5 Causes of Water in Transmission Fluid and Solution

Difficulty changing your vehicle gear or hearing a screeching sound when you do so could mean that your transmission fluid is contaminated.

Many things could cause contamination, including water or coolant in transmission fluid. Transmission housing crack, damaged seal, damaged radiator or vehicle emerged in flooded area are the common causes of water in transmission fluid. This issue is highly destructive, causing rust, resulting in friction and difficulty shifting gear.

Once you notice that your transmission fluid has been contaminated, you must take immediate action else you will experience water in transmission symptoms. 

transmission fluid mixed with water

What Causes Water In Transmission Fluid?

There are many causes of transmission fluid mixed with water. A damaged transmission seal or faulty transmission cooler can cause the antifreeze to mix with the transmission fluid. To determine the cause of water mixed with transmission fluid, you must first determine if it is water in the fluid. You can do this by physically inspecting the contaminated transmission fluid.

Below are the causes of water in the transmission or transmission fluid mixed with coolant. 

1. Cracks

Cracks in any part of the fluid transmission housing could cause water or other contaminants into the fluid. As we know, water has a large amount of flow and can get into major parts of the car when it is raining or washing the vehicle. Water can find its way into the wrong places as long as there is an opening. Once there is a crack or leak in the housing, water will enter.

2. Damaged gasket

The transmission gets hot when driving; just like the engine does, this is when the coolants come to play. Coolants are passed over the transmission cooler by the radiator when the engine needs cooling, allowing the fluid to cool the transmission system. These two compartments are divided by gaskets. As time passes, the gasket becomes thinner until completely worn out, and coolants escape into the transmission system.

3. Faulty radiator

The radiator is responsible for supplying the engine and other parts of the vehicle that need cooling with coolants. Due to bad coolants or long time usage, the radiator can often get damaged and allow coolants to settle at the bottom where the automatic transmission intercooler is. As time goes on, oxidation happens from the inside and outside. The coolants or any other liquid escape into the transmission system. Thus, test radiator function before driving your vehicle.

4. Deep Immersion in water

Another reason water could get into the transmission system could be due to driving in flooded areas, large puddles, or more. When water is forced into the vehicle and engine system, it escapes into important places, including the transmission system.

5. Water through the dipstick

You must be careful with water, especially when close to the dipstick. If you clean your vehicle close or directly on the dipstick tube, it could get to the transmission fluid.

Can Water Get Into A Sealed Transmission?

An automatic gearbox has better sealing that does not allow water inside transmission. On the other hand, the manual gearbox has its sealing but also has drain holes, allowing water into the transmission system.

In an automatic transmission, water can only get into the system if the seal is damaged or there is a leak or opening in other parts of the method where water can come in. 

What Happens When Water Enters Gearbox?

If water finds its way into your gearbox, it has some symptoms that make driving difficult, especially when shifting gears. Some of these symptoms may include the following.

1. Difficulty in shifting gear

One of the most obvious symptoms of water in the gearbox is difficulty changing gears. When you begin to notice this, it means that water has been able to contaminate the friction plates. Once the friction plate is contaminated rust builds up, causing limited or no movement. It is when you find it difficult to shift gear, or the gear does not shift at all. Even a small amount of water in the gearbox could damage the friction plates.

2. Noise with shifting gear

The gearbox is not designed to make noise when you shift gears. When you hear screeching when changing the gear, your gearbox has been contaminated with water. This water has then caused increased friction in the system’s moving parts, resulting in the sound you hear.

3. Damaged clutch plates

Once water enters the automatic transmission system, it attacks the clutch’s friction lining. It will damage or destroy the adhesive that binds the clutch plates. Once the water contacts the adhesive, it creates sticky lumps and a way for leak-outs.

4. Increased rust

Generally, when water makes contact with iron parts that have not been properly coated, it creates rust. It is the same with the transmission system. Many iron parts in the transmission system could be corroded when in contact with water. The more the build-up of rust, the more the transmission system fails.

How Do You Get Water Out Of Transmission Fluid?

If you notice water in auto transmission, avoid driving your car and get flushed quickly. There is no possible way to separate the water from the transmission fluid, especially in the vehicle. In this case, you need to have the transmission fluid drained immediately.

Below is an easy-to-follow step to drain your vehicle of contaminated or bad transmission fluid.

1. Park your vehicle in a leveled area and shift the gear to park.

2. Put on your gear like gloves and glasses.

3. Jack your vehicle to grant you better access to the transmission pan. Remove the transmission pan with a wrench.

4. Find the drain plug and screw it. Ensure that there is a drain pan or a bucket beneath the drain plug before removing the plug.

5. Drain the transmission fluid till it is empty, and screw the drain plug back into place.

6. Refill the transmission fluid in the reservoir.

7. Find the cooler-out line and disconnect it from the cooler. Place one tube end over the ling and the other in a bucket or drain pan.

8. Ask someone or your assistant to start the engine and place it in neutral.

9. One person has to watch the fluid draining into the bucket while the other continues to pour the transmission fluid into the reservoir.

10. Do this until the fluid draining into the bucket is clean.

11. Turn off the engine and connect the line back to place once done.

Removing water from transmission fluid is quite easy if you follow the steps properly without skipping any.


Regularly checking your transmission fluid for contaminants like water or coolants can help you prolong the lifespan of your vehicle’s transmission system. Do this by checking the transmission reservoir.

Also, pay attention to the gearbox’s condition and how it works. Observing the gearbox for symptoms when shifting gears, you can notice signs of a contaminated transmission system.

Akindayini Temiloluwa

I am Akindayini Temiloluwa, an automotive expert writer and car enthusiast. I have over three years of experience in the automotive writing niche and have completed over 300 pieces of content from 50 projects. I have vast knowledge and skill in vehicle repairing, all mechanical work, car upgrades and maintenance. My goal as an automotive content writer is to simplify the most challenging concepts for my readers, help them self-diagnose what may be wrong with their vehicles and offer real value for their time.

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