How to Replace a Malibu 1999 Thermostat

by Kevin Mclain

The thermostat on the 1999 Chevrolet Malibu regulates the engine's temperature. The thermostat has a temperature-sensitive spring that causes the thermostat to open and close as the temperature of the coolant changes. This process keeps the engine block at a safe temperature by allowing the coolant to circulate through the engine when needed. When the engine is running, the thermostat stays closed until the engine temperature reaches the operating temperature. The thermostat then opens and allows the coolant to circulate. If the thermostat sticks, change it immediately.

Pull the 1999 Chevrolet Malibu into a safe work are that has a level surface. Set the emergency brake and open the hood. Allow the engine to cool down completely. It will generally take at least an hour or more for the engine to cool down, depending on how hot it was before you shut it down.

Check the radiator cap for pressure and heat after the engine has cooled down. If there is no pressure or heat on the cap, unscrew it from the radiator to relieve any coolant pressure off the radiator hoses.

Locate the air filter intake box on the driver's side of the engine. Remove the intake box by unscrewing the small bolts from the inside of the box with a 3/8-inch drive ratchet, extension and a socket. Pull the intake box off and place it to the side. The thermostat housing on the engine block can now be accessed.

Slide the fluid catch pan underneath the Malibu in the general location of the thermostat housing to catch any excess coolant that spills out of the thermostat housing or the radiator hose.

Follow the top radiator hose from the top of the radiator to the thermostat housing tube on the engine block. Remove the hose clamp from where it secures the radiator hose to the thermostat housing tube by loosening the clamp adjustment bolt counterclockwise with a flat-head screwdriver. Pull the clamp about 6 inches back onto the radiator hose.

Twist the radiator hose back and forth until it loosens from the thermostat housing tube. Pull the hose straight off the tube.

Locate the two mounting bolts on both sides of the thermostat housing. Loosen and remove the two bolts by turning each bolt counterclockwise with a metric open-end wrench.

Pull the thermostat housing straight up off the engine block and place it on a clean rag. Pull the thermostat straight up out of the engine block.

Scrape away any of the old gasket that might remain on the base of the thermostat housing or the engine block with a flat scraper. Wipe away the old gasket from the thermostat housing and the engine block with a clean rag. Continue wiping both surfaces until they are both completely clean.

Position the new thermostat housing gasket onto the bottom of the housing. Push the two mounting bolts through the housing to hold the gasket in place. Lower the housing back over the engine block and screw the two mounting bolts into the top of the engine block until both bolts are tight. Finish tightening both bolts down evenly with the open-end wrench to properly seat the new gasket.

Reattach the top radiator hose to the thermostat housing tube. Slide the hose clamp back over the hose and the tube. Tighten the clamp with the flat-head screwdriver until the hose is completely tightened to the thermostat housing tube.

Add coolant to the radiator if necessary to completely fill up the radiator. Screw the radiator cap back on and tighten. Crank the engine and let it run for about three minutes or until the engine reaches operating temperature. Inspect the thermostat housing gasket and the radiator hose for any leaks with the engine running. Turn the engine off.

Tip

  • check Be sure to tighten both of the thermostat housing mounting bolts down evenly so that the gasket will properly seat to the top of the engine block and the base of the thermostat housing. This will prevent any leaks around the new gasket.

Warnings

  • close Wear gloves and safety glasses if necessary when replacing the thermostat.
  • close Use caution when working around hot coolant or a hot engine. A hot engine or hot coolant can cause serious burns.
  • close Always wait for the engine to completely cool down before attempting to remove the radiator cap.

Items you will need

References

About the Author

Kevin Mclain has more than 20 years of automotive, home improvement and landscaping experience. He has been writing for various online publications since 2002. Mclain has U.S. Army certification in automotive maintenance and repair, among more than 15 additional certifications related to the automotive field.