Golf GTI L4-1984cc 2.0L DOHC (9A) (1990)
Thermostat: Testing and Inspection
THERMOSTAT QUICK-CHECK:
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A thermostat that is stuck open will cause the engine to warm up slowly and run below normal temperature at highway speed. A thermostat that is
stuck closed will restrict coolant flow to the radiator and cause overheating.
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To quickly check if the thermostat is opening and if coolant is circulating through the radiator, allow a cold engine to reach operating temperature (
temperature gauge needle approximately centered). Feel the radiator hoses. If the hoses are hot to the touch, the coolant is circulating. If the hoses
are not hot, coolant flow to the radiator is probably restricted. Check for a faulty thermostat or a plugged radiator.
THERMOSTAT BENCH TEST:
Testing Thermostat
Thermostat
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Heat in water:
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Starts to open at approx.: 87°C (188°F).
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Fully open at approx.: 102°C (215°F).
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Opening stroke: 7 mm (0.28 in) minimum.