Transmission Fluid

Part 2 of the Essential Fluids Series

It is a slick red (or blue) liquid with a very distinct feel and odor. But what does it do and why is it important.  In this post, we will review transmission fluid and whether or not you really need to change it or even think about it.

Photo by Gary Pradel

The Purpose of Transmission Fluid

In a typical transmission, whether automatic or manual, there are large gears that mesh together at tremendous speeds. This action is what causes your car to move. But the massive amount of friction also creates tremendous heat. The purpose of transmission oil is to reduce the amount of friction between certain parts and also reduce the heat generated by the transmission. Transmission fluid has to have some pretty amazing properties. It has to be slick, withstand high temperatures, be able to flow in cold temperatures, not foam up, not boil off (much), clean and protect metal (the gears), it must contain dispersants, detergents, inhibit rust, and much more.  That is a lot to ask from any fluid.

Because of the variety of transmissions in the market, there are many different types of transmission fluid. The most basic difference is fluid for manual versus automatic transmissions.  But there are also many types of specialty transmission fluids such as Mazda FZ fluid for the SKYACTIV-Drive (which, by the way, is blue in color).

Signs of Wear

With all of the pounding automatic transmission fluid takes, it seems likely that it would eventually break down or fail.  It can. In fact, there are some signs to look for to help prevent problems. The more proactive you are, the better. If you feel like your vehicle is slipping, stalling for no reason, or making a screeching noise, it may be too late.  Often the damage is done before these warning signs. So, again, it is best to be proactive.

Checking the Fluid

You will hear me say it a lot, but be sure to check your vehicle owner’s manual.  It will give you specific instructions for telling you how to check your transmission fluid level. And, it may even tell you that you can’t. That is correct, some transmissions are sealed, like the one on my Pontiac G6. You cannot check the level. However, you can check the fluid level on most vehicles.

Besides making sure the level is correct, make sure to take a good look at the color of the fluid.  I like to use a nice, clean white paper towel and wipe the fluid on it. I’m not good at judging color, so I will also put a little fresh, clean transmission fluid from a new bottle on the same paper towel.  If the used transmission fluid is a much darker brown than the new fluid, you likely have an issue.  If the vehicle is having problems, you may need to take the car in for servicing.

If the fluid was low and you topped it off, it is also a good idea to place a clean white poster board or other similar board under the car overnight. Check to see if any red or brown fluid has leaked onto the board overnight or over the course of a few days.

Do you Need to Change Your Transmission Fluid?

Yes. It is very important to change your transmission fluid. Some recommend every 50,000 miles, some manufacturers say every 100,000 miles. Again, check your vehicle owner’s manual. But I recommend at least every 50,000 miles. You can change it even more often if you like.

Written by Gary Pradel