Monday, July 22, 2024 Detailed Auto Topics
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The color of automatic transmission fluid can suggest an automatic transmission problem. Using only the color of the fluid as a guide can also be misleading. When transmission problems exist, other symptoms are normally present. We should be cautious of businesses that sell repair based only on the automatic transmission fluid color. Knowing the normal color and looking for other symptoms can help prevent scams.

Many times folks come in thinking they need automatic transmission repair. Sometimes repair is needed and often it is not. The reason these people felt repair was needed is, another shop told them the automatic transmission fluid was dark.  Selling a transmission flush is very profitable and fluid color is often used as an excuse to sell an unneeded service.

The color of new automatic transmission fluid

Clean automatic transmission fluid 

New automatic transmission fluid has a bright to dark red, translucent color. The red color is the result of dye that is added to the transmission fluid for identification. Color is NOT an indication of the quality of the fluid nor the condition. An automatic transmission can have a significant amount of wear and still have clean red fluid.  It could also have dark fluid and still be in great condition.  The color of automatic transmission fluid, taken out of context, means very little.

All transmissions benefit from a proper service, but need is based on mileage and driving conditions.  The color of the fluid alone is not an indication of the need for service.  Many newer fluids are significantly darker than automatic transmission fluid of the past, even when it is new.  Color ranging between the first and second illustration are typical for new fluid.

Dark automatic transmission fluid does NOT necessarily indicate a problem

Automatic transmission fluid also tends to get darker, and more brown in color as it ages. This is normal and does not indicate a problem. The dye used in the fluid changes over time and color change is to be expected.  This illustration shows transmission fluid that was recently replaced, but has a darker color because of the type. 

Heat also causes fluid to darken in color. A more reliable indicator of fluid condition is the time and mileage since the fluid and filter has been replaced. Under normal conditions, automatic transmission fluid will last at least 30,000 miles.  Vehicles used for towing require more frequent service as the transmission tends to run hotter. A proper service every two-years or 30,000 mile is more than adequate, with most transmissions.  Some automatic transmission fluid lasts much longer, unless other problems occur.

Even very dark automatic transmission fluid does not necessarily indicate a problem with the transmission

Dirty automatic transmission fluid 

Even very dark fluid does not show an automatic transmission problem, unless other symptoms are present. Fluid that we have not replaced for 100,000 miles will often be very dark. The automatic transmission may also still be in good condition and only need a proper service.

Even fluid the color that is illustrated to the left, causes few problems.  Restriction of the automatic transmission filter is much more of a problem than dark fluid. This is another reason why automatic transmission flushes are ineffective. Replacing dark fluid and not the filter does not help. With very dark fluid, it may also take more than one service for the color to return to normal.  Many times dark fluid is incorrectly described as burnt. 

Black, burned automatic transmission fluid does indicate another problem 

Burned automatic transmission fluid 

Burnt automatic transmission fluid is almost black in color and has a strong burned smell. If we burn the fluid, simply changing it will do no good. Burnt fluid is a symptom and shows other problems.

The burnt fluid is not the problem, we have burned the fluid because a failure has occurred within the transmission. A few possible causes include slipping clutches, a failing torque converter or bad solenoids. Other symptoms such as slipping and hard shifts will often accompany burnt transmission fluid. With fluid in this condition, only a proper diagnosis and repair can prevent further damage.


Light pink colored fluid shows water contamination

Water or coolant in the automatic transmission

Lighter than normal colored, pinkish fluid is also a major problem. Fluid of this color means water contamination. Water-soluble glue bonds the clutches in an automatic transmission. If water enters an automatic transmission, it will fail. No way exists to flush water from the transmission.

Water enters transmissions in a few ways. Driving on flooded streets or through high water allows it to enter through the transmission vent. Transmission coolers, in the radiator, can also leak. This allows coolant and water to enter the transmission. The only solution is to tear the unit down and replace all affected components. Allowing water to remain in a transmission will cause rust and major failure.

Transmission fluid color should always be considered along with other factors.  A trusted professional can let you know if there is a problem. 


Symptoms that point to a problem

 Slipping, improper shifting, noises or a warning light indicates a problem 

 Time and mileage are a better indicator of a need for service

 Simply flushing dark fluid is NOT a proper service

 All transmissions benefit from a proper service

 Towing with a vehicle requires more frequent service

Also see our article on Properly Checking Automatic Transmission Fluid

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