How to Replace the Thermostat in a 2002 Oldsmobile Alero

by Justin Cupler

Despite its newcomer status, the Alero was the final Oldsmobile to roll off the century-old automaker’s assembly line. The final 500 Aleros were special-edition models that included distinctive interior and exterior trim in commemoration of Oldsmobile’s storied history. The 2002 Alero has quite an interesting process to replace the thermostat on its base-level 2.2-liter engine. When equipped with a manual transmission, the process is a pretty much a straightforward remove and install. But with an automatic transmission, you must remove the exhaust manifold to create the clearance needed to remove the thermostat housing just to gain access to the thermostat.


Proceed directly to Step 4 if your Alero has a manual transmission.


Remove the three bolts securing the heat shield to the exhaust manifold, using a ratchet and socket, and remove the heat shield. Remove the oxygen sensor from the exhaust manifold with a ratchet and oxygen sensor socket. You do not need to disconnect the oxygen sensor, simply set it aside.


Raise the front of the Alero with a floor jack and slide jack stands under its frame rails. Lower the Olds onto he jack stands. Crawl beneath the vehicle and find where the exhaust flex pipe connects to the exhaust manifold. Remove the three flex pipe-retaining nuts from the manifold’s studs using a ratchet and socket. Pull the flex pipe rearward to clear the manifolds studs, then downward to disengage it from the manifold.


Raise the vehicle off the jack stands with the floor jack and remove the jack stands. Lower the Alero to the ground.


Unscrew the cap from the Alero’s coolant overflow tank. Position a drain pan under the petcock on the bottom of the radiator. Turn the petcock counterclockwise until it stops to begin the flow of coolant from the radiator. Once the coolant stops flowing, tighten the petcock. Proceed to Step 7 if your Alero has a manual transmission.


Remove the eight exhaust manifold-to-cylinder head nuts with a ratchet and socket, and pull the exhaust manifold from the engine compartment. Pull the exhaust manifold gasket from the cylinder head and discard it. Clean the mating surface on the cylinder head and manifold with a plastic gasket scraper.


Look on the middle of the engine block on the passenger’s side and find the metal housing bolted to the water pump housing; this is the thermostat housing. Remove the two bolts, securing the thermostat housing.


Push the thermostat housing and hose forward to expose the thermostat below it on an automatic transmission Alero. On Aleros with a manual transmission, pull the thermostat housing and hose upward to expose the thermostat. Pull the thermostat from the water pump housing.


Install the rubber seal around the perimeter of the new thermostat if it’s not pre-installed from the box. Guide the thermostat into the water pump housing with the spring side facing out of the water pump housing.


Reposition the thermostat housing over the top of the thermostat and hand-thread the two thermostat housing bolts. Tighten the two thermostat housing bolts to 2 foot-pounds using a torque wrench and socket. Proceed to Step 17 if the Alero has a manual transmission.


Slide a new exhaust manifold gasket onto the exhaust manifold studs on the cylinder head. Install the exhaust manifold onto its studs on the cylinder head and hand-thread its retaining bolts. Tighten the exhaust manifold bolts to 9 foot-pounds, starting from the top center nut and working outward, using a torque wrench and socket.


Lift the Alero and slide jack stands under the subframe. Lower the Alero onto the jack stands.


Pull the old gasket from the groove inside the flex pipe and set a new gasket into the groove. Guide the flex pipe flange onto the studs on the exhaust manifold and hand-thread the retaining bolts. Tighten the flex pipe bolts to 26 foot-pounds with a torque wrench and socket.


Raise the Alero off the jack stands and remove the jack stands. Lower the vehicle to the ground.


Apply a thin coat of an anti-seize chemical to the threads of the oxygen sensor and hand-thread the sensor into the manifold. Tighten the oxygen sensor with a ratchet and oxygen sensor socket.


Set the exhaust manifold heat shield onto the exhaust manifold and hand-thread its retaining bolts. Tighten the heat shield bolts to 18 foot-pounds with a torque wrench and socket.


Add 50-50 premixed Dex-cool coolant to the overflow tank slowly until the level reaches and stays consistent at a level at the top of the coolant overflow tank’s label. Tighten the coolant overflow tank’s cap.


Start the engine and increase the rpm to between 2,000 and 2,500 until it reaches operating temperature – roughly halfway up the temperature gauge. Allow the engine to idle for three minutes and shut it off.


Allow the engine to cool until it is cool to the touch. Check that the coolant level is still at the top of the coolant overflow tank’s label. Add more 50-50 premixed Dex-cool coolant as needed. The 2.2-liter engine has a total coolant capacity of 2.15 gallons, but the exact amount required to fill it may vary.


Take any old coolant to a nearby automotive fluid disposal center. Some auto parts stores take old fluids free of charge.


  • Engine coolant is highly toxic, and its sweet taste and smell may attract young children or animals. If they mistakenly consume it, it may cause severe illness and even death, so keep children and animals away from your work area and always store coolant safely.

Items you will need

About the Author

Justin Cupler is a professional writer who has been published on several websites including CarsDirect and Autos.com. Cupler has worked in the professional automotive repair field as a technician and a manager since 2000. He has a certificate in broadcast journalism from the Connecticut School of Broadcasting. Cupler is currently studying mechanical engineering at Saint Petersburg College.

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