this is for the 5.0 engine
http://media.Photobucket.com/image/serpentine%20belt%20diagram%2097%20mercury%20mountaineer%205.0/brian123dye/SANY0172.jpg
Check the main crank pulley.
Check the condition of the accessory drive serpentine belt, belt idler pulley and belt tensioner pulley bearings.
There is a tensioner located towards the front of the engine. You'll need a fairly long handle ratchet, a breaker bar preferred. In any event you'll have to determine what on your model has to grab a hold of, release the tension and slide the belt off of which ever pulley is close. Then relaese the tension SLOWLY!!! there is a lot of tension on it and it could snap out of your hand. then reverse the process only retract the tensioner at the end when your ready to put the belt on your last pulley.
Look on the passenger front side of the engine, you will see pulley attached to a short arm with a square hole. That is the tensioner and tensioner pulley
right side of crankshaft pulley
You don't. The pulley is pretensioned by the manufacturer. If the belt tension is incorrect, the pulley must be replaced.
You don't. The serpentine belt tension is automatically maintained by the tensioner pulley, which is an idler pulley located on the passenger side of the system and looks like it doesn't drive anything. If the belt tension is incorrect, the tensioner pulley must be replaced. If the question meant 'how to release tension from the belt' (for removal, etc.), this is done by applying the correct size socket wrench to the tensioner pulley's center nut and rocking the pulley away from the belt.
If you are referring to the Serpentine belt, you loosen no pulley. You simply remove tension from the belt. The tension is applied by the Idler Pulley. Pry the idler back and remove the belt.If you are referring to the Serpentine belt, you loosen no pulley. You simply remove tension from the belt. The tension is applied by the Idler Pulley. Pry the idler back and remove the belt.
put it on the tension srewand push back towards muffler
The tension pulley should have a bolt that holds it on, allowing you to replace the unit.
When looking form the passenger side of the car the tension pulley is on the right hand side. It is the one located in the middle of the "column" (second one down slightly indented to the left)
It will be one of the smooth ones with no ribs.