How to Change a Thermostat in a Chevy Blazerby Jody L. Campbell; Updated November 07, 2017
Items you will need
3/8 inch Drive ratchet
3/8 inch Drive 10 inch extension
3/8 inch Drive socket set
Antifreeze drain bucket with handles and spout
2 gallons of replacement Dex-cool or global antifreeze diluted
Replacement thermostat and gasket
Despite the intimidating first impression of the thermostat in the Chevy Blazer, it's not overly difficult to replace it. It is a messy job no matter what steps you perform to prevent it. If you haven't had a coolant flush or drain-and-fill service done in some time, it would be a good idea to drain and fill your radiator while you're replacing the thermostat.
Park the Blazer on the flat surface and release the hood latch. If the engine is hot or even warm, allow time for it to cool down. Open the hood and brace it on the hood prop.
Remove the radiator cap slowly.
Place the drain bucket beneath the radiator drain cock and open it to drain the radiator. To access the drain cock, you will have to crawl under the Blazer. Allow the radiator to drain below the thermostat level or drain the radiator completely. Retighten the drain cock.
Locate the thermostat. It is near the alternator. If you follow the upper radiator hose, it runs from the driver's side of the radiator up across the engine, and back around over the engine to the middle of the block near the alternator.
Remove the plastic heater hose clip from the lower thermostat bolt head. Remove both thermostat bolts using the ratchet, extension and a socket. Separate the thermostat from the engine. It will spill some leftover antifreeze, so hold it upward and try to support it under some other engine components to allow the contents of the hose drain back into the radiator.
Remove the old thermostat and clean the flange of the upper and lower thermostat housing using the gasket scraper. Clean this very thoroughly. Any debris or leftover gasket could cause a leak in the coolant system.
Insert the new thermostat and gasket and replace the bolts. Tighten the bolts thoroughly with the ratchet, extension, and socket. Replace the plastic heater hose clip to the lower thermostat bolt head.
Fill the radiator with 50% Dex-cool or Global antifreeze until full. This will take a while and air pockets in the radiator will occasionally burp and create room for more antifreeze. When the radiator will take no more, start the engine with the radiator cap still off of the radiator. Place the drain bucket below the radiator neck, and allow the Blazer to run until operating temperature is achieved, adding more coolant to the radiator as necessary.
Check the heat inside the Blazer and keep an eye on the thermostat gauge on the instrument panel. Once the heat is working, the gauge is up to temp (190 degrees) and the radiator is full, shut off the Blazer and replace the radiator cap. Fill the overflow reservoir with remaining coolant to the full mark.
Remove the drain bucket and hose down the antifreeze spillage from the engine and any spillage on the ground. Wipe well with shop rags. Antifreeze has a sweet smell and taste that will attract young children or animals and is very poisonous. Close the hood and pour the spent antifreeze into the empty containers the new antifreeze came in, and dispose of properly.