Does anyone know the trick to install new belt. It is correct length. I could even reinstall the old one. It didn't seem to come off that hard.

 

You need to use a ratchet wrench to pull up on the automatic belt tensioner (that's the small pulley at the top; use the nut on its face to turn it counter-clockwise). This relieves the tension on the belt and allows for easy positioning. Then make sure to correctly route the new serpentine belt around all the pulleys, and release the belt tensioner.

 

Make sure you follow the belt routing diagram that's in the engine compartment. I've seem some people spend a huge amount of time trying to figure out how it routes around the water pump. Use the diagram...