Replacing the Thermostat

• 1). Raise the front of the Ranger and slide jack stands under the frame rails. Lower the Ranger until only the jack stands support it.
  
  
• 2). Crawl beneath the truck and position a drain pan beneath the radiator petcock. Loosen the petcock by hand and allow all of the coolant to drain from the radiator. Tighten the petcock.
  
  
• 3). Locate the thermostat housing on the lower left side of the Ranger's engine, and position the drain pan under the housing. Loosen the hose clamp holding the heater hose -- the smaller hose -- to the thermostat housing, using a Phillips screwdriver. Pull the heater hose from the thermostat housing.
  
  
• 4). Remove the two thermostat housing-to-engine bolts, using a ratchet and socket, and pull the thermostat housing away from the engine. Use caution, as residual coolant may be in the engine and may flow out when you remove the thermostat housing.
  
  
• 5). Twist the thermostat counterclockwise to unlock it and pull it from the housing. Pull the thermostat gasket from the engine. Scrape any debris from the thermostat-to-engine mating surfaces, using a plastic gasket scraper.
  
  
• 6). Place a thin bead of RTV silicone on the new thermostat gasket and set it on the engine, carefully line up the bolt-holes in the gasket with those in the engine.
  
  
• 7). Install the thermostat in the housing with the spring side facing away from the housing. Twist the thermostat clockwise to lock it in the housing.
  
  
• 8). Set the thermostat housing and thermostat on the engine and hand-tighten the two thermostat housing-to-engine bolts. Torque the thermostat housing-to-engine bolts to 14 to 21 foot-pounds, using a torque wrench and socket.
  
  
• 9). Reinstall the heater hose on the thermostat housing and tighten the hose clamp, using a Phillips screwdriver.
  
  
• 10
  
  Raise the Ranger off the jack stands with a floor jack and remove the stands. Lower the Ranger to the ground.
  
  

Filling and Bleeding the Cooling System

• 1). Start the Ranger's engine. Open the radiator cap and fill the radiator to the base of the filler neck with 50-50 premixed Dex-Cool coolant.
  
  
• 2). Refill the radiator coolant when the level drops. This drop is due to circulation of coolant through the engine. Close the radiator cap and back it off to the first stop, this is the bleeding position for the radiator cap.
  
  
• 3). Set the heater controls to their maximum setting. Increase the engine's rpm to 2,000 and hold it for three to four minutes. Turn the engine off and remove the radiator cap, using shop cloths to protect your hand from the heat.
  
  
• 4). Add 50-50 premixed Dex-Cool coolant to the radiator until the level reaches the bottom of the filler neck and set the radiator cap back to its bleeding position. Start the truck and hold the rpm at 2,000 until the upper radiator hose feels hot, indicating coolant flow.
  
  
• 5). Turn the engine off and remove the radiator cap, using shop cloths to protect your hand from the heat. Add 50-50 premixed Dex-Cool coolant to the radiator until the level reaches the bottom of the filler neck and fully tighten the radiator cap.
  
  
• 6). Remove the cap from the coolant overflow tank and add 50-50 premixed Dex-Cool coolant until the coolant level is between the "Min" and "Max" lines. In total, the Ranger's cooling system holds 1.5 to 1.8 gallons of Dex-Cool coolant.