AO Gold Member
Join Date: Jun 2007
Location: United Kingdom
Re: How Hot???
The thermostat controls the flow of water. When the water temp is hot it will open, to circulate through the radiator and the engine. When it is cold it will close to allow the engine to reach operating temperature, and bypass the radiator. This process is repeated to maintain the correct temperature of coolant.
If (as I assume is the case) the thermostat is stuck open, cold water is constantly flowing around the engine and radiator, and never reaching the correct operating temp. This will cause higher fuel consumption, and can eventually (over a long period) be detrimental to the engine.