When asked what the number one problem with automatic transmission fluid is, it has never changed or gone away as technology improves and changes. I would have to say the answer is water. It’s the problem that never goes away, and hardly a month goes by that I do not have at least one, but usually multiple calls concerning the problem of water or coolant contamination.
Water can be an insidious problem for anything automotive with an engine or transmission. Not only can it have harmful permanent effects on internal components and hard parts, but it can also have a very direct function in the premature aging and contamination of the oils used to lubricate the drivetrain. Contamination by water or ethylene glycol coolant in most lubricants (synthetic or mineral base stocks) can dramatically increase oxidation, causing premature aging of the oil.
Certain types of synthetic base oils, like phosphate esters and dibasic esters, are known to react with water, degrading and destroying the base stock and encouraging the formation of acids that corrode electronics and wiring.
It’s not just the base oil that can be damaged by moisture or coolant contamination. Other additives, such as demulsifying agents, dispersants, detergents, and rust inhibitors, can be washed away by excessive moisture, leading to rust accumulation, sludge and sediment buildup, plugged filters, and the formation of oil/water emulsions (white or pink paste). Not only will water or coolant overwhelm the ability of the additive package to protect from rust and corrosion, but it will also directly attack the frictional component of the additive package and interfere with friction performance, causing problems like shudder during engagement or gear changes, especially during torque converter engagement or lockup.
Water can enter a transmission in several different ways, from direct ingress of fresh water from driving in deep water, vehicles sitting in flood water, or contaminated ATF that was stored or handled improperly. Coolant contamination from ethylene glycol and water can enter from leaky radiator-mounted heat exchangers. Atmospheric condensation or absorption (especially common in marine zones near large bodies of water) is probably the most common source mode of water entry in most situations, especially where the new, reduced-viscosity “synthetic” OEM-specific ATFs are concerned.
Transmission fluids, like most lubricating oils, are, by nature, somewhat hygroscopic, with certain synthetic base oils much more prone to this than others. These oils can absorb water at levels from 100 ppm (0.0001% water by volume) to 2000 ppm (0.002% water by volume) directly from the air. The amount of water absorbed not only depends on the environment (temperature, pressure, humidity) but also on the type of additive package (the greater the additive content, the higher the water absorption capacity), making some synthetic HFM (highly friction-modified) type ATFs more prone to water contamination.
Water can also compromise the friction modifier system of automatic transmission fluid by competing with it for the friction surfaces of the clutch packs and the torque converter. It’s true that a certain amount of water can be present in the bulk fluid, causing corrosion and electrical component degradation without having a major impact on friction characteristics in the clutch interface until a threshold concentration is reached. Once this occurs, the water will actively compete with the friction modifiers for the fiber frictional material plates and the metal separator plate surfaces. Once the water or coolant concentration is sufficient to damage frictional performance, it is probably already attacking other transmission components and components of the additive package. Water will eventually disrupt and destroy the bonding of the fiber friction linings on steel-backed clutch plates. This is because the high temperatures generated at the plate interfaces turn water to steam, causing the bonding resin to delaminate the frictional material from the steel backing plate. This quickly contaminates the entire transmission with debris and wear materials. Glycol contamination will also physically deteriorate clutch plate materials and has the potential to damage electrical components and solenoids.
There are basically two forms of water found in transmission fluid. The first is “dissolved” water, where the water is bound by the polar molecules of the lubricant additives (for example, the dispersant system that holds contamination in suspension in the oil). When this occurs, the oil appears clear, making contamination difficult to detect. The second form of water is “dispersed” or “free” under conditions where the transmission fluid is essentially supersaturated. When this occurs, the dispersed water can be in the form of a pasty emulsion that is white, red, or pink in color for red ATF (amber, blue, or greenish white emulsion for other ATFs) or appears as cloudy patches in the oil with free water usually settling to the bottom of the oil pan or sump. Dissolved water is often first detected by the onset of frictional problems, such as low-speed frictional issues like torque converter shudder.
