To replace the serpentine belt on your G35's engine, you'll have to put in a little extra work. You have to remove the coolant reservoir, driver-side air-filter housing and the radiator cooling fans to gain enough clearance to remove the belt. You won't need special tools, but you will need a 1/4-inch thick keyway bar or metal rod to complete the procedure.
Work only on a cold engine. Until you disconnect their wiring harness, the cooling fans can turn on unexpectedly, even with the ignition off.
Loosen the radiator cap a quarter-turn to relieve the pressure, then tighten the radiator cap. Clamp the overflow hose shut with locking hose clamps or pliers. Remove the overflow hose from the radiator neck. Remove the bolt that secures the coolant reservoir to the fan shroud, then remove the reservoir and overflow hose from the engine bay.
Loosen the clamp that secures the air intake tube to the driver-side air filter housing, using a Phillips screwdriver. Remove the air intake tube from the housing. Disconnect the wiring harness from the MAF sensor.
Remove the bolt that secures the air filter housing to the vehicle. Pull upward on the housing with a slight tug, then remove it from the engine bay. Disconnect the wiring harness from the cooling fan control module. Remove the two upper mounting bolts for the cooling fan assembly.
Lift the front end of your G35 with a floor jack. Place jack stands under the subframe rails, then lower the G35 onto the jack stands. Support the engine shield by hand, then remove the retaining bolts. Lower the shield and place it aside. Support the cooling fans by hand, then remove the two lower nuts. Lower the fan assembly and remove it from under the vehicle.
Make a drawing of the serpentine belt routing or snap a reference photo with your smartphone. Insert the head of a 3/8-inch-drive ratchet into the square hole on the tensioner arm. Rotate the arm counterclockwise as far as it can go. Slide a piece of 1/4-inch-thick keyway bar or similar item into the locking boss at the top of the tensioner arm, then remove the ratchet. Remove the serpentine belt.
Turn the tensioner pulley, idler pulley and all of the accessory pulleys by hand. If any exhibit resistance or make noise, replace them before continuing.
Route the belt around the pulleys according to the drawing you made earlier. Rotate the tensioner counterclockwise slightly, then remove the keyway bar from the locking boss. Slowly release the tensioner arm to apply tension to the belt. Inspect the belt position on each pulley. Adjust the belt as needed so that it sits within the outer ridges of every pulley.
Install the fan assembly to the radiator. Install the two lower nuts and tighten them. Install the engine undercover and snug the bolts. Lower the G35 to the ground.
Install the upper fan mounting bolts and tighten them. Connect the wiring harness to the fan control module. Press fit the air filter housing into place, then install the two mounting bolt. Slide the air intake tube onto the air filter housing and tighten the clamp. Connect the wiring harness to the MAF sensor.
Install the coolant reservoir to the fan shroud. Install the mounting bolt and tighten it. Connect the overflow hose to the radiator neck, then release the hose clamps.
Start the engine and shut it down. Look at the indicator on the top of the tensioner assembly. The notch on the tensioner arm should be between the two notches on the stationary base of the tensioner pulley. If the notch on the arm sits outside of the notches on the base, replace the tensioner.
