In general, mechanics recommend regular replacement of transmission fluids for ultimate transmission performance. According to Trust My Mechanic.com, the transmission fluid should be changed every 25,000 miles. However, there are risks associated with changing transmission fluid. Most of the problems occur with older, poorly maintained vehicles, but newer cars can also encounter some of the risks as well.

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Slipping

• One of the main risks involved with changing the transmission fluid in a car is only a concern for high-mileage vehicles that have not had regular transmission fluid replacement. Vehicles with over 80,000 on the same transmission fluid build up a grime of grit and metal shavings inside the fluid. Over time, this gritty fluid actually helps the performance of the transmission because the transmission gets worn away by the particles in the liquid. When the liquid is changed, the new liquid can cause the transmission to slip because it has nothing to grab onto any more.

Fluid Particles

• Another risk associated with changing the old standard transmission fluid is the risk of some of the old fluid remaining in the transmission system. These fluid particles will mix with the new fluid, which can rapidly contaminate the new fluid. Once the fluid is contaminated, you are back to where you started. Unless you flush the old fluid out entirely, there are few benefits to switching out the transmission fluid.

Dirty Filters

• Not changing the transmission filter along with the fluid can also cause a similar contamination risk as not removing all particles of original fluid from the transmission system. The filter should always be replaced when the fluid is replaced to avoid the risk of contamination.

Flushing Risks

• One common way that mechanics change the transmission system fluid is to flush it out with a pump system and replace it with new fluid. If the pressure of the pump is too high, the entire transmission system can become damaged. The high-powered flushing can also knock debris and grit that are inside the transmission system loose, which will contaminate the transmission system and may require extensive repairs.

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