The HD and FD (Elantra and Elantra Touring) have the same engine and automatic transmission and similar design of the radiator (which has the tank on the sides of the radiator rather than the top and bottom of the radiator. Each can have the aux trans cooler installed.

Materials
Hayden 1401 aux transmission cooler kit
3 feet of transmission cooler hose and extra clamps
1 quart of SP-III fluid

Tools
Nut driver or screwdriver
set of wrenches/sockets
Hose cutter or pair of dikes
Jack or pair of ramps

1. Raise front end of car with jack/stands or ramps.

2. Remove the lower splash guard under the front bumper. Also remove the fan by pulling it out of the 4 clips. The 2 top clips have a lock so you will need to pull the tab to lift it out of the clip.

Note: removing the grille is impossible without removing the bumper. The grill is screwed to the bumper from behind and accessing the screws is very difficult with the bumper installed.

3. Attach the cooler hoses (uncut) to the cooler and tighten clamps. This makes it easier to get them on.

4. Mount the cooler to the radiator in a vertical position where the hoses are on the bottom. Mount the cooler high enough so you can route the hoses toward the drivers side of the car without having them droop below the crossmember and kinking them. Use the instructions in the kit to do this.

5. There is a small plastic/rubber flap on the lower part on the drivers side next to the radiator. There is a hole in it. Route the hoses into that, and up to an existing hole in the radiator core support.

6. The cooler hose you want to remove is the lower cooler hose on the radiator. Although this is the feed line, all electronically controlled transmissions are monitoring the temperature of the transmission and the transmission will shift erratically if the temperature is below 160 degrees or the CEL will turn on when the ATF temperature reaches 215 degrees. You want the ATF to be between 155 and 195 degrees. I found if the aux cooler is hooked up to the feed line will not overcool the transmission, whereas if it was connected to the return line, it can overcool the transmission.

7. Once the hose is disconnected from the radiator, you could remove the other end from the transmission, which is beside the stock airbox. Removing the rigid intake tube from the airbox makes it easier to do this.

8. Attach one cooler hose from the aux cooler (leave enough slack for engine movement) to the lower radiator cooler port. Attach the other cooler hose to the transmission feed line port on top of the transmission. Tighten clamps.

9. Lower car to level ground and check fluid. Add trans fluid if necessary. On both the HD and FD, the dipstick will show a higher level and lower level depending on which side you look at. This is caused by the dipstick rubbing against the side of the dipstick tubing at the tranny. Use the lower level to check the fluid.

10. Drive car for about 20 minutes and recheck the fluid. Turn off engine, wait about 5 minutes (this will burp air from the system) and recheck the fluid while the trans is in neutral on level ground. The fluid should be at the top hot line. Add fluid if necessary to reach that level.