It is true to say that the fan must run when the temp gauge gets to more than half way. If you are overheating then you must first check the fan is good.
Removing the connector to the fan switch (located on bottom right of radiator,between hoses on rad), put a thick wire across pin contacts of this connector. This simulates a closed switch i.e. fan should run. Test should be done with engine running. If fan does not run this is either a dead fan or you have no power or bad earth and you still need an auto electrician to test further. If fan runs then it could mean that the temperature switch fitted to the radiator could also be faulty.
Assuming the fan is running with the wire connected to the connector of the fan switch , then check to see if temp gauge goes down and car cools down. Do not leave the wire in place , replace connector to switch after test.
A simple test for the thermostat operation is to start engine from cold and run up to heat. During the warm up touch test the bottom hose and the top hose leading to the radiator. The bottom hose should warm up and get hot almost 5-10 minutes after starting engine. The top hose should feel cold until the engine gets hot (half way or more on temp gauge) and then will almost suddenly get warm to hot in less than a few seconds. This indicates the thermostat is opening correctly. If top hose remains coldish then thermostat is stuck shut , not allowing water to flow into the radiator and thus car overheats.
I had renault clio 1.4 today which was running very hot with temp gauge warning light on and needle at the top i.e. engine is overheated . After letting engine cool down and releasing excess pressure (carefully) I removed the two bolts to the thermostat housing and found that a high temp thermostat had been fitted which was marked as 98 degrees , the replacement unit from Renault was marked as 91 degrees opening. After fitting and testing the engine heated to correct level and every now and then fan would operate for a short period to keep engine temp gauge to about half way with no overheating. SO in this case although there was no fault with the original thermostat ,it was just the wrong type. I think this was fitted because there was very little heat from the heater matrix and so I think someone put a hotter running thermostat to get more heat. Unfortunately this was the wrong thing to do. In fact the heater matrix was totally blocked and the only solution is to replace it, but at least I now have a stable engine temp and thermostat and fan are working together as they were designed. HTH
George / Go-Cool Services/Bristol UK, November 2008
