1994 Toyota Corolla engine coolant temperature fluctuate

1994 TOYOTA COROLLA
140,000 MILES • 4 CYL • FWD • AUTOMATIC
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JOHNZ002
  • MEMBER
  • 1 POST
I have a Toyota Collora 94DX 1.8L, 140000 miles. After I start engine, let it idle for 5 minutes, the engine temperature rises to the middle of the meter on the dashboard, heat comes out of the heater, very warm. Therefore I think the thermostat, water pump are working properly. But when I start to drive, the temperature immediate drops to zero, no more heat comes out of the heater. What are wrong? Thank you.
Jan 7, 2010 at 2:50 PM
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MMPRINCE4000
  • AUTOMOTIVE REPAIR CONTRIBUTOR
  • 8,548 POSTS
The thermostat is open.

The thermostat and heater are independant of each other, in other words the heater does not depend on the opening/closing of thermostst for heat.

However, if thermostat stays open all the time when you start moving, the airflow through radiator cools the coolant causing temp to fall, since thermostat is not closing allowing temp. to increase.
Jan 8, 2010 at 7:53 AM