6 Causes of Transmission Fluid Leaks (and Repair Cost)

Have you noticed a fluid leak in your driveway that appears to be coming from the automatic transmission, or are you just tired of refilling transmission fluid?

Then it is definitely time to repair the transmission fluid leak. Repairing transmission fluid leaks doesn’t 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 the cost of repairing it. Let’s first look at the most common causes:

The most common reason for transmission fluid leaks is a bad transmission pan gasket or a rusted transmission pan. If you or your mechanic didn’t tighten the drain plug properly last time, that may also be the cause. It could also be caused by a leaking seal in the transmission.

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

6 Common Causes of Transmission Fluid Leaks

1. Defective transmission case gasket

Transmission seal leak

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

There are also times when they get old and start to leak as the transmission fluid slowly consumes them.

Some car transmission models use a sealant instead of a gasket, which can also wear out and require replacement.

2. Cracked or rusted transmission case

Removing the transmission case

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

Rust is a problem if you have a steel transmission case. The pans are quite thin in terms of material, and if they start to rust, they will create a hole quite quickly. Check for signs of rust, and if you find any, it’s probably time to replace the pan.

3. Leaking Transmission Pan Drain Plug

Transmission fluid change

Not all automatic transmissions have a drain plug, but some do, and if you have one in your transmission, there is probably a leak. You will usually find an O-ring on the drain plug, which should be replaced after each fluid change.

Most people do not replace this O-ring when changing the fluid, causing a transmission leak after a while.

4. Bent drive plate

Remove the transmission fluid

If someone, before you replaced the transmission fluid, had trouble removing the pan due to, say, a strong sealant, the pan may be bent at the edge.

The steel transmission pans are quite weak, and if someone took a large screwdriver to remove them, there is a risk that they could bend them. Check for damage to the edges of the transmission case. If it is bent, you may need to replace the transmission pan entirely.

5. Transmission fluid line

Transmission line leak

Several automatic transmissions also lack liquid cooling, although not all. If you have a cooled automatic transmission, you most likely have fluid lines going to the transmission cooler at the front of the car.

These lines are steel and tend to rust and start to leak. They also tend to go very close to the pan, so you might think it’s a pan leak, but it’s coming from the transmission line above.

6. Clogged transmission vent

Transmission cover removed

Most automatic transmissions have some type of open transmission vent on the top of the transmission to ensure that it doesn’t create too much pressure inside. These small transmission vents can become clogged on some car models, which will create transmission leaks everywhere.

Look in your transmission for some vent hoses or ask your authorized dealer if your transmission is equipped with a vent. Because they are installed above the transmission, they can be difficult to reach.

Transmission Fluid Leak Repair Cost

The average cost of a transmission fluid leak 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.

These are some examples of repairs that could offset the cost of a fluid leak. Prices include parts, new fluids, and labor. Prices can vary greatly depending on the transmission model, but this gives you a clue.

Type of job Prize
Transmission gasket replacement cost (including fluid and filter) $150 to $400
Transmission Pan Replacement (Including Fluid and 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 the transmission fluid level is good, you won’t damage your transmission with a small leak. However, the best practice is to repair the leak as quickly as possible.

The more you drive a leaky car, the more fluid is drained out. At some point, you won’t have any and your transmission will be damaged. If the leak is small, it can save you time getting to the nearest gas station to get it fixed.

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


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