Obstructed Coolant Flow

Possible locations or causes of obstructed coolant flow are as follows:

• Inoperative water pump
• Inoperative engine thermostat (stuck or sticking closed)
• Pinched or kinked heater hoses
• Improper heater hose routing
• Plugged heater hoses or supply and return ports at the cooling system connections
• Plugged heater core or heater core tubes

If proper coolant flow through the engine cooling system and heater core is verified, and heater outlet air temperature is low, a mechanical problem may exist.