6 Causes of Transmission Fluid Leaks (& Repair Cost)

What could be the reason why transmission fluid is leaking from my transmission and how much will it cost to fix it? Read on!

Causes Of Transmission Fluid Leaks

Did you notice a fluid leak on your driveway, which seems to come from the automatic transmission, or are you just tired of refilling the transmission fluid?

Then it is definitely time to repair your transmission fluid leak. Repairing transmission fluid leaks does not have to be very expensive, and in most cases, it will be surprisingly easy.

In this article, we will discuss the most common causes of a transmission fluid leak and how much it costs to repair it. First, let’s take a look at the most common causes:

The most common reason for transmission fluid leaks is a bad transmission pan gasket or a rusty transmission pan. If you or your mechanic didn’t tighten the drain plug properly the last time, it may also be the cause. It can also come from a leaky seal on the transmission.

Here is a more detailed list of the most common causes of a transmission fluid leak.

6 Common Transmission Fluid Leak Causes

1. Bad Transmission Pan Gasket

Transmission Gasket Leak

A leaking fuel pan gasket is the most common cause of a leaking automatic transmission. The gasket should be replaced every time the transmission pan is removed on most car models, but many people install the old one again. This can lead to leaks very soon.

It also happens that they get old and start leaking because the transmission fluid is slowly eating them.

Some car transmission models use a sealer instead of a gasket, which can also get worn and need a replacement.

2. Cracked or Rusty Transmission Pan

Transmission Pan Removal

Another common cause of a leaking transmission is a cracked transmission pan. A cracked transmission pan do usually happens if your transmission has an aluminum transmission pan. This can happen if you, for example, hit a hard object under your car on the transmission pan while driving.

Rust is a problem if you have a steel transmission pan. The pans are pretty thin material-wise, and if they start to rust, it will create a hole pretty fast. Check for any signs of rust, and if you find any, it is probably time to replace the pan.

3. Leaking Transmission Pan Drain Plug

Transmission Fluid Drain

Not all automatic transmission has a drain plug, but some do, and if you have one on your transmission, it is likely leaking. You usually find an O-ring sealing on the drain plug, which should be replaced after each fluid replacement.

Most people do not replace this O-ring sealing when they change the fluid, resulting in a leaking transmission after a while.

4. Bent Transmission Pan

Transmission Fluid Removal

If someone before you replaced the transmission fluid and had problems removing the pan because of strong sealant, for example, the pan might be bent around the edge.

The steel transmission pans are pretty weak, and if someone took a big screwdriver to remove it, there is a risk that they bent it. Check for any damages around the edges of the transmission pan. If it is bent, you maybe have to replace the transmission pan completely.

5. Transmission Fluid Pipe

Transmission Line Leak

A not of automatic transmissions do also have fluid cooling – not all of them, though. If you have a cooled automatic transmission, you will most likely have fluid lines going to the transmission cooler in the front of the car.

These lines are made of steel and tend to get rust holes and start to leak. They are also going very near the pan often, so you might think it is a leak from the pan but is coming from the transmission line above.

6. Clogged Transmission Ventilation

Transmission Pan Removed

Most automatic transmissions have some type of open transmission ventilation on top of the transmission to ensure it will not build too much pressure inside of it. These small transmission ventilations can get clogged on some car models, which will create transmission leaks everywhere.

Look at the top for your transmission of some ventilation hoses, or ask your authorized dealer if your transmission has ventilation. Because they are installed on the top of the transmission, they can be difficult to reach.

Transmission Fluid Leak Repair Cost

The average transmission fluid leak cost is between $100 and $300, depending on the car model and labor costs. You can expect $50 to $150 in parts and the rest in labor costs.

Here are some examples of repairs that could fix a fluid leak cost. The prices include parts, new fluids, and labor work. The prices can differ heavily depending on your transmission model, but it gives you a clue.

Type of workPrice
Transmission Gasket Replacement Cost (Including Fluid & Filter)$150 to $400
Transmission Pan Replacement (Including Fluid & Filter)$250 to $500
Transmission Pan Drain Plug Replacement$20 to $50
Transmission Fluid Line Replacement$50 to $200

Is It Safe To Drive With A Transmission Fluid Leak?

If you are sure that the transmission fluid level is good, you won’t damage your transmission with a small leak. The best practice is to repair the leak as fast as possible, though.

The more you drive a car that is leaking fluid, the more the fluid gets drained. At some point, you will not have any left, and your transmission will get damaged. If the leak is small, it can buy you time to dash to the nearest service station for repairs.

Of course, it is terrible for the environment to have a transmission fluid leak, so it should be repaired as fast as possible.

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Written by:

Magnus is the owner and main author of MechanicBase. He has been working as a mechanic for over 10 years, and the majority of them specialized in advanced diagnostics and troubleshooting. Certified Automotive Diagnostic Technician.