Variable speed rad fan

[shokenore]

Here is one for the electrical gurus.
2.4 radiator fan, the one controlled by the thermo switch under the thermostat.
The fan will randomly start and stop with no regard to coolant temp.
The fan will also vary its speed going from pulsing on off to a fairly low speed to full speed.

If I apply battery power to it the fan is at full speed.
If I remove the thermo switch the fan speed is full speed.
If I stick a meter on the thermo switch contact spade I get 5 volt to earth.

I'm assuming that the fan feed to the relay is earthed out via the thermo switch making the circuit, so would a sticky relay give me the 5 volts at the thermo switch?

Ta

[NiftyNev]

Not sure of an answer as to what is faulty. Maybe just the thermo switch. You do know that the switch is a normally closed type?

Nev.

[BUSHWHACKER]

Deteriorated or heat damaged wiring at the thermo switch.

[NiftyNev]

Remove the thermo switch wire and ground it. I fan remains off then suspect fault switch. If it still does funny things look at the wiring or relay.

Nev.

[shokenore]

Deteriorated or heat damaged wiring at the thermo switch.

Remove the thermo switch wire and ground it. I fan remains off then suspect fault switch. If it still does funny things look at the wiring or relay.

Nev.

I took the spade connector off and it ran at full speed, and earthing against the thermostat body turns it off.

I think I have a spare switch in the garage somewhere it is not the right range (93-88 ) but will be ok to test with but at least with the winter we have forecast it might not get that hot anyway.....
This will be the third thermoswitch that I have changed in as many years, I gues this is why the Toyota one is £80 and the intermotor one is £8.


I couldn't work out why the fan would speed up and then slow down though ?