Why Is My Transmission Fluid Brown? (9 Reasons Why)

Your car’s transmission is a sophisticated device that transfers power from the engine to the wheels. If you notice that your transmission fluid is brownish or smells burnt, there are several reasons why this could happen.

Transmission fluid is a particular type of petroleum-based product that has been designed to lubricate the internal moving parts in your engine. Here’s what we will reveal as to why your transmission fluid is glazing brown!

Why Is My Transmission Fluid Brown?

Your transmission fluid is brown because it’s old, dirty, contaminated, and oxidized. In addition, your transmission fluid may have been sitting in your car for years, maybe even longer than you’ve owned it. Because of that, it can make the fluid produce a shiny juice brown color, which is a sign it’s time to change it out.

Let’s dig deeper to discover why transmission oil turns brownish over time, so tune in!

1. Fluid Is Old And Dirty

If you have driven many miles and been driving in areas with high air pollution, your transmission fluid will begin to turn brown.

Because of that, the older the fluid gets, the more it will deteriorate and become polluted with dirt and other particles that can clog up your transmission lines.

As well as that, transmission fluid contains lubricants and anti-wear additives, which means that it’s designed to help keep gears moving smoothly.

As a result, if some filth and spoilation are present in the system, it will show up as an ugly brown color.

2. Contaminated And Oxidized

Contamination can be caused by oil, grease, and coolant leaking into the transmission system.

Along with that, it might be caused by metal particles in the air or on your car’s exterior that have found their way into your transmission system through cracks or crevices.

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However, if you notice black marks on your transmission pan, this is another sign that something has gone wrong with your car’s maintenance schedule.

Overall, as it is exposed to road grime, rainwater, dust, and grit from road surfaces, transmission fluid will eventually turn into a brownish scheme.

3. Electrochemical Degradation

Electrochemical degradation is a chemical process that occurs when an electrical current passes through a solution or electrolyte.

Eventually, the fluid becomes even more acidic and less dense when it gets hot. As a result, it can cause sludge build-up in the system and clog filters and lines.

In addition, when the fluid gets hot, the pH level changes slightly, making it harder for additives to work effectively so that they don’t provide any protection against corrosion or wear on parts.

Inevitably, when the transmission fluid is exposed to the air at high temperatures, it will decompose into its constituent chemicals and turn brown.

4. Metal Shavings

Metal shavings in the transmission fluid may result from regular wear and tear or indicate more severe problems.

In addition, a metallic powder that develops from normal transmission wear may be all over the pan, especially around the built-in magnet.

However, don’t get alarmed if this powder is the only indication of metal shavings. Everything about it is normal, and your transmission will still function perfectly.

By all means, although metal shavings are considered harmless for cars, it still leads to a brown pigment on the fabric inside your car’s engine.

5. Sludge And Sediments Build Up

Sludge And Sediments Build Up

Sludge is a mixture of organic matter that accumulates in your transmission fluid, while sediment is any solid material that floats to the top of your transmission fluid.

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As you can imagine, these two things build up over time, which can cause your transmission fluid to turn brown.

Consequently, this clog occurs when dirt, metal shavings, or other debris gets stuck in the filter and cannot be removed.

By that very fact, transmission fluid is brown because it contains thick sludge and sediments.

6. Excessive Oil

Transmission fluid comprises several ingredients, including anti-wear compounds, friction modifiers, and rust inhibitors. But one element, in particular, stands out: oil.

That said, if you overfill it, the transmission will slip and have a difficult time shifting.

Also, overfilling your gearbox will result in the fluid losing its ability to lubricate, which is another negative effect. Additionally, it can cause the system to malfunction and blow up completely.

For that reason, if massive oil has been put on your car’s engine, it may accumulate, thicken, and turn into a brown shade.

7. Transmission Fluid Should Be Replaced

Brown transmission fluid is a sign that your transmission needs to be replaced. Thus, the transmission fluid in your car needs to be replaced every 30,000 miles or six months.

Additionally, transmission fluid degrades after prolonged use. Therefore, you might want to significantly speed up your timetable if your car is frequently driven at high speeds.

As an outcome, you’ll get brown transmission fluid in your car’s oil pan and down into your engine, and is a sign to replace your juice at once.

8. The Transmission Fluid’s Overheated

When the transmission fluid cools, it turns from a clear to yellowish-brown color. The reason why it’s brown is that it absorbs ultraviolet energy from sunlight.

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In other words, this heat causes the transmission fluid to absorb more ultraviolet energy than it can handle.

As well as that, if you do not replace your transmission fluid right away, your vehicle will continue to broil until you have time to get a new transmission fluid installed in the car.

That being the case, overheated fluid can severely damage your car’s engine, leaving a brown spot on your drivetrain.

9. Water In The Transmission

Water can enter a transmission through cracks in the lines or if it’s not filtered correctly. On top of that, the air conditioning system can also push it in, turning brown if it evaporates.

Furthermore, rust can form from exposure to air and road salt, so if your transmission fluid is brown, it is probably the source.

Further, if you see water in your transmission fluid, first check if it’s from an external leak that’s either dripping or splashing onto the casing of your vehicle.

Overall, the color of your transmission fluid is usually brown because water is not adequately filtered inside the vehicle system.

To know more, you can also read our posts on why your Bluetooth is not working in your car, why your car is cranking but not starting, and why your car is losing power.


For many years, the only thing known about transmission fluid was its purpose—to lubricate moving parts and prevent them from getting stuck.

Now, we know that brown transmission fluid is a sign that the fluid is old, filthy, contaminated, and oxidized.

Remember that your car’s transmission is a complex machine responsible for conveying power from the engine to the wheels, so you must maintain it properly!

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