Do you put transmission fluid in with the car on or off

By Tom Morr

Vehicles' vital fluids normally perform two important functions: lubricating and cleaning. As the fluid circulates through the parts, it gathers the dirt and metal shavings that can accumulate over time. If you're lucky, this debris will settle on the bottom of the pan or housing and not circulate through the system. That’s why some auto shops use machines that perform a transmission fluid flush, ensuring that more of this debris is removed before any new transmission fluid is poured into the vehicle.

Nothing prolongs vehicle life more than regular fluid changes. In automatic transmissions/transaxles, the recommended service interval is about every 30,000 miles or 30 months. (Check your owner's manual or service manual for your car's specifics.) The automatic transmission fluid (ATF) should be changed sooner if its dipstick reveals dark or burnt-smelling fluid.

DIY transmission fluid and filter changes

Even those of us who change our own oil often cringe at the prospect of draining ATF. Because many transmission pans don't have drain plugs, changing the fluid can be a messy proposition –the entire pan must be removed. But even on vehicles that do have drain plugs, the pan still must be removed to change the filter.

Changing transmission fluid is one of those messy jobs that someone has to do. Doing the deed yourself will save money, possibly time and fresh ATF can make your gearbox perform young beyond its years. It’s also relatively easy to determine when your ATF may be low. Consider an automatic transmission service if you detect the following signs of low transmission fluid:

Transmission slips
Transmission shifts roughly
Noisy transmission
No drive engagement in forward or reverse gears

How to change automatic transmission fluid: Step-by-step instructions

If you can garner some initial patience, learning how to change automatic transmission fluid will only benefit you in the long run. More importantly, you’ll need an automatic transmission filter kit; they normally contain a gasket for the pan in addition to the new transmission filter and its O-ring. Along with some basic shop tools, you’re ready to get started.

Step 1: Transmission fluid drains better at operating temperature, so let your car idle for a few minutes first. After turning your ignition off, raise and secure the vehicle. Then, lay down a tarp, some cardboard or a newspaper under at least a two-gallon catch pan. Next, remove the bolts from one side of the transmission pan, being cautious of hot exhaust parts and fluid.
Step 2: Gradually loosen the other bolts, which should allow the pan to tilt and begin to drain. Once all bolts are removed, lower the pan and dump the remaining fluid into the catch pan. Gently break the gasket seal with a screwdriver, if necessary.
Step 3: Clean the gasket surfaces on both the pan and the transmission housing. Inspect the pan for metal shavings or other signs of internal damage, and then clean it with solvent.
Step 4: Remove the old transmission filter and O-ring. The filter contains fluid, so keep the drain pan underneath.
Step 5: Install the new transmission filter, making sure that its O-ring seats in the appropriate orifice.
Step 6: Attach the new gasket to the pan with oil-soluble grease –not gasket sealer or adhesive.
Step 7: Refer to the service manual about using thread sealer on any or all of the transmission pan bolts, then screw in all fasteners finger-tight.
Step 8: Torque the pan bolts to spec in a spiral pattern starting at the center. Maximum torque is often about 12 pounds per foot.
Step 9: Lower the vehicle and fill the transmission with the recommended amount of fluid.
Step 10: Start the vehicle, warm it up, then shut it off and check for leaks. If you don’t detect any leaks, run the vehicle up to operating temperature on level ground, move the shifter through all gears, return to park and check the dipstick while the engine idles.

Always practice good safety behaviors when working on motor vehicles. To help prevent injuries, use appropriate personal protective equipment, which may include safety gloves, goggles, helmets and shoes.

Your transmission is just as important as the engine in your vehicle. Without it, your car may be able to start but will go nowhere fast. Keeping your transmission in good condition is vital and as with any major component on your vehicle, protection begins with maintenance. Checking your transmission fluid levels, color, and even scent will help you understand what condition your transmission is in. Regular flushes and good habits such as using your parking brake when stopped and shifting to drive from reverse only at a complete stop are great ways to help extend the life of your transmission. Not sure how to check your transmission fluid? Follow our quick reference guide!

The transmission fluid dipstick is similar to the oil dipstick, while the oil dipstick measures the level of the car’s engine oil, transmission dipsticks measure the level of transmission fluid in your vehicle. Keep in mind many transmission troubles are due to low fluid levels. If the fluid is low, it is likely there is a leak and it will need to be found and repaired by a professional right away. If you need to add additional fluid, be careful not to overfill the reservoir. Overfilling transmission fluid can cause the fluid to foam, putting excess pressure on the transmission, and forcing fluid out of the vent or a seal. This can result in slipping and instability.

Park your car on a level surface and lift the hood.
Turn on your car, leaving it in park, and let the engine run for a few minutes to warm up. Transmission fluid expands in heat and in order to receive accurate results, it must be under normal operating conditions. If the fluid is checked when the engine is cold, you may get false results indicating the fluid is low. Allow the engine to continue running while you check the level. Note: Honda is the only manufacturer that recommends you turn off the engine and then immediately check the level.
Locate your dipstick. Often found near the oil dipstick in front-wheel drive vehicles and near the rear of the engine for rear-wheel-drive engines, it is conveniently labeled for access and can have a red, pink, or yellow-colored handle.
Pull out the dipstick and using a clean rag, wipe it clean, and place it back into the reservoir. Remove the dipstick again and locate the indicators on the stick to determine whether the fluid is “full” or “low.” If the fluid is full, replace the dipstick and close the hood. If the fluid is low, take your vehicle to an auto center right away for a fill.

Things to Look For When Checking Your Transmission Fluid

Color – Most new transmission fluids should be a bright, transparent red color. Darker red or light brown is normal but reflects its age and usage. A darker brown color is an indication that fluid needs to be changed. Black is a bad sign, however. This means that the fluid is burnt as a result of some transmission troubles. Your vehicle should be taken to a transmission specialist to determine the cause of the burnt fluid, immediately.
Consistency – After some time fluid can appear thicker than usual. This is normal, but good transmission fluid should appear new. Additionally, fluid should not contain any contaminants or particles including metal shavings. Metal shavings could spell trouble and will need to be inspected right away. Foamy fluid could indicate either too much fluid is present, it is overheating, or the wrong fluid has been added.
Smell – Clean fluid is practically odorless, but if you notice something similar to burnt toast, it is cause for concern. A burnt smell is a sign that the transmission has developed problems and needs to be serviced by a professional right away.

NOTE: Many newer cars are not equipped with transmission dipsticks, making checking the transmission fluid at home impossible. In that case, an automotive repair professional will need to check the fluid level through a plug located on the side of the transmission or by checking the car’s internal computer.

How Often Should You Check Transmission Fluid?

Arizona has a hot, dry, and dusty climate defining it as a “severe driving climate.” In severe climates, vehicles require a little more TLC, meaning maintenance services should be performed on a more frequent basis. Transmission fluid flushes should be performed every 30,000 miles and transmission fluid levels should be checked, at least every six months. Now that you know how often to check your transmission fluid and the steps on how to do so, you’re one step closer to extending the life of your transmission!