How to Replace the Thermostat in a '97 Four-Cylinder Ford Ranger

The Ranger has manned the front line for Ford since 1983, drawing young buyers to the Ford truck lineup with hopes of eventually converting them to the F-series. The 1997 model year was the final one for the 2.3-liter four-cylinder engine, following a 14-year run as the base-level engine. The thermostat on the 2.3-liter Ranger regulates the coolants flow from the engine into the radiator. Once the coolant reaches between 180 and 195 degrees F, the thermostat starts opening to allow coolant to flow into the radiator to be cooled. Replacing a failed thermostat on the 1997 Ranger requires you to bleed the cooling system upon completion.

Instructions

Allow the truck to sit until its engine is cool to the touch. If you recently drove the truck a long distance, this may take several hours.

Wrap your hand in a thick shop cloth to protect it from potentially hot coolant. Slowly unscrew the cap from the radiator.

Raise the front of the Ranger with a floor jack and slide jack stands under the trucks frame rails. Crawl under the truck until you have a clear view of the bottom of the radiator. Find the radiator petcock drain plug on the bottom of the radiator.

Position a drain pan under the petcock and twist the petcocks thumbscrew counterclockwise to start the flow of coolant from the radiator. Once the flow stops, twist the petcock clockwise to close it.

Raise the truck off the jack stands with a floor jack and remove the jack stands. Lower the Ranger to the ground, leaving the drain pan under the thermostat housing to catch any residual coolant.

Remove the heater hose the smaller one from the passengers side of the thermostat assembly by loosening its hose clamp with a flathead screwdriver and pulling the hose away from the thermostat housing with a slight twisting motion.

Find the engine coolant temperature sensor on the thermostat housing. Pry upward and hold the locking tab on the ECT sensors wiring harness with a flathead screwdriver, then unplug the harness from the ECT sensor.

Loosen the hose clamp securing the upper radiator hose to the thermostat housing, using a flathead screwdriver. Pull the upper radiator hose from the thermostat housing with a slight twisting motion.

Unfasten the two bolts securing the thermostat housing to the cylinder head, using a ratchet and socket, and pull the housing from the cylinder head. Pull the thermostat and the thermostat-housing gasket from the cylinder head.

Scrape the gasket-mating surfaces on the thermostat housing and cylinder head with a plastic gasket scraper, then wipe both surfaces off with a clean, lint-free cloth.

Apply a bead of a sealing compound meeting Ford specification ESE-M4G115-A to the new thermostat-housing gasket. Press the thermostat-housing gasket onto its mating surface on the cylinder head, aligning the bolt holes on the gasket with those on the cylinder head.

Guide the thermostat into the cylinder head, spring side first. Slightly rotate the thermostat right or left until you feel it seat in the grooves in the cylinder head,

Set the thermostat housing back into place on the cylinder head and hand-thread its retaining bolts. Tighten the thermostat housing bolts to between 14 and 21 foot-pounds with a torque wrench and socket.

Press the upper radiator hose into its inlet on the thermostat housing and tighten its hose clamp with a flathead screwdriver. Press the heater hose into the inlet on the side of the thermostat housing and tighten its hose clamp with a flat-head screwdriver.

Fill the radiator to the base of its filler neck with 50-50 premixed ethylene glycol (green) coolant. Wait about five minutes as the coolant settles and displaces air. Add more coolant as needed to bring the level to the bottom of the radiators filler neck.

Tighten the radiator cap onto the radiator, then loosen it to just its first stop this is the caps bleeding position.

Turn the Rangers heater temperature and blower fan to maximum. Start the Rangers engine and hold the rpm at 2,000 for between three and four minutes. Turn off the engine.

Wrap your hand in a thick shop cloth to protect it from hot coolant and steam and carefully remove the radiator cap. Add more coolant as needed to bring the coolant level to the bottom of the radiator filler neck.

Repeat Step 3. Start the engine and hold the engine speed at 2,000 rpm until the temperature gauge reaches about the halfway point. Using a cloth to protect your hand, carefully remove the radiator cap and add coolant to bring the coolant level to the base of the radiator filler neck if needed. Tighten the radiator cap.

Lift the lid from the coolant overflow bottle. Using a clean turkey baster, siphon out as much old coolant from the overflow tank as possible. Add just over 1 quart of 50-50 premixed ethylene glycol (green) coolant. Close the coolant overflow tank cap.