How to Replace Thermostat 98-12 Ford Ranger 4.0L

Difficulty: Intermediate · About 60 min · Ford Ranger

Replace the thermostat and bleed the cooling system on a 1998-2012 Ford Ranger with the 4.0L engine.

Steps

1. Drain the coolant

   Remove the radiator cap, remove the four 10mm bolts holding the under-radiator cover and pull it down, have a drain pan ready, open the drain plug with a 19mm wrench, let it drain, then hand-tighten the plug.

2. Remove the intake tube

   Remove the throttle body cover's Phillips screws and 7mm bolt, loosen the two intake hose clamps and the air box clasps, then remove the intake tube and box.

3. Remove the upper radiator hose

   Remove the alternator's 13mm bolt and move the wiring harness, have a drain pan ready, compress and slide back the hose clamp nearest the radiator and twist the hose off, let it drain, then compress and slide back the second clamp to free the hose from the water pump.

4. Remove the old thermostat

   Remove the thermostat cover's three 8mm bolts, remove the cover, then remove the thermostat.

5. Install the new thermostat

   Insert it into place, press on the cover, then tighten its three 8mm bolts.

6. Reinstall the upper radiator hose

   Tighten the alternator wiring bracket's 13mm bolt, connect the hose to the water pump and tighten its clamp, then connect it to the radiator and tighten that clamp.

7. Reinstall the intake tube and bleed the system

   Insert the tube and air box cover, tighten the hose clamps with a flat blade screwdriver, reconnect the breather hose and MAF sensor, refit the throttle body cover and its screws, refit the lower cover and its 10mm bolts, then fill the radiator with coolant, run the engine with the fan on low and heat on high while topping off coolant, and refit the cap once bubbles stop and heat flows from the vents.

Check your vehicle’s repair manual for exact specifications and fit.