electronic fan stays on


Full member
gto twin turbo
Hi guys, i havent been on here for a long time, in fact it's been a year & im going to put the GTO TT 1991 back on the road for summer.
The problem i have is the electronic fan stays on nearly all the time, i changed the coolant last year but that didnt help (does anyone know if this system has to be bled, if so where is the bleed nipple) i was told that there is a sensor that that could also be related to the fan staying on but cant remember which one :confused:
Can anyone help or advise, any info appreciated D.D.D
Countrybumpkin is your man, but IIRC he is away for a bit. It does sound like a temp sensor that has failed.
Look if there is any Thermoswitch in the top tank of radiator. In a car with thermoswitch controlled fan, the thermoswitch will be solely responsible. If the fan is controlled by ECU then check the Coolant Temperature Sensor.
Have a multimeter? Then just find out the normal resistance of these sensors of your particular car from the manufacturer's site or manuals. Then just check the resistance of those as given in the manual. It's the easiest way I can imagine for diagnosing the problem for those who do not have much knowhow on internal parts. get back with the results...
And once again, you can check the Thermoswitch by checking it's continuity with multimeter. A Thermoswitch will not allow to complete a circuit in normal temperature. Hope you can test continuity...
The Thermostat, or thermo-switch is basically a bimetalic strip with two metals, which expand at a different rate when a temperature is applied to it.

Now if you use a multimeter, and it shows a 0 ohms resistance or you could simply wire a diode, or a 12 volt bulb into a series with the current being supplied from the battery, and it lights up, then its the thermostat at fault, because the bulb/ diode should light up only after heat is applied to the actual bi-metalic strip.

So just go ahead and change.

If the light does not come on, apply heat to it with the help of either a lighter,( the flame kind, not your lighter from the car). if it turns on after the heat, then there could be one of two things.

Either the temper of the strip has deteriorated, or there is a short from the battery side.

Then take the continuity connector and check the battery side of the connection. If you get a light then the problem, is with the thermstat, because if there was a short before that point, i.e. at the thermostat connector,the circuit wud be complete before the connection and there would not be a +ve and -ve pole for the bulb/ diode to light up.

Again change the thermostat or thermo-switch.

If its none of the above, then mebbe you need a new car?...............; ;) ;) ;)

Just kidding!

Try your local Auto-shop.

Lemme know how it goes.............
On the early models the fans are controlled by two sender units in the bottom of the radiator, main fuse box side.
On later models 93 onwards, they are controlled by a temp sender in the thermostat housing which triggers the ECU to switch them on/off.

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