But does anyone have a good understanding of how the thermostat can control the engine temperature when it's reading the output from the radiator? It seems like the thermostat would have to have a much different opening temp than the engine temp you were shooting for since the coolant the thermostat is seeing has been cooled by the radiator already. It also seems like the radiator output temp would be able to vary a lot even with engine output temp staying the same.
The FZ's coolinng system sends coolant out the front of the block. The large hose feeds the radiator, the small hose feeds the oil cooler (heat exchanger). When the cooling system is operating under the thermostat's opening temperature (whatever that is), the thermostat is closed. Therefore, flow through the radiator is minimal and is limited to the bleed through/around the thermostat. During this operation, the coolant circulates mostly from the engine, to the oil cooler, through the thermostat housing, and back to the water pump for circulation to the engine. Once the engine and oil cooler sheds enough heat into the coolant, the thermostat opens and the bulk of the cooling system flow is directed through the radiator.
So...limiting bypass through the thermostat and/or reducing airflow through the radiator will speed up the cooling process. Atypical perhaps, but that is how it currently operates.
With my experience working on Japanese cars, the thermostat does not have an accurate read of the temperatures between the radiator and engine. Not sure what its called, but there is an element in the thermostat that reacts to the temperature of the coolant on the engine side. When this element (someone here help me out) reaches its rated temperature it causes the thermostat valve to open up and allow the radiator coolant to cycle through into the engine. Each thermostat element is selected by the engine designers to accommodate the engine its going into.
The gauge cluster and ECU gets its temperature reading from a temp sending unit connected to the engine, typically in the same area of the thermostat. Its possible to have a defective sending unit giving you and ECU inaccurate temp readings even though the actual engine temps are on target.
The cooling fans also operate on a separate temp sensor usually located on the radiator.
So in short, there are many layers to the cooling system of an engine that need to be investigated.
The 'element' you are speak of are commonly waxes that are designed to soften at specific temperatures. When it softens, the thermostat opens. Most cars (and engines that I've been into) use the thermostat to block the flow of coolant to the radiator until the engine reaches operating temperature. There are a few exceptions, but the bulk I've worked with operate as such. The FZ-09 is an exception.
The temperature sensor is located in the back of the cylinder head (facing the rider). I don't think any non-Yamaha employees are privy to the coolant jacket routing at this time, so unsure where the sensor is reading in relation to the cooling system diagram. At any rate, this is the sensor that commands the fan's operation. There is no temp sensor in the radiator.
Not that it helps us...but the Super Tenere runs cool, as well...
