A silent killer for automatic transmissions or gearboxes is the water or coolant that mixes with the automatic transmission fluid (ATF). This problem used to be seen in older vehicles with neglected engine cooling systems, but is becoming common in newer model cars and trucks that have followed their maintenance schedules. The result is always the same: the transmission must be completely overhauled or replaced.
Can contaminated fluid be cleaned before damage occurs?
Virtually all automatic transmissions on the road today use cellulose-based paper-lined plates called clutches or frictions. These clutches act as brakes to move and stop different components within the gearbox. When the gear lever is placed in forward or reverse, it is the frictions that are applied.
The paper that covers the clutch plates is a very delicate material that is glued to a steel column. Before the paper sticks 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 long time under normal operating conditions.
The clutch material is hygroscopic. This means that when the clutches are exposed to moisture, the paper stock will displace the ATF by water. That moisture reaches the steel plates causing rust and breaks down the glue that bonds the paper to the plate. A study conducted by International Lubricants Inc on the effects of water exposed to automatic transmission clutches states: “Test indicated that water added at levels as low as 600 mg/kg migrated to the surface of untreated paper frictions and contributed to loss of paper coating and erratic twist transfer properties.” In layman’s terms, that means less than a tablespoon of water or engine coolant in a transmission can cause a failure.
How did the water get there?
There are three ways that water can enter a transmission:
- Through the engine radiator. From the 1950s to now, most automatic gearboxes are cooled by the same water-based system that prevents the engine from overheating. There is a separate tank in the radiator for transmission fluid that allows the coolant to remove heat from the ATF without mixing the two fluids. When a leak occurs between the ATF and the engine coolant tanks in the radiator, the fluids will mix with each other. It was more common in older vehicles that had eroded cooling systems due to neglect, but some of today’s newer vehicles use materials that fail due to pressure problems in the cooling system.
- Exposure to deep water. Driving through large puddles during rain storms or driving off-road can expose the transmission’s breathing system to moisture. The best chance of preventing a failure is to check for water in the ATF after a vehicle has been in this type of scenario.
- Moisture enters through the rod. Most vehicles have a dipstick where ATF is checked and added. Moisture can easily enter the transmission if the dipstick was sprayed with water during engine cleaning or, in some cases, drainage water from rain or a car wash drips onto the dipstick. GM and Chrysler have bulletins regarding this issue on some models of their vehicles. Authorized businesses will have access to consult for this type of bulletins. A telltale sign of this problem is moisture or rust around the dipstick tube.
Replace or rebuild?
It depends on the amount of water mixed with the transmission fluid, how long the vehicle has been driven with the contaminated ATF, and the type of gearbox your vehicle has. Metal and electronic parts inside the transmission will rapidly corrode when exposed to moisture. If there is too much damage inside the gearbox, 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 gearbox that will fail if exposed to moisture. These computers or mectronics cost up to $2,000 and that does not include rebuilding the rest of the unit. When parts cost this much, it’s often a better decision to replace the gearbox entirely.
Long story short, if water gets into a transmission, there is no way to avoid an expensive repair. Flushing the fluid will only cost you extra money and may cause the inevitable failure to happen sooner. Have your engine cooling system serviced regularly and ask a professional transmission mechanic if your car is common for this type of failure. If so, bypass the radiator with an external oil cooler.