The Mazda Protege made its debut in 1990. The original Protege was basically a Mazda 323 -- the maker's entry-level car -- with several upgrades. In 1995, Mazda dropped the 323 from its lineup and the Protege remained as Mazda's entry-level vehicle. The 2001 Mazda Protege came in four main trim levels: "DX," "LX," "ES" and "MP3." The "DX" trim level came fitted only with a 1.6-liter, four-cylinder engine. The "LX" trim level came standard with the 1.6-liter, but had an optional 2.0-liter. The "ES" and "MP3" trim levels came only fitted with the 2.0-liter. The engines differ slightly, but the process of replacing the thermostat is the same for both engines.
Raise the front of the Protege with a floor jack and slide jack stands under the vehicle's subframe. Lower the Mazda until only the jack stands support it. Remove the radiator cap.
Crawl beneath the front of the vehicle and locate the drain plug on the bottom of the radiator. Place the drain pan under the drain plug. Remove the drain plug with a ratchet and socket and allow all of the coolant to drain from the radiator. Replace the drain plug and tighten it with a ratchet and socket.
Inspect the lower radiator hose for any defects, such as cracking, sponge-like feeling or visible aging. Replace the hose with a new one if any defects are present. Trace the lower radiator hose toward the engine until you reach the metal housing that connects the hose to the engine; this is the thermostat housing.
Remove the two bolts holding the thermostat housing to the engine with a ratchet and socket. Pull the housing from the engine, exposing the thermostat below it. Grab the thermostat and remove it from the engine.
Scrape the mating surface on the engine and the thermostat housing with a plastic scraper. This assures a clean mating of the two. Do not use a metal scraper, as this can damage the mating surfaces and create a leak.
Place the new rubber thermostat gasket -- included with the thermostat -- around the perimeter of the thermostat. Make certain to line up the small bump on the gasket with the jiggle valve in the thermostat.
Place the new thermostat in the thermostat housing with the spring side facing out. Line up the bump in the thermostat gasket with the notch in the thermostat housing.
Install the thermostat housing and thermostat into the engine and tighten the bolts to 14 to 18 foot-pounds with a torque wrench and socket.
Raise the Mazda with a floor jack and remove the jack stands. Lower the Protege to the ground.
Open the radiator cap and slowly fill the radiator -- at a rate of about 1 quart per minute -- to the top of the filler neck with 50-50 premixed coolant . Open the coolant reservoir and fill it to the "F" mark with 50-50 premixed coolant.
Close the radiator cap and start the Protege's engine.
Run the engine until it reaches normal operating temperature. Increase the engine speed to 2,200 to 2,800 rpm and hold it.
Shut the engine down after holding the rpm steady for five minutes. Allow the engine to cool and check the coolant level in the radiator. If the level is below the base of the filler neck, repeat steps 12 through 14. If the coolant level is at the base of the radiator filler neck, check the coolant reservoir and add 50-50 premixed coolant until the level reaches the "F" mark. The 1.6-liter engine holds 6.3 qts. of coolant and the 2.0-liter holds 7.9 qts. in total.
Take the old coolant to an automotive fluid recycling center. Many auto parts stores perform this service free of charge.
