Read the owners manule.
Buy a kit at auto parts comes with adaptors and instructions
How much antifreeze does a 1998 chevy mabilu ls take
What is the avearage cost to fix a blow headgasket on a 98 lumina
Just did mine on 98 Lumina... low and high side connectors were under air filter chamber box on drivers side. unscrew the top, remove filter, disconnect rubber neck and take our chamber to see AC connectors below. good luck Cat5Cane
Drain the coolant. Follow the top radiator hose to the engine and this is usually where the thermostat is housed. Usually 2 bolts hold the housing on. Pull them and take note of the position of the thermostat, the spring should be engine side. Clean all mating surfaces good or leaking may occur. Reassemble and fill with coolant. Run and check coolant again.
R134A
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On the muffler
You can't, they are bolted in
Coolant for the 98 Deville is added into the coolant overflow bottle. The side of the bottle should have low and high coolant markings.
To replace the water pump on a 1998 Chevy Lumina, first disconnect the negative battery cable and drain the coolant. Remove any components obstructing access, such as the serpentine belt and possibly the alternator. Unbolt the water pump from the engine block, clean the mating surfaces, and install the new pump with a new gasket. Finally, reassemble everything, refill the coolant, and check for leaks.
Most likely because you have added to much coolant when it was cold.