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Why Adding Too Much Transmission Fluid is A Bad Idea

Too Much Transmission Fluid

How excess transmission fluid damages your car and what you should do instead

Do you make it a habit to replace your transmission fluid regularly? Do you leave this task to the professionals, or would you like to go with the do it yourself approach? After all, it can save you the hassle of bringing your car into the shop, not to mention some serious bucks.

But, how do you even know the right way to do this, what kind of fluid you should use, and how much transmission fluid you’re supposed to add? In order to help you out, here is a comprehensive guide on what happens when you add too much transmission fluid, and what you should do instead.

What is transmission fluid?

First things first, let’s talk about what exactly transmission fluid is and what it does for your car. Transmission fluid is important in ensuring that your car runs smoothly. It lubricates and cools down the transmission so it doesn’t overheat and cause damage to your car.

There are different types of transmission fluids depending on the vehicle- or more specifically, the type of transmission that your vehicle uses. For example, newer car models often make use of transmissions that are controlled electronically.

What happens if you add too much transmission fluid?

Now that we have established the purpose and benefits of transmission fluid, you might be thinking that adding a little more shouldn’t hurt. More fluid means a smoother car, right? Wrong. Unfortunately, that’s not how it works.

Adding more than the recommended amount of transmission fluid is not advisable, since it can cause a variety of problems which can lead to long term and irreparable damage to your car. The excess pressure alone can lead to high friction which translates to a lot of issues, such as:

Automatic Transmission Fluid
  • An overall unstable vehicle
  • Premature wearing out of certain parts
  • Pushing out components like break parts and snap rings
  • Failure of the pressure valve
  • Transmission and engine damage
  • Erratic shifting
  • Oil starvation

What’s worse is that if the main issue of having an overflowing transmission fluid isn’t fixed, the situation can easily worsen as the car is used and driven, especially when you change gears, use reverse, and so on.

And, all the damage you will accrue won’t even be covered by your warranty, since overfilling your vehicle with transmission fluid is basically a human error caused by negligence and ignorance.

How do you know if there is excess transmission fluid?

One easily visible sign of an overfilled automatic transmission is foaming. This happens when the rotating gears of the engine cause splashing in the reservoir of fluid or oil, thereby resulting in excessive fluid temperatures and a failed transmission.

Meanwhile, if you have a manual transmission, you need to look out for fluid that is leaking from the vent, which is one major cause of erratic shifting, since the clutch becomes depressed. All of these things result in excess pressure of about 300 PSI or higher.

What to do when you add too much transmission fluid

There is a silver lining- if you’re lucky, your car’s transmission may be designed to be completely foolproof when it comes to overfilling it with transmission fluid. In such a case, it should be equipped with a hole to drain any excess fluid. But, this is not the case for many.

Don’t fret. There are plenty of easy fixes to help you address the problem. If your transmission doesn’t automatically drain excess fluid, you can simply do it manually. For this, you have several options that don’t involve going to the shop:

  • Buy a cheap extraction pump
  • Use a pump to siphon out the extra fluid
  • Remove the pan drain plug, if applicable
  • Take out the cooler line
  • Siphon the fluid out with your mouth and thumb

The last option isn’t really advisable unless you know what you’re doing. Not only is it somewhat dangerous, it also takes a much longer time for you to accomplish what you want to do.

Moreover, keep in mind that more often than not, you won’t be able to drain the exact amount of fluid for your transmission to be filled at the appropriate level, so be prepared to do a bit of topping off or replacing however much fluid is lacking.

How much transmission fluid should you add?

How much transmission fluid should you add?

To avoid the problem of adding too much fluid in the first place, it’s a must to know the right amount of transmission fluid that your car transmission needs. And, well, the answer depends on the transmission, and whether you are replacing the existing fluid or simply topping it up.

Most, if not all, transmissions need about 9 to 13 quarts of transmission fluid to fill it to the brim. If you’re replacing the existing transmission fluid and you know the size and type of your transmission, this process should be quite easy. Otherwise, you have to go about it carefully.

The right way to add transmission fluid

In order to avoid adding excess transmission fluid and risk damaging your vehicle, here is the right way to add transmission fluid:

  1. Pour half a quart of fluid at a time, and check the level on the dipstick. It might read as full especially if the engine is cool. Don’t worry about this.
  2. Start your engine and leave it to run for about five minutes or until it warms up considerably, then measure the level with the dipstick again.
  3. With the calibrated level in mind, pour half a quart of fluid again and measure. Do this repeatedly until the dipstick reads full.

You will know whether you have the right amount of transmission fluid in the transmission if the level on the dipstick reads at the upper level of the warm mark if the engine is warm, and the upper level of the cool mark if the engine is cool.

To keep things safe especially when the engine is warm, try to make sure that the measurement reads between two levels.

Should you replace your transmission fluid?

The short answer is yes. At one point or another, your transmission fluid will need replacing a few times over the course of your car’s lifespan. The only question is, when, and how do you know if it’s time to replace the fluid already?

Of course, you can always just check your user manual to see how often the fluid needs to be replaced as well as the right type of fluid you should use. For sealed transmissions, the fluid doesn’t need to be replaced as often, but you still need to get it inspected regularly.

How to know when it’s time to replace the transmission fluid

dipstick transmission fluid

That said, the best and most accurate way to know when to replace your transmission fluid is by checking the dipstick. This is because while car manufacturers have a standard recommendation, ultimately, the reality depends on how you drive and take care of your car.

The best indicator of the “health” of your transmission fluid is its color, and to a lesser extent, its thickness. The fluid on the dipstick should appear pink. Its viscosity should also be the same as motor oil.

Otherwise, if it’s brownish or black, then it needs replacing immediately. If it smells burnt, however, you will need to do more than replacing the transmission fluid, since that will just do more harm than good. At this point, you need to take your car to the shop and prepare for some expensive repairs.

For regular transmissions

You simply need to check the color of the dipstick. It should have a reddish or yellowish handle depending on whether you have a sealed transmission. Take it out and wipe it on a piece of white cloth or tissue to see its color.

For sealed transmissions

If you happen to have a sealed transmission, the process of checking your transmission fluid is considerably harder. You will need to check the level bolt or remove the bolt holding in the transmission fluid, and it can be difficult to do without the knowledge of a mechanic.

What happens if the transmission fluid is not replaced

While too much and not enough transmission fluid is problematic for your car and engine, an old transmission fluid is just as dangerous, if not even more so. The fluid itself may thicken and foam, burn, and wear out over time.

This occurs due to a variety of inevitable reasons, including friction between metal parts, dirt particles clogging drains and pathways, and temperature degradation. All of these things can cause a variety of serious issues, such as:

  • Loss of lubrication resulting in increased friction
  • Hardened seals leading to pressure loss and leaks
  • Foamed and burnt fluid creating engine problems
  • Damaged transmission that damages the gears, shifters, and valves


Your car’s transmission fluid plays an important part in keeping your vehicle running smoothly and without any problems, but it can also just as easily be the source of these problems if there is too much fluid, not enough fluid, or if the fluid is too old.

The good news is, it’s quite easy to assess and change your vehicle’s transmission fluid yourself, as long as you have the right tools and the right type of transmission fluid for your car, as well as knowing how much fluid to add.

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