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Electrically Heated Thermostat
Model specific variants of the electrically heated thermostat are now equipped on all LEV/
ULEV compliant engines. This thermostat allows the engine to run hotter than conventional
thermostats improving fuel economy.
The ECM also electrically activates the thermostat to lower the engine coolant temperatures
based on monitored conditions. It is both a conventionally functioning and ECM controlled
thermostat (two stage operation). ECM control adds heat to the wax core causing the thermostat
to open earlier than it’s mechanical temperature rating providing increased coolant
flow.
Conventional Function: The thermostat begins to open at 103ºC. This is at the inlet side of the water pump and represents the temperature of the coolant entering the engine. Before the 103ºC temperature is realized, the coolant is circulated through the engine block by the water pump.
After the temperature reaches 103ºC it is maintained as the inlet temperature by the thermostat. The coolant temperature at the water pump engine outlet is approximately 110ºC. The additional 7ºC is achieved after the coolant has circulated through the block.
The operating temperature of the engine will remain within this range as long as the engine is running at part load conditions and the engine coolant temperature does not exceed 113ºC.
ECM Control
Electric thermostat activation is based on the following parameters:
• Engine temperature > 113ºC
• Radiator Coolant Outlet Temperature
• Load signal “ti” > 5.8 ms
• Intake air temp > 52ºC
• Vehicle speed > 110 MPH
When one or more of these monitored conditions is determined, the ECM activates
(switched ground) the thermostat circuit. The activated heating element causes the wax
core in the thermostat to heat up and open the thermostat increasing coolant circulation
through the radiator which brings the engine temperature down.
The temperature of the coolant at the inlet side of the water pump will drop to approximately
85ºC and the temperature at the outlet side will drop to approximately 103ºC when activated.