About Your Transmission

Changing automatic transmission fluid is best left to a mechanic equipped with a transmission flusher which replaces the fluid more thoroughly than you could achieve with gravity alone.

Transmission fluid is a slippery liquid that acts as a lubricant for all of the moving parts inside your transmission. In an automatic transmission, this fluid also serves as a coolant and a viscous fluid that transmits power from the engine to the transmission.

A variety of fluids are used for different transmissions. Automatic transmissions use something called — shockingly — automatic transmission fluid. Manual transmissions use a variety of oils: regular motor oil, heavyweight hypoid gear oil or even automatic transmission fluid in some cases. Your owner's manual will tell you what your transmission calls for.

Should I do this service when it's recommended?

Yes, definitely, regardless of whether you have a manual or an automatic transmission.

Manual: Most manufacturers recommend that manual transmission fluid be changed every 30,000 to 60,000 miles. Under heavy-duty use, some manufacturers suggest changing transmission fluid every 15,000 miles.

Automatic: Service intervals for an automatic transmission vary from every 30,000 miles ... to never. The typical service interval is 60,000 to 100,000 miles. Changing it more often does no harm.

Why do I have to do this?

Manual: In a manual transmission, the problem is not so much the fluid degradation, but rather fluid contamination. This contamination occurs over time as the synchronizers, bearings and gears in the transmission wear out. The resulting metal particles then float around in the lubricant. And we all know that oil with microscopic particles of metal in it does not lubricate as well as clean oil. So if these contaminants are not drained out, they will shorten the life of your transmission.

Automatic: Because more heat is generated in an automatic transmission, automatic transmission fluid actually degrades and breaks down with use.

In addition, like in a manual transmission, automatic transmission fluid will also become contaminated with worn bits of the transmission. If these contaminants are not drained out, they will shorten the life of your transmission.

What happens if I don't do this?

If you don't change the transmission fluid on schedule, you'll be lubricating your transmission with metal shavings and other contaminants. This will shorten the transmission's life. The result could be a hefty boat payment to your mechanic. In other words, changing your transmission fluid at the correct interval is a good investment.