How to Change a 98 Tahoe Thermostat

The thermostat inside the 1998 Chevrolet Tahoe controls the antifreeze coolant from getting into the engine block until the thermostat has reached the preset temperature setting on the thermostat spring. A stuck thermostat can prevent the antifreeze coolant from getting into the engine and cause the engine to overheat. If the engine gets extremely overheated, it can actually crack the engine block, and then you will need a new engine.

Instructions

1

Park the truck and let the engine completely cool down before replacing the thermostat. Once the engine has cooled down, remove the radiator cap from the radiator.

2

Locate the radiator drain plug underneath the radiator on the driver side of the radiator. The drain plug will have a small handle attached to the plug. Slide the fluid catch pan underneath the radiator plug. Loosen the radiator drain plug with the pliers. Turn the drain plug counter clockwise slowly. The looser that the drain plug is, the more fluid will flow from the plug. Allow all of the antifreeze coolant to drain into the fluid catch pan.

3

Move to the top of the engine and locate the top radiator hose. The other end of the top radiator hose is attached to the thermostat housing. The thermostat housing is attached to the intake manifold on the very front of the engine. Remove the thermostat housing with a ratchet and a socket. Leave the radiator hose attached to the thermostat housing elbow. Pry upward on the thermostat housing with a flathead screwdriver and the thermostat housing will come off.

4

Pull the thermostat out of the intake manifold. Discard the old thermostat into the fluid catch pan.

5

Remove the old thermostat housing gasket from the thermostat housing and the thermostat housing insert on the intake manifold. Use the flat head scraper to remove any hard to remove gasket material. Wipe the surfaces clean with a rag.

6

Insert the new thermostat inside of the intake manifold with the spring on the thermostat facing downward inside of the intake manifold. The spring must be facing downward inside of the intake manifold or it will be in backwards and not work.

7

Apply a thin bead of the red high temperature silicone onto the thermostat housing gasket. Then press the gasket in place onto the thermostat housing insert on the intake manifold. This will prevent the gasket from moving while you are attaching and tightening the thermostat housing down.

8

Slide the thermostat housing back over the thermostat onto the intake manifold insert. Line the bolt holes up and screw the bolts back in place. Tighten the bolts down very tight with the ratchet and socket. The proper tightening torque on the thermostat housing bolts is 20 ft-lbs., as recommended by the Chevrolet Tahoe Owners Manual. You can buy a torque wrench at nearly every auto parts store.

9

Crawl back under the front of the car and tighten the radiator drain plug back tight. Then start adding 50/50 antifreeze coolant to the radiator until the radiator is full. Once the radiator is full, crank the engine up. Let the engine run until you can visually see the antifreeze level start to drop inside of the radiator. This means that the new thermostat is opening and allowing the antifreeze into the engine.

10

Keep adding antifreeze to the radiator while the engine is running until the fluid level stabilizes at the top of the radiator fill cap. Inspect the radiator drain plug and the thermostat housing for leaks as the engine is running. Once that the antifreeze fluid level has stabilizes and there are no leaks, put the radiator cap back on.