type53b wrote:My car seems to run a bit hot at the moment. The gauge is sitting about 3/4 of the way up after about 20 minutes driving but I am not fully convinced it is overheating. I fitted a new gti rad, flushed the cooling system, filled it up with g12 and as far as I can tell I bled it correctly. It doesn't lose or leak coolant. The level never varies. There is no oil in the coolant tank. Could it be, that she is at normal temperature but the gauge is reading high? If so how do I test the gauge and sensor ?
The gauge can be tested. If you disconnect the wire at the sensor, and connect the wire to earth through a variable resistor, here is what you should see:
With a resistance of 40 ohms, you should be at the full hot side of the gauge.
With a resistance of 258 ohms you should be at the full cold side.
The service manual allows for one needle width of deviation from full hot or full code with these resistances.
These measurements are made with the engine running.
VW has a simple tester for this, but you can use also use a variable resistor or potentiometer. That being said, I'd be surprised if the gauge it bad. I think it would be more common for the gauge to not work at all. I'm not sure if the senders themselves go bad - again I would sort of think if they fail, they fail altogether. The service manual says if the gauge is good, but your reading is bad, replace the sender.