Water or coolant mixed with the transmission fluid: Is the transmission ruined?

Water or coolant mixed with the transmission fluid: Is the transmission ruined?

The silent killer of automatic transmissions or gearboxes is mixing water or coolant with automatic transmission fluid (ATF). This problem used to occur in older vehicles with neglected engine cooling systems, but is becoming common in later model cars and trucks that have followed their maintenance schedules. The result is always the same: the transmission must be completely repaired or replaced.

Can the contaminated fluid be cleaned before damage occurs?

Almost every automatic transmission on the road today uses plates lined with cellulose paper called clutches or clutches. These clutches act as brakes to move and stop various components inside the gearbox. When the gear lever is placed in drive or reverse, friction is applied.

The paper that lines the clutch plates is a very delicate material that is glued to a steel backbone. Before the paper is glued to the plate, it has the strength and consistency of a graham cracker. Once the material is bonded, it becomes much stronger and can last a very long time under normal operating conditions.

The connector material is hygroscopic. This means that when the clutches are exposed to moisture, the paper material will displace the ATF for water. This moisture reaches the steel plates, causing rust and breaking down the glue that binds the paper to the plate. A study done by International Lubricants Inc on the effects of water exposed to automatic transmission clutches states: ‚ÄúTesting has shown that water added at levels as low as 600 mg/kg migrates to the surface of untreated paper frictions and contributes to the loss of paper. coating and erratic torque transfer properties.” In layman’s terms, this means that as little as a tablespoon of water or engine coolant in a transmission can cause damage.

How did the water get there?

There are three ways water can enter a transmission:

  1. Through the engine radiator. From the 1950s to today, most automatic transmissions are cooled with the same water-based system that protects the engine from overheating. There is a separate transmission fluid reservoir in the radiator that allows the coolant to take heat away from the ATF without mixing the two fluids. When a leak occurs between the ATF and the engine coolant reservoirs in the radiator, the fluids will mix with each other. This was more common in older vehicles that had eroded cooling systems due to negligence, but some of today’s newer vehicles use materials that fail due to pressure problems in the cooling system.
  2. Deep water exposure. Driving through large puddles during a rainstorm or off-road driving can expose the transmission breathing system to moisture. The best chance of preventing failure is yes check for water in ATF after the vehicle has been in this type of scenario.
  3. Moisture entering through the dipstick. Most vehicles have a dipstick where the ATF is checked and added. Moisture can easily enter the transmission if the rod has been sprayed with water while cleaning the engine, or in some cases water from rain or a car wash drips onto the rod. GM and Chrysler have bulletins addressing this problem for some of their vehicle models. Qualified stores will have inspection access for these types of bulletins. A clear sign of this problem is moisture or rust around the dipstick tube.

Exchange or refund?

It depends on how much water has mixed with the transmission fluid, how long the vehicle has been driven with the contaminated ATF, and the type of transmission on your vehicle. The metal and electronic parts inside the transmission will corrode quickly when exposed to moisture. If there is too much damage inside the transmission, the cost of parts to rebuild the transmission will exceed the cost of replacing the unit with a remanufactured product. Some manufacturers like Nissan and Chevy have computers inside the transmission that will fail when exposed to moisture. These computers or mechtronics cost up to $2000 and that doesn’t include rebuilding the rest of the device. When parts cost so much, it’s often a better decision to replace the entire transmission.

To sum things up, if water gets into a transmission, there is no way around an expensive repair. Flushing the fluid will only cost you extra money and may cause the inevitable failure to happen sooner. Service the engine cooling system regularly and ask a professional transmission mechanic if your vehicle is prone to this type of failure. If so, bypass the radiator with an external oil cooler.

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