Overheating Cavalier—plugged heater core
Owners of GM 2.4 engines may encounter overheating problems that drive them crazy. If you’ve checked the thermostat, water pump, and radiator and still can’t find the cause, pressure clean the heater core. That’s right, the heater core. This engine setup uses returning coolant from the heater core to open the thermostat. GM wants the heat to get to the heater core first. If the heater core is plugged, the thermostat never sees hot coolant.
To confirm that you are dealing with a plugged heater core, simply install a piece of heater hose to bypass heater core and drive the vehicle. If the engine stops overheating, you’ve nailed the problem.
To flush the heater core, attach two pieces of heater hose and use a garden hose on low pressure to backflush. The hose that comes from the top of the engine is the inlet hose to the core, so attach the fresh water to the other (outlet) hose. Run the drain hose into a bucket. Also, backflush the “H” hose that’s installed.
That should solve your overheating problem.
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© 2007 Rick Muscoplat
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