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Message: <blockquote data-quote="bimmerman" data-source="post: 100682" data-attributes="member: 126">Hey Mr Captain America! So glad to hear from you!! I think you're right. Might as well change the water pump and thermostat.Here's what i've been up to earier.....I changed the thermal switch pictured here. For those who don't know, the job of the thermal switch is to turn on the auxilary fan when the coolant temperature approaches 100 degrees celcius.Notice the red, black and brown wires on the connector? If you remove the connector and short out red and brown you get speed 1 on your auxiliary fan and if you short out black and brown you get the other speed. You have to turn your ignition on to do this test and my auxiliary fan tested out ok.So after installing the switch i took the car out for a few hot laps including some tail out action and then let her idle. Was it the thermal switch that was faulty? Is the problem solved you asked?No! It's not solved. Within 10 minutes the temperature began to rise towards the 3/4 mark again. The thermal switch did not even acivate the fan meaning the coolant temperature at radiator level was not even up to temperature to activate the aux fan. So i unplugged the thermal switch connector and shorted the earlier described wires to manually activate the fan at full speed for 3 minutes and the temperature did not even come down meaning that it's not a radiator or fan issue anymore.Now the only suspects left are the thermostat, the water pump or air trapped in the cooling circuit.The upper radiator hose felt hot to the touch and the lower hose felt warm. This indicates that there is circulation from radiator to engine block and back to radiator but could it be that the flow is insufficient to cool the engine? Looks like Mr E34Touring is absolutely right!Where does the temperature gauge get it's reading from anyway?</blockquote>

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