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Changing Transmission Fluid

Considering most people drive the same roads every week—going to work, the grocery store, school, what have you—it’s fairly easy to detect an issue when your gear shifts aren’t as subtle or smooth. If you suspect the issue is the transmission, you can check by pulling out the dipstick from the car’s auto transmission, the fluid for which is red with a noticeable petroleum smell when fresh. If the fluid is low, looks like linoleum in color, smells distinctly awful, or all of the above, your car’s transmission fluid needs to be changed.


If your transmission is having problems, inspection is your first move. Low fluid levels could mean there is a leak in the system somewhere, potentially from a cooler line running to the bottommost part of your radiator. Find it, fix it, or hire someone else to, before topping off the level. It should only take roughly a pint to go from the “Add” to “Full” marks. If you are lucky, your shifting or lagging issue could disappear after adding transmission fluid. However, if the fluid has a dark, smoky color or a burnt odor, an entire change is needed.

Fresh Fluid

To avoid incredibly expensive transmission repairs, the best thing to do is change the transmission fluid regularly, specifically in 30,000 mile intervals, though if you often pull heavy loads during hot weather, annual changes may be the better option. The first step is to remove the transmission pan and then the old filter. However, up to half of the old transmission fluid and the contaminants within it are inside the torque converter, the valve body, the clutch drums, and other places. So, to do this yourself, you need to work at it a bit more.

No matter how far you want to go, you have to get the transmission pan off. Once your car is secure on ramps and the wheels blocked, find an appropriate pump, run a pickup hose through the car’s dipstick tube until the hose bottoms out, and pump until no fluid comes out. This should reduce your spillage.

Now, for extracting the rest of the old transmission fluid, keep the pan on, take out a trans cooler line at the radiator, set a drain pan underneath it, and then start the engine for some moments to see where the fluid’s flowing. Attach a smaller hose to either the radiator outlet or the line connector to gather the fluid. Put the hose into a large jug and let your engine run until air spurts. Then, remove the transmission pan, so you can change the filter and its seal and wash sediment and deposits from the pan. When you reinstall the pan, start every bolt by hand for two threads before tightening them.

Luckily, for those who wish to keep it simple, a trans flush and refill is a service your local mechanic can do for a fee, but be sure of the quality of the service they offer. Some places simply attach a machine to your cooler line, change out the fluid, and call it a day, but make sure the transmission pan is taken off for cleaning.

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Photo via Chatchai Kritsetsakul / Shutterstock