Fresh transmission fluid smells like normal petroleum and is light red in color. Old transmission fluid turns a darker and darker brown until it gums up into a sludge-like material, eventually making your entire transmission system struggle through its operations. It will also begin to carry a stale and scorchy smell, depending on how long it is left to deteriorate. The transmission fluid in your 2004 Hyundai Elantra should be changed every 25,000 to 35,000 miles, which is when you are most likely to begin seeing changes in the appearance and smell of the liquid.
Purchase three quarts of transmission fluid from your local Hyundai dealer. Other fluids can potentially harm your transmission system, so it is essential that you use only the Hyundai-specified fluid for your Elantra.
Drive your Elantra for at least 10 minutes before beginning the transmission fluid replacement. This allows the fluid to heat up and drain more easily than if it were at air temperature.
Engage your Elantra's emergency brake to prevent potential hazards as you work on and under the hood of your car.
Turn your car off so to prevent accidental sparking or injury.
Raise your Elantra's front end using a car jack. Jack stands are recommended for extra support, and the stands should be locked by their security bar. You may want to wiggle your car before getting under it to be sure that the vehicle is being adequately supported by the stands.
Open your hood and disconnect the tube that connects the transmission and radiator. This can be accomplished by gently unclamping the tube with your adjustable wrench. Exercise caution in this step, since the transmission fluid will be extremely hot.
Place the line into a drain pan for safety purposes, as small amounts of fluid will seep from the tube during the transmission-fluid changing procedure.
Get under your Elantra and find the metal plate that is fastened by several bolts, securing the transmission drain pan to the transmission itself.
Remove the bolts from the drain pan using an 8 mm hex socket, allowing the drain pan to catch any extra fluid that falls from the transmission area during this step.
Wipe the drain pan clean using your dry shop rag. Do not moisten the shop rag, as water or cleaners could damage the transmission.
Replace the drain pan, re-bolting it with the hex socket. Do not over-tighten the bolts, since this could damage or even cut through the drain pan.
Remove the jack stands by releasing the safety bar and pulling the stands out from under your vehicle.
Lower the car jack cautiously, as your transmission-fluid line is still sitting open with the drip pan under the hood of your car.
Remove the black cap from the transmission-fluid port, which is located next to the dipstick.
Position your funnel into the entry of the fill port and slowly begin pouring each quart of transmission fluid until the fluid has reached the fill line. If you are unable to see the fill line, the dipstick can be used to check the fluid level. The Elantra's fill capacity is slightly less than three quarts, so the amount needed will depend on how much fluid was left in the container after the drain-pan process.
Close the hood of the vehicle and remember to change your transmission fluid again in 25,000 to 35,000 miles.
