Jeep Thermostat

My son has a 1999 Jeep Grand Cherokee 6 cylander 258. We need to replace the thermostat and are unable to release the belt tensioner. Is there a special tools or is it something simple.

You may need something like this to gain access to the belt tensioner. http://www.toolsource.com/stinger-serpentine-belt-tool-p-97503.html?sourceid=nextag

Tester