Possible Causes of Big Transmission Fluid Leaks

by Tom Nari
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When you see drip spots on the ground below your car, inspect them closely to determine if you have a leak. Transmission fluid is a bright or dark shade of red, whereas oil is deep olive or black and coolant is green. If you cannot determine the type of leak by the color of the drip spot, then try smelling it instead. Remove the transmission fluid dipstick and smell it. Then wipe up the driveway spot with a paper towel and smell it too. Compare the odors. You can stop some minor transmission fluid leaks yourself with a leak stopping additive, but major leaks will require professional service.

Transmission Pan

Transmission fluid is stored in a pan under the car. Designed to be opened only for maintenance, the pan has a seal that is replaced whenever you service the transmission. Worn or cracked seals will leak under pressure. Generally, a large leak in this area will result in hard shifting or difficulty putting the vehicle in drive. A series of bolts secures the transmission pan to the vehicle. The bolts can loosen over time, causing the pan to leak.

Worn Rear Main Seal

The rear main seal is where the transmission meets the car engine. This area is protected by a gasket which can become cracked, frayed and brittle over time.

Damaged Transmission Fluid Line

Transmission fluid travels through the transmission in a long tube called a transmission fluid line. A hard impact by road debris can damage this line, which is located on the bottom of the car, between the wheels.

Leaky Torque Converter

The torque converter is a hydraulic pump which pressurizes the transmission fluid system and moves the fluid throughout the entire transmission. A leaky or damaged torque converter can cause a serious transmission leak.


Under extreme or prolonged use, transmission fluid can overheat and even burn. High temperatures cause the fluid to oxidize and lose its viscosity. Overheating can occur during stop-and-go traffic, hot weather, street racing or when towing a heavy trailer. An overheated transmission system will emit a strong burning smell and can cause various parts of the system to buckle under pressure, leading to leaks of all kinds.

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