Water or Coolant Mixed With the Transmission Fluid: Is the Gearbox Ruined?

The mixture of water or coolant with automatic transmission fluid (ATF) can lead to catastrophic failure in automatic transmissions and gearboxes, which is a silent killer for these components. This problem was previously seen in earlier cars with engine cooling systems that were not maintained correctly. Still, it is becoming more prevalent in more contemporary types of automobiles and trucks that have kept to the maintenance schedules provided for them. However, the conclusion is always the same: either a thorough overhaul of the transmission or its replacement is necessary. Neither option is ever an option.

Is It Possible to Eradicate Every Trace of the Contaminated Fluid Before It Can Do Any Harm?

Plates lined with paper derived from cellulose and referred to as clutches or frictions are utilized in virtually every automatic transmission seen on the road in modern times. These clutches provide the role of brakes, making it possible to move and stop various components housed within the gearbox. The frictions are activated whenever the shifter is shifted into the drive or reverse position. Paper is a delicate material that is secured to a steel skeleton, and it is this paper that is used to line the clutch plates in a manual transmission. When I think of the stiffness and feel of the paper before it has adhered to the plate, I can’t help but be reminded of graham crackers. When the material is bonded together, it receives a considerable increase in strength and can endure regular operating conditions for an exceptionally long period.

Transmission Fluid
Image Source: Dub’s Garage

Hygroscopic material is utilized for the construction of the clutch. When the clutches are exposed to moisture, this suggests that the paper material will substitute for ATF instead of water. This happens when the clutches are in the “wet” position. This moisture seeps into the steel plates, which causes rust to develop; also, it destroys the glue that binds the paper to the plate and causes the paper to separate from the plate. According to the findings of a study that International Lubricants Inc. carried out on the subject of the effects of water being exposed to automatic transmission clutches, “The testing indicated that water added at levels as low as 600 mg/kg migrated to the surface of untreated paper frictional and contributed to the loss of the paper coating and erratic torque transfer properties.” This is how the conclusion of the investigation reads. To put this into more understandable terms, there has to be less than a tablespoon of water or engine coolant in the transmission for it to fail.

What brought the water to that location in the first place?

Image Source: Jim Coleman Auto Group

There are three distinct points where water can get into a transmission, and they are as follows:

Through the engine’s cooling system, located in the radiator, most automated gearboxes have been cooled using the same water-based technology that has been in use since the 1950s and continues to be in use now. This technology is responsible for preventing the engine from becoming very hot. The coolant can remove heat from the ATF without the two fluids coming into touch with one another since the transmission fluid is kept in a separate tank within the radiator. When there is a leak in the radiator between the tank for the automatic transmission fluid (ATF) and the tank for the engine coolant, the transmission fluid will mix and get polluted. It happened more frequently in older autos with cooling systems that had deteriorated because of careless maintenance. These cars were more likely to catch fire. Despite this, some of the most recent autos available on the market feature components made of materials that are degrading owing to pressure concerns in the cooling system.

Transmission Fluid
Image Source: The Drive

Exposure to deep water. It is possible to expose the breathing system of the transmission to moisture if you drive off-road or through large puddles while it is raining and if you drive through the puddles. After a vehicle has been exposed to such conditions, the best way to reduce the likelihood of experiencing a breakdown is to inspect the ATF for any indications of water contamination.
The point of entry for any moisture is the dipstick in this system. The dipstick included as standard equipment on most vehicles may be used to check and adjust the amount of ATF. However, if the dipstick is sprayed with water when the engine is being cleaned, or if water pouring from the roof or coming from a carwash drips onto the dipstick, it is simple for moisture to get into the transmission. Other ways that moisture can enter the transmission include: These outcomes are quite conceivable. To solve this issue, General Motors and Chrysler have sent service advisories for specific models of their automobiles affected by it. Establishments that meet the requirements will be granted access to a function that allows them to check for these alerts. An indicator of a problem is the appearance of rust or moisture in the area surrounding the dipstick tube.

Should I Get a New One or Rebuild the Old One?

Transmission Fluid
Image Source: YouTube

It is based on the amount of water mixed in with the transmission fluid, the length of time that the car was driven with the contaminated ATF, and the type of gearbox in your vehicle. When it comes into contact with moisture, the metal and electrical components that are housed inside the transmission will deteriorate at an extremely rapid rate. If there is excessive damage within the gearbox, the price of the parts required to rebuild the trans will be higher than the price of replacing the unit with a remanufactured version of the same product. This is because rebuilding the trans will require more labor. In addition, some manufacturers, like Nissan and Chevy, include computers inside the gearbox, which are prone to malfunction if they come into touch with any moisture. These computers or mechatronics may have a price tag of up to two thousand dollars, which does not include the cost of reassembling the rest of the device. When the cost of the individual parts reaches that degree, it is often more cost-efficient to replace the gearbox in its whole rather than just the sections individually.

Transmission Fluid
Image Source: Guthrie’s Auto Service Inc


There is no way to prevent having to pay for an expensive repair if water gets into the transmission. Regardless of how cautious you are, this will always be the case. The problem will not be solved by flushing out the fluid, and doing so will result in increased expenses and may speed up the vehicle’s eventual failure. Instead, you should do routine maintenance on the engine’s cooling system, and you should enquire with an expert transmission specialist as to whether or not this sort of mechanical failure is usual for the car you own. If this is the case, the radiator should be changed to an external oil cooler.

Mia A Chloe
Author: Mia A Chloe

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