Dirty Transmission Fluid: Signs And Causes

(Last Updated On: March 14, 2024)

In vehicles, transmission fluid has significant importance. If the transmission fluid becomes dirty, it could hinder the functioning of the entire transmission system. This is why, as a car owner, it’s imperative to realize that the transmission fluid shouldn’t be left unchanged for longer than a specified period.

It, normally, is kept clean by the filter. If the filter is faulty or too old, contaminants are likely to pass through easily, contaminating the transmission fluid. Different transmission fluid colors indicate states of the fluid. Thus, you should be familiar with these colors to know the condition of the transmission fluid you have and its impact.

 How To Tell Transmission Fluid Is Dirty?

ColorMeaningRecommended Actions
Red transparentWhen transmission fluid is purchased, it is usually red-transparent in color.
Ideally, this is the original color of pure transmission fluid.

You should try as much to keep the fluid in this color. Clean transmission fluid promotes the smooth operation of the gear.
Light brown semi-transparentIt indicates a good state of the transmission fluid.It is vital to regular checkups to detect problems. The issues may include leaks and contamination.
Dark brown opaqueIf your transmission fluid has this color, it may be old or stale because of the oxidization of the transmission fluid. Thereby, the transmission fluid does not lubricate enough as needed.Therefore, you will need to change the transmission fluid immediately to avoid future complications. It is also crucial to check the filter while servicing the car.
Very dark brown or blackThis color shows that your transmission fluid is very dirty or contaminated. The fluid in your transmission may cause overheating and future leaking.All you have to do is a fluid flush to change it completely. Also, installing a new filter is recommended since the fluid gets contaminated if the filter is faulty or old.
Light pinkWhen water/ coolant has mixed with the fluid, it becomes light in color. Hence, when the transmission fluid is in this color, it may lead to the failure of the transmission.
The transmission fluid can get contaminated by dust, oxidization, or water.

Hence, the car needs to be taken for service. During servicing, the transmission oil cooler line-radiator should get checked. This is because the water has a high probability of passing through here to reach the fluid.

Read more: Bad Torque Converter Vs. Bad Transmission

What Makes Transmission Fluid Dirty?

Faulty transmission fluid filter

The main function of the filter is to prevent contaminants such as metal filings, debris, and dust from getting through to the fluid. Leaking and complications when changing gears are signs of a faulty transmission filter. Therefore, you should change the transmission filter every 30,000 miles or approximately two years.

Damaged breathers in the gearbox 

Moreover, the gearbox has an opening that allows contaminants to go through quickly. On the other hand, the breathers prevent contamination of the transmission fluid. Therefore, if they are faulty or too old, contamination will happen. In addition, contaminants may get in the transmission fluid during packing.

Old or stale transmission fluid

Another mistake that some people do is unknowingly adding new transmission fluid to the old one left. The old one might be dirty and when you mix it with the new fluid, it will affect your system. Hence, one should do a fluid flush to remove all the old fluid. Also, while maintaining the machine, you might accidentally pour some water into the transmission fluid, which is also a reason for contamination.

Dust is a contaminant that gets in very quickly. If you are fond of driving in very dusty areas, always change your filter regularly.

Read more: Transmission leak: Symptoms, causes and repair guide

Effects Of Dirty Transmission Fluid 

Dirty transmission fluid effects
Dirty transmission fluid can cause serious problems to your car.

Warning light

This indicates that the transmission is overheating since the fluid is running low.

Transmission overheating

Frequent overheating of the transmission may cause leaking of the transmission fluid. A common sign of an overheating transmission is slipping of the gears while accelerating or decelerating. Gear slipping may occur due to a lack of adequate hydraulic power.

Difficulty in shifting gears

Contaminated transmission fluid is most likely to cause delayed gear shifting. Inadequate lubrication makes the gear shift hard.

Transmission fluid leakage

Overheating and debris contaminants in the transmission are the main causes of transmission fluid leaking.

Generation of unusual sounds

There is the production of unusual sounds when the transmission fluid level is low or when the fluid is contaminated.

Transmission slipping problems

 Insufficient lubrication also causes gear slipping. The driver can tell the transmission is slipping when changing the gears. There may either be a delay or hardness to shift gears.

Read more: Transmission flush: Never do it before reading this guide

How To Change Transmission Fluid

Any car owner needs to have the transmission fluid changed. The stale fluid may destroy the transmission and other contaminants present easily. In addition, if you do not change the transmission fluid, you may be promoting future complications with your system. The transmission fluid changes should be done after every 30,000 to 100,000 miles covered by the car.

Some of the equipment required before changing the transmission fluid is:

  • A catch pan where the old transmission fluid is transferred from the fluid pan to it.
  • Transmission pan gasket
  • New transmission fluid filter
  • A hydraulic car jack

It is advisable to flush all the old transmission fluid to avoid contamination of the new fluid and complications in the transmission due to impurities.

  • Ideally, before flushing the old transmission fluid, you will preheat the facility.
  • Removal of the entire pan is done to drain all the transmission fluid. Remember to replace the filter with a new one when changing the fluid. However, the quantity of canister oil is usual seven liters to about eight liters.
  • After draining out all the old transmission fluid, you are to insert the new transmission gasket.
  • After re-installing the transmission fluid pan, pour in the appropriate amount of the fluid.
  • The next step is to run the transmission while shifting gears without moving the car. The fluid is being circulated.
  • Finally, the dipstick is returned to the transmission dipstick sleeve. What’s next? Don’t you close the cap or something like that?   
Let’s find out how to change your transmission fluid properly!


1. Can dirty transmission fluid cause transmission problems?

Yes, dirty or contaminated transmission fluid has negative effects on the transmission. Dirty transmission fluid can cause overheating, leaking and gear slipping. 

2. What happens if we keep using dirty transmission fluid?

It may cause further damage to your transmission such as loss of hydraulic power that causes gear slipping. Gear slipping is a result of a lack of enough lubrication. The transmission fluid flow will be affected, while the operation will not be smooth.

3. Is it better to flush or drain dirty transmission fluid?

A fluid flush is better than a fluid drain since it involves removing the fluid from the pan, the cooler lines, and the torque converter. This means that a new fluid will run in the system. There are very minimal chances to have contaminants after a fluid flush.

4. Should I change my transmission fluid if it’s brown?

Yes, you should change the transmission fluid if it is dark brown opaque. The color indicates that the transmission fluid is too old to be used. If you continue using this stale fluid, you will not get the lubrication required for gear shifting.

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