Like oil, different fluids can also get dirty

After my last column on transmission fluid, one of our readers thought it would be good if I wrote about some of the other fluids that need to be changed on a car.

So today I will focus on driveline fluids. They would include the automatic transmission, the differentials and transfer case fluids if the vehicle is four-wheel or all-wheel drive.

We touched on the automatic transmission fluid last time, but let's go a little more in depth today. I believe a 30,000-mile interval is a good rule of thumb.

There are a couple ways that you can change the transmission fluid. You can remove the transmission oil pan, drain the fluid and change the filter, or on some cars there is no filter — you simply remove the drain plug and perform a drain and fill.

The other way, which is preferred, is to hook up a machine and do a transmission fluid exchange. This is preferred because with this method you can change 98 percent of the old fluid while the other method ends up leaving two or three quarts of dirty fluid in the transmission.

Sooner or later, though, you will need to drop the pan and change the filter. Always be sure to use the correct transmission fluid for your car; there are many different types and using the wrong one could cause shifting problems and possibly damage the transmission.

The differential should have its fluid changed at the 30,000-mile interval, as well. Typically all you do with a differential is drain it and refill it with the proper fluid. Once again be sure you are using the correct gear oil for your vehicle.

If you have a four-wheel-drive vehicle, there will most likely be a front and rear differential with a transfer case in between. Be sure to change the fluid, and put the proper fluid back in all of these.

Many of the Jeep products call for these fluids to be changed every 15,000 miles. You should also change them more often if you do any off-road driving because you could get moisture in the differentials which, if left in there, could damage them.

The major cause of transmission failure is dirty fluid so following these maintenance tips will surely prolong the life of your vehicle and minimize the chance of you needing a major repair.

• Douglas Automotive is at 417 W. Main St., Barrington, (847) 381-0454, and 123 Virginia Road, Crystal Lake, (815) 356-0440. For information, visit douglasautomotive.com. Send questions to underthehood@dailyherald.com.