Very often, changing the fluid solves the problem, and it was the initial fluid problem identified by GM when the “new” 8-speed transmissions first came out in 2018. In December of 2018, GM Global Select issued a dealer alert for the Southeast and South- Central regions of the US. Frequent complaints from T/C shudder caused GM to replace the Mobil1 HP fluid it was using for the new transmission due to concerns related to our old nemesis, water. The message was clear: “The current HP fluid has a greater tendency to be hygroscopic – or water absorbing. It also tends to hold that moisture even when the fluid heats up. As the moisture content in the fluid increases, the tendency to have T/C shudder increases”. The Global Connect message included a copy of the service procedure and the required tool kit, with a March 2019 delivery date as the target for the new fluid. The new fluid was also Mobil 1 HP LV with a black label, and it remained in service until 2020, when another service bulletin called for the replacement of that oil with the new (purpose-blended for GM by Mobil for this transmission and the T/C shudder problem) Mobil 1 HP LV with the blue label. This has remained the service fluid specified by GM and is available at all GM dealerships and parts outlets. This “fresh fluid” solution does not apply when the second form of “dispersed” or “free” water occurs, and any amount of water or glycol in concentrations greater than 200,000 ppm (0.2% water by volume) requires complete disassembly and cleanup of the transmission. On top of that, the GM service bulletins tell you the transmission should be rebuilt, and the following components must be replaced:
- Replace all rubber-type seals.
- Replace all the composition-faced clutch plates and/or bands.
- Replace all nylon parts.
- Replace the torque converter.
- Completely clean and rebuild the transmission using new gaskets and an oil filter.
- Flush and flow check the transmission oil cooler.
- Inspect, clean, and repair the engine cooling system and hoses as needed.
The message is that free and dispersed water, creating a supersaturated transmission fluid, poses the most immediate and destructive condition your transmission can encounter, whether in normal or severe service. Not only does it destroy the additive system and frictional package, but it also severely reduces the fatigue life of bearing surfaces by displacing the fluid that protects the contact zone and, through a complex set of chemical reactions, embrittles the metal surfaces and destroys the hard parts and bushings.
If the water contamination is minimal, the amount of water or glycol may be due to an unsuspected source of the contamination. Improperly stored, uncovered, upright drums of ATF can be a problem, with rain and rapid ambient temperature changes, causing water to literally be sucked into the drum of transmission fluid. In some situations, water flows over an open transmission vent tube or dip stick/fill tube.
In the case of ethylene glycol, the accidental use of an all-purpose fill container can become the source of contamination when it’s used for ATF. Regardless of how it gets there, water and coolant contamination are ever-present potential problems for the transmission owner, service technician, or shop owner, and must be factored into the diagnostic process when trying to solve frictional or shift quality issues.
Water content is detected and measured using several methods, from simple bench tests to sending out samples to a test lab. The oldest and easiest is the water crackle test. It’s a simple and quick procedure to estimate water content above 500 ppm. A few drops of the ATF to be tested are placed on a hotplate that is 135 deg. C. The water in the oil will start to bubble, with the bubbles generated by evaporating water giving you a rough idea of the water content. If a more precise measure of water is desired, the Karl Fischer Water Titration test will provide the answer, but the fluid sample must be submitted to a test lab.
Once water in the ATF has been found and the source of the water has not been determined (or if a leaking in-radiator transmission fluid cooler may be bad), a simple, quick test is available that detects the presence of ethylene glycol in ATF. These test strip kits are available at most automotive aftermarket outlets and allow a quick determination of where to start looking when the presence of water is suspected or detected.
It’s a problem that never goes away, and the source of water contamination makes proper diagnosis frustrating and elusive. Doesn’t matter if it’s new fluid or used fluid with lots of miles on it; water contamination can suddenly appear with problems that range from annoying frictional problems to catastrophic failure, depending on how quickly you figure it out.
If you have concluded that the fluid is contaminated with water or glycol and the transmission seems to be working fine, you may be able to “save” the transmission with a simple transmission fluid exchange. Unfortunately, there is no guarantee this will fix any damage that has already occurred. The transmission may run fine for 50,000 miles or fail in a few days or weeks; again, it depends on how bad it was and how quickly you figured it out. When it’s a customer’s vehicle, you need to warn them about the potential for problems or actual transmission failure due to contaminated fluid, and make sure they understand the situation and its consequences. It’s always the last thing you want to hear, but it may be one of the first things to look at when fluid-related problems occur.
