The Nissan Patrol's automatic serpentine belt tensioner assembly consists of a tensioner hub, tensioner arm and tensioner pulley. The pulley rides on the serpentine belt, applying the tension provided by the spring-loaded tensioner arm. Inside the pulley is a bearing ring that allows the pulley to spin freely as the belt moves across the pulley's surface. The main cause of pulley failure is bearing damage, which can either lock the pulley in place or fail to keep it aligned with the serpentine belt. The tensioner pulley itself is not serviceable apart from the tensioner assembly, so you'll need to replace the entire assembly to change the tensioner pulley.
Open the Nissan Patrol's hood and hold it open with the prop rod. Note the position and location of the automatic belt tensioner on the face of the engine as illustrated on the serpentine belt diagram, which you'll find on the fan shroud.
Rotate the Patrol's automatic tensioner off the serpentine belt using the serpentine belt tool. Pull the serpentine belt out of the tensioner pulley path with your other hand while slowly rotating the tensioner back into position.
Unbolt the automatic belt tensioner from the Patrol's front engine cover using a socket set. Lift the old tensioner assembly out of the Patrol's engine well by hand.
Place the new automatic tensioner on the front engine cover by hand. Thread the bolts through the automatic tensioner and into the front engine cover by hand. Tighten the automatic tensioner bolts with a socket set.
Reinstall the Patrol's serpentine belt in the reverse sequence of how you removed it. Close the Patrol's hood.
