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  1. OSS

    Coolant temp runs hot ALL THE SUDDEN!

    The 2F temperature sender is oriented vertically which traps an air pocket around it. If there’s any frothing going on inside the cooling system from the water pump chewing up bubbles, those micro bubbles will migrate everywhere in the cooling system and coalesce in trapped pockets. The space...
  2. OSS

    Coolant temp runs hot ALL THE SUDDEN!

    Yes but a first start up on a cold engine, the thermostat is closed so any air in the system that burps into the thermostat housing get sucked straight into the spinning water pump and whipped into tiny bubbles. Only when the thermostat opens is “burping” effective. In the end it all works...
  3. OSS

    Coolant temp runs hot ALL THE SUDDEN!

    I think natural purging takes a long time because at first start up of a cold engine that has air in it, the coolant is recirculating inside the engine and not flowing into the radiator. The radiator is a natural air separator, keeping air on top and coolant below, but when the engine is...
  4. OSS

    Coolant temp runs hot ALL THE SUDDEN!

    If the cooling system is opened up to replace coolant, air will get in the system and the temperature gauge will definitely show hot (even on the freeway) for a few weeks until all the air eventually purges out. It can take a long time.
  5. OSS

    Coolant temp runs hot ALL THE SUDDEN!

    The back of the head is the hottest part of the engine. My 2F with a completely overhauled cylinder head and new Toyota head gasket, new 190°F thermostat, new upper thermostat housing, new radiator, new calibrated Toyota temperature sender and a few year old water pump ran approximately 30°...
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