction.
Overfilling the transmission can affect the operation of your vehicle. It can cause leaks in the transmission seals, creating a puddle under the transmission.
You may have difficulty shifting gears and may overheat. These symptoms are caused by overfilling the transmission fluid and may cause serious damage to your vehicle.
If not corrected, too much transmission fluid can damage the seals and affect the consistency of the shifting process. Seals that prevent leakage when rotating shafts connect to solid components are very susceptible to too much fluid and could increase the risk of damage.
There will also be an increase in temperature in your gearbox as the foaming excess fluid does not take sufficient account of component friction.
How to know when your transmission fluid needs changing
The transmission fluid wears out over time, especially under heavy use. You will need to change your transmission fluid more quickly if you are towing trailers or heavy loads or if you make frequent stops, for example when driving in cities.
When driving with heavy loads, the operating temperature of the transmission increases, which can cause the oil to wear out more quickly. If the normally red or green transmission oil is darker and smells burnt, it must be changed.
If you experience slower or obstructed gear changes, this may be a result of the deteriorated transmission oil. It serves both as lubricating oil and as a hydraulic lift, which helps to make gear changes easier. The transmission oil also cools the transmission.
Reduced efficiency of these functions could be an indication that the transmission oil needs to be changed. You should also consider changing the transmission oil if it contains debris and foreign matter.
What do you need to consider before changing your transmission fluid?
The typical signs that indicate that your transmission fluid needs to be changed do not necessarily mean that you need to do so immediately. Unless you have a transmission failure, you can schedule a fluid change.
Before you make your decision, you must consider the manufacturer’s suggestion regarding mileage and take some time to find an affordable service provider.
Knowing the manufacturer’s specifications for your vehicle could also help you make the right choice between flushing and draining fluids during maintenance. You will also find information on compatible transmission oil options and all the steps involved in cleaning and maintaining other parts such as the filter.
So how much fluid should you add?
Transmission oil has some similarities with engine oil. Just as you would get a different reading from the engine oil dipstick when the engine is cold and when it is hot, you will get the same results when you check the transmission oil level.
However, there are two situations where the transmission oil can be checked. It can be checked both when the engine is hot and when it is cold. Here are some points to check the transmission oil:
- Park your car on a level surface.
- Pull out the dipstick
- Wipe the stick with a lint-free clean cloth and reinsert it
- Pull it out and check the fluid level
- If the engine is cold, check the cold mark
- If the engine is warm or still running, check the hot mark
- If, depending on the situation, the liquid level is too far below the markings, fill it up
As a rule, the transmission fluids do not have to be changed as often. Certainly not as often as engine oil. In the case of automatic transmission oil, the color of the oil should be fairly red or pink and the smell should not be reminiscent of burning. Similarly, in the case of manual transmissions, the fluid should not be dark, but pinkish red.
Did you know that replacing your transmission oil can be more cost-effective than a cumulative engine oil change? By finding the right oil and carrying out regular checks, you can ensure excellent preventive maintenance. If your transmission oil is old, discolored, or has a burnt smell, you may need to change it.
Lack of lubrication can cause damage to seals and other components, which can affect the life and function of your vehicle. It may also cause harder gear changes.
Following the owner’s handbook and manufacturer’s instructions for changing transmission fluid may help to protect your vehicle from total transmission failure. To avoid this costly problem, follow the procedure and fluid specifications provided.
If you change your transmission fluid manually, remember to take safety precautions. You should also monitor the quantity, as overfilling the transmission oil can affect your overall driving experience.
So if you have overfilled your transmission, it is an excellent idea to tap something through the plug or dipstick to get the correct level. Overfilled transmissions can cause serious damage to your transmission in the long run.
If you have further questions about transmissions, you can search for information on our website or leave your comment below, I will answer your questions as soon as possible.
Hi, I’m Magnus, the owner and the writer of Mechanic Base. I have been working with cars for 10 years, specialized in diagnostics and troubleshooting. I created this blog because I was tired of finding false information on the web while looking for repair information. I hope you enjoy my content!