Coolant Thermostat Control

Reacting to coolant temperature, wax in the wax element expands or contracts. This opens and closes the ball rotary valve in the coolant thermostat housing. [Temperature range: approx. 98 - 108°C (208.4 - 226.4°F)] Furthermore, by distributing power to the coolant thermostat heater element, the ball rotary valve is opened and closed according to engine requests. ECM controls the thermostat heater element by closing the circuit according to the operating conditions (characteristics map). The coolant thermostat operates as follows, according to coolant temperature and control performed by ECM.

• Close
• Start opening (mix mode)
• Open (cooler mode)

CLOSE

The ball rotary valve is closed under the following conditions.

• Engine coolant temperature: 95°C (203°F) or less
• Coolant thermostat heater element: No power distribution
• No full load request

In the closed position, coolant circulates in the engine. Coolant flows to the heater core, if necessary, but not to radiator. This increases coolant temperature rapidly and accelerates warm-up, improving fuel economy and reducing toxic exhaust gas.

Courtesy of NISSAN NORTH AMERICA, INC.

	Coolant thermostat housing
	Wax element
	Coolant thermostat heater element
	Ball rotary valve
A	From engine
B	To radiator
C	To heater heat exchanger

START OPENING (MIX MODE)

The ball rotary valve opens according to the following conditions.

• Engine coolant temperature after engine start (no full load request): reaches 98°C (208.4°F)
• Coolant thermostat heater element: power distribution

In the range of coolant temperature approximately 98°C - 108°C (208.4°F - 226.4°F), the wax in wax element is expanded or the wax element is heated by distributing power to coolant thermostat heater element . This opens ball rotary valve and coolant flows to the radiator. The degree of the opening of ball rotary valve changes according to wax temperature or coolant temperature. This adjusts the coolant flow to the radiator.

Courtesy of NISSAN NORTH AMERICA, INC.

	Coolant thermostat housing
A	From engine
B	To radiator
C	To heater heat exchanger

OPEN (COOLER MODE)

When coolant temperature is 108°C (226.4°F) or more, the ball rotary valve opens fully, allowing the maximum amount of coolant to flow to the radiator.

When coolant temperature is 85°C (185°F) or more under the full load request condition, ECM fully opens the ball rotary valve by controlling the thermostat heater element to heat the wax element. Accordingly, the maximum amount of coolant flows to the radiator.

Under the following conditions, coolant temperature is adjusted to prevent it from reaching the hazardous temperature range.

• Intake air temperature: 38°C (100.4°F)
• Engine speeds: 3, 000 RPM or more
• Engine load: 30%

ECM circulates coolant to the radiator to lower the coolant temperature by controlling the coolant thermostat heater element and opening the ball rotary valve according to ambient temperature. When ambient temperature is less than 12°C, ECM adjusts coolant temperature at approximately 90°C (194°F). When ambient temperature is 12°C (53.6°F) or more, ECM adjust coolant temperature at approximately 80°C (176°F).