Transmission fluid is a petroleum-based product that provides lubrication, viscosity and power to the transmission of a vehicle. The fluid helps cool the friction created between the moving internal metal components. After time, the fluid will break down and lose its chemical properties. In addition, small metal flakes from the moving components will begin to contaminate the fluid. Checking the fluid is important between change intervals and is fairly simple to do. Because different vehicles employ variations to checking the transmission fluid, a maintenance service manual for your vehicle or a repair manual should be obtained.
Read the service maintenance manual or the repair manual before attempting to check the transmission fluid. While many vehicles require warming the vehicle up to operating temperature and then leave idling when checking the fluid, some import vehicles require the opposite.
Park the vehicle on level ground. The slightest angle can offset the fluid level and give you a false reading. If the manual suggested leaving the vehicle in park with the engine idling, do so. Release the hood latch and apply the parking brake.
Open the hood and locate the dipstick for the transmission fluid. The transmission bolt to the back of the engine, so the dipsticks are most often located on the lower back side of the engine and can be located on either the left or right side. Some dipsticks will stamp the word "Trans Fluid" on them, some feature a red handle--opposed to the yellow engine oil dipstick handle--and others may be the same color as the engine oil dipstick.
Pull the dipstick out of the dipstick tube and wipe it off thoroughly with a shop rag. Look at the bottom tip of the dipstick to learn which reading the dipstick employs. Some dipsticks use a small crosshatch design--about an inch long--while others use notches or lines to indicate full and low fluid readings. The low marking will still be a safe reading for operation, but below the low line would indicate the transmission needing fluid.
Reinsert the dipstick into the dipstick tube and be sure to replace it in its seated position with the bottom of the handle contacted the top of the tube. Extract the dipstick once more to get the fluid level reading. If the engine is running, be sure not to be wearing loose clothing or dangling jewelry that can come into contact with moving engine parts.
Examine the end of the dipstick again to determine the level reading. Transmission fluid is rarely low unless a leak is apparent in the system. The color and smell of the fluid is equally a determinant that it might be time to change the fluid. Dark brown and burned smelling fluid indicates the chemical properties of the fluid is compromised. Inspect the level of the fluid. If it's between the full and low line, the fluid level is okay.
Adjust the level of the transmission fluid, if necessary, using a funnel. With the dipstick tube extracted, place the funnel into the dipstick tube. Pour a small amount of transmission fluid at a time and allow it to drain thoroughly down into the transmission. Vehicles that require the engine to run, still need to be running when adding fluid. Recheck and add more if necessary.
