PlumbingThe cooling system in most cars have a lot of plumbing. We'll start at the pump and work through the system. In the next sections we'll get into more detail about each part of the cooling system. >
The pump sends the fluid into the engine block, where it makes its way through passages in the engine around the cylinders. Then it returns through the cylinder head of the engine. The thermostat is located where the fluid leaves the engine. The plumbing around the thermostat sends the fluid back to the pump directly if the thermostat is closed. If it is open, the fluid goes through the radiator first and then back to the pump.
There is also a separate circuit for the heating system. This circuit takes fluid from the cylinder head and passes it through a heater core and then back to the pump. On some cars there is a heater control valve that opens up to allow the fluid to flow when the temperature is set to hot.