What Causes Transmission Fluid to Increase?

[HannahMarie]

Transmissions have vent holes that allow moisture from the air to enter, which can then degrade the transmission fluid. This is why transmission fluid needs to be replaced periodically. Below is more information about transmission fluid replacement: 1. Introduction: Transmission fluid is used in automotive transmissions to clean and lubricate the gear system, extend the lifespan of the transmission components, and provides functions such as cleaning, lubrication, rust prevention, and heat dissipation. 2. Types: Depending on the type of vehicle transmission, transmission fluid can be categorized into manual transmission fluid and automatic transmission fluid. 3. Replacement Interval: Generally, it should be replaced every 3 years or approximately 100,000 kilometers.

[TimothyRose]

That day I was helping my friend check his car, and it's indeed rare but not unheard of for the transmission fluid to increase. The most likely cause is coolant leaking into the transmission cooler, as these two systems share components which can lead to cross-contamination. It could also be that the vent hole was clogged with mud, preventing gas from escaping and creating pressure that pushed the oil up. Once, I saw an off-road vehicle whose transmission fluid increased after wading through water, and upon opening it up, water had flooded into the transmission, emulsifying with the oil into a milkshake-like substance. Additionally, not bleeding the air from the lines when adding new fluid or inaccurate fluid level measurement could lead to misjudgment. The worst-case scenario is internal component wear producing metal shavings that cause the oil to foam and expand. If you notice the fluid has increased, you should stop driving immediately, as whitish, emulsified oil can directly damage the clutch plates and planetary gear sets.

[VanMila]

It's definitely abnormal for the transmission fluid level to increase instead of decrease. I've handled several similar cases. The common culprit is a punctured transmission cooler, allowing engine coolant to slowly seep into the fluid. Another scenario occurs when driving through water, where water enters through the shift cable seal. Last month, an old Excelle came to our shop with rainwater mixed into the transmission due to seal aging. Additionally, overfilling can happen when adding fluid carelessly, especially when misreading the dipstick on a cold engine. A deformed oil pan or excessive metal shavings attracted by the magnet can also make the fluid appear excessive. Immediate inspection is required when noticing increased fluid, as water contamination can cause bearing rust and seizure.

[SanGarrett]

An increase in transmission fluid volume is most likely due to contamination with other liquids. The most common scenario I've encountered is internal radiator leakage, where coolant and transmission fluid mix. Another instance was when a high-pressure car wash spray damaged the vent cap. Rising fluid levels could also indicate foaming, which occurs when the filter is clogged or the oil pump draws air. I recall a customer who constantly complained about increasing fluid levels; inspection revealed residual cleaning agent from the previous oil change wasn't properly flushed. Milky fluid indicates water contamination, while excessive metal shavings can thicken the fluid, making it appear more voluminous.