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Your car’s transmission relies on good quality fluid for optimal operation. It is the equivalent of the motor oil for your engine. It lubricates the different metal parts of the transmission so that they will not overheat. This helps keep the transmission in good working order. Unfortunately, there are some car owners who do not realize the consequences of putting too much transmission fluid in their cars. Let us look at the possible effects of overfilled transmission fluid and its signs.

What are the Consequences of Overfilling Your Transmission?

Vehicle manufacturers have very specific recommendations as to the amount of automotive fluids that should go into the different parts of their car. From engine oils to brake fluids, engine coolants, and transmission fluids, automotive engineers have determined these levels to ensure the correct functioning of the different parts.

Transmission fluid is like engine oil. It must be of the right viscosity so that it can circulate through the different components of the transmission. It should also be the right amount. This helps ensure that all of the surfaces in the transmission are lubricated. It is this lubrication that is the principal function of the transmission fluid.

As the fluid lubricates the metal surfaces, it prevents friction. This also prevents unnecessary wear, while also preventing the premature breakdown of these parts. What many do not realize is that the correct amount of fluid in the transmission also corresponds to the correct levels of pressure.

Fluid will exert a pressure against the surface that it is in contact with. When the right amount of fluid is used, one can feel more confident about having the correct amount of pressure within the system. It is for this reason that the principal effects of having too much fluid in the transmission are always related to a buildup of pressure.

So, what happens if you overfill transmission fluid? There are three fundamental effects.

Increased Transmission Fluid Pressure

As mentioned, filling your transmission with more fluid than necessary can also increase the pressure within the automotive component. An unfortunate consequence of increased transmission fluid pressure is air contamination.

This occurs because the rotating gears of the transmission splash the fluid within the chamber. It causes a chemical reaction that leads to the formation of air bubbles or foam. The presence of air bubbles in the transmission fluid can affect the fluid’s lubricating function. To be more specific, it affects the overall viscosity of the transmission fluid.

Instead of delivering a thin layer of oil in between metal parts, pockets of air are delivered. Some of the gears of the transmission don’t get lubricated at all. This makes the metal parts to grind against each other.

Grinding can lead to the premature wear of the gears. It can make shifting a lot more difficult. You may have a transmission that will be very sluggish in shifting. The car will feel slow or unresponsive.

Overheating Transmission

The inadequate lubrication of the gearbox can also lead to overheating. Keep in mind that one of the essential functions of the transmission fluid is to keep the transmission from heating up. It does this by eliminating the friction that can occur between two adjacent metal surfaces.

While overheating may not have an immediate effect on the gears of the transmission, it can lead to the breakdown of the seals. This safeguards the transmission by keeping the fluid within the system. When they do break down, these seals are no longer able to keep the transmission fluid within the gearbox.

An overfilled transmission fluid can lead to the leakage of the fluid from the gearbox. This further robs the transmission of critical fluid. This can lead to a loss of ability to shift the transmission while driving. It may not go into any of the drive gears anymore.

Transmission Failure

The combination of increased fluid pressure, leaking seals, and metal grinding parts can lead to the faster breakdown of the transmission. The increased fluid pressure can exert its toll on both the gearbox and the transmission lines.

If the car owner ignores the different signs of having too much transmission fluid, there is a chance that the transmission will fail. You can go for a rebuild, which can cost you from several hundreds of dollars. However, in complete transmission failure, you might as well get a replacement transmission.

Hand pouring transmission fluid

What Signs or Symptoms will Indicate an Overfilled Transmission?

We now know what happens if you overfill transmission fluid. The other thing that car owners would also like to know is if there are ways we can tell if we put more transmission fluid than necessary. Here are some of the things that can help you determine if you overfilled your transmission or not.

  • “Overfilled” Dipstick

While not a reliable method, using the dipstick is one of the easiest ways you can determine if you have too much fluid in your gearbox. You only need to pull out the transmission fluid dipstick from its port and check the level of the fluid near the tip. Unfortunately, there are many factors that can make the interpretation of the fluid levels very inaccurate.

The fluid has a very liquid consistency when the transmission is running or is at its optimal operating temperature. The same fluid turns thick with a drop in temperature. It is for this reason that checking the level of the transmission fluid using the dipstick method should be done only after running the engine for at least 5 minutes.

There is also the issue of fluid present in the inner walls of the transmission dipstick port. Some of them can stick to the surface of the dipstick and give you an inaccurate reading.

  • Problems in Shifting

There are many reasons why your transmission may not be shifting as smoothly as it should. It could be because of low levels of transmission fluid. This can also be brought about by having too much transmission fluid.

As we already learned, overfilling your transmission can increase fluid pressure and lead to the creation of foam. This undermines the lubricating properties of the fluid. The resulting transmission overheating can lead to a breakdown of the seals, causing the fluid to leak. Problems in the torque converter, worn-out gears, and issues in the solenoid can also bring about problems in shifting.

You may also notice a significant delay in shifting. This is again related to the insufficient lubrication of the gears. The transmission will have to wait for these unlubricated parts to engage before shifting the gear.

  • Leaking Transmission Fluid

One of the telltale signs of an overfilled transmission fluid is the presence of a puddle underneath the transmission. The fluid often has a reddish color. This will help differentiate it from other types of automotive leaks. Transmission fluid that has never been replaced will have an orange color. Some can also have a pinkish color.

Leaks occur because of damage to the transmission seals. Their breakdown is due to the loss of lubrication. It can be secondary to the formation of foam and the increase in transmission fluid pressure. Of course, there are other possible explanations as to why you see transmission fluid leaks in your car.

  • Transmission Whining, Humming, or Grinding

This is one of the most difficult to diagnose because of the transmission’s proximity to the engine. Noise coming from the motor is often louder than those coming from the transmission. As such, it is not surprising why many vehicle owners miss this sign of excessive transmission fluid.

Whining in the transmission is almost always an indication of a problem in the transmission fluid pump. Low-frequency hums can also signal excess transmission fluid. Grinding noise can often mean that the transmission gears are already rubbing against each other.

How Much Transmission Fluid Should You Put in Your Car?

Excess transmission fluid is not good for your car. The question now is how much transmission fluid you should put in the gearbox. Your owner’s manual holds the answer to this question. Vehicle manufacturers provide the specific amount of fluids that goes into each component of the car. These can include the engine and the transmission fluid.

In instances where such information is not available in the manual, you can still fill your transmission with the correct amount of fluid.

You can remove the excess transmission fluid or replace it. There are some people who do not recommend replacing the transmission fluid, especially in high mileage vehicles. However, the quality of the fluid deteriorates over time. It is better to replace your old transmission fluid with a new one.

You can siphon the fluid from your transmission. An alternative will be to drain the fluid from its pan at the bottom of the transmission. You can then measure the drained fluid to have an idea of how much transmission fluid you will have to put in your car.

If you measured 4 quarts, then it would be best to start filling your transmission up to 3.5 quarts. Turn on the engine and bring it to normal operating temperatures before you check the dipstick. Slowly add transmission fluid until you get to the optimum level on the dipstick.

Using too much transmission fluid in your car can damage your transmission in the long run. The formation of foam can undermine the ability of the fluid to protect your transmission.

Sources:

  1. Transmission Fluid Service at your home or office – Your Mechanic
  2. How to Change Transmission Fluid – Wiki How

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