Mustang GT V8-4.6L SOHC VIN X (1998)
Thermostat: Testing and Inspection
When investigating a concern of overheating or an insufficient heater/defroster performance, perform the following:
1. Check and service any leaks in the:
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radiator cap.
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pressure relief cap.
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heater hoses.
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radiator hoses.
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water hose connection gasket.
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head gasket.
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water pump housing gasket.
2. Check the cold engine coolant level in the radiator.
a. If the engine coolant level is low, fill with proper coolant concentrate. Add coolant concentrate to the degas bottle to the FULL COLD mark.
b. If the cold engine coolant level in the degas bottle is sufficient, run the engine for 10 minutes with the pressure relief cap on. Check for coolant
circulation through the heater and radiator hoses. If the coolant drops below the FULL HOT mark, add coolant to the filler neck. Repeat the
above procedure until all the air is purged from the cooling system.
When this procedure has been completed, feel the heater inlet and outlet hoses and the underside of the upper radiator hose. The water
thermostat should be removed only if these hoses are cold after 10 minutes of operation.