How to Change the Thermostat on a '91 Ford Ranger

A properly working thermostat can add years to the life of your Ranger.

Your 1991 Ford Ranger has been a workhorse for years, and you'd like to see just how many more miles and years you can get out of it before you purchase a new truck. Checking the oil, rotating the tires and making sure you use premium gas are helpful measures--but if that couple-dollar thermostat stops working, all your work may go down the drain. A bad thermostat can cause a warped engine block and a few thousand dollars in repair bills. Add a little insurance to your Ranger: Replace that worn-out thermostat.

Things You'll Need

• Flat-head screwdriver
• 10 mm wrench
• Cotton towel
• Razor blade
• RTV gasket maker
• 1991 Ford Ranger thermostat

Instructions

1. Trace the radiator hose that extends from the top of the radiator to the intake manifold on top of the engine. The metal housing that the hose connects to on the intake manifold is called the thermostat housing. Remove the radiator hose from the thermostat housing by prying the hose retaining clip off the radiator hose with a flat-head screwdriver. Pull the hose off the housing, and lift it up to drain the radiator fluid back into the radiator.

2. Remove the two bolts that hold the thermostat housing onto the intake manifold of the Ford Ranger, using a 10 mm wrench. Keep the bolts; you will reuse them. Pull the thermostat housing off the intake manifold.

3. Pull the old thermostat out of the intake and discard it. You will not reuse it again.

4. Scrape the old thermostat gasket off the bottom of the thermostat housing and off the intake manifold, using a razor blade. Plug the hole left behind by the thermostat, using a towel. This will prevent getting any of the gasket into the engine.

5. Place a bead of RTV silicone onto the bottom of the thermostat housing and allow 20 minutes for the silicone to firm up.

6. Place the new thermostat into the intake manifold. It sits on a machined lip just below the level of radiator fluid in the hole.

7. Bolt the thermostat housing back onto the intake of the Ranger, and secure the radiator hose back onto the housing using the original retaining clip.

Tips & Warnings

• It is common to use a band clamp instead of the original retaining clip when reinstalling the radiator hose onto the thermostat housing. A band clamp evenly distributes clamping pressure around the hose. This minimizes the chance of leaking from the radiator hose.

References

• Haynes: Ford Ranger Repair Manual 1983 to 1992
• Auto Media: Changing a Thermostat