overheating

[jezzeroo]

corsa cooling fan not coming on when engine is hot

[Cockney_si]

How hot is "hot", is the engine actually in need of cooling from the fan?

If yes check water is hot in header tank first as water may not be circulating round the engine.

Most cars have a thermostat that usually screws into the radiator and has a two-core wire coming from it.

It can usually be tested by unscrewing it and dipping the end in a shallow bowl of hot water. (Don't put wire in)

If it's working then then the fan should spin up.

Of course the cooling fan fuse may have gone, or the top radiator top hose valve may have gone.

[Tim Baxter]

Additionally you will need to know the temp at which your rad sensor opens/closes.  My last car (Corsa 1.2)ran at 90 deg C and I'm under the impression that you need to get it hotter to operate the fan.  Because the cooling system is pressurised it is possible to (marginally) exceed 100 deg C without boiling over.  Check a Haynes or workshop manual.

KEEP FINGERS CLEAR BECAUSE SOME FANS BURST INTO LIFE WHEN IGNITION IS OFF.

Be careful when 'unscrewing' rad sensor as it may need a plastic seal/gasket when you replace it.

Yes, check your fuse.

If fuse OK, apply 12V direct to the fan to make sure it's working.  I had a diesel Montego which never got hot enough for the fan to run.  Consequently when the engine did overheat I discovered that the fan had rusted to death and siezed ages before.  Bye bye engine.

[marcus5771]

If there are two wires comming out of the sensor join the together then you would know the is power and also a good earth. Dont worry the two wires are in fact earth wires.

[Tim Baxter]

I think that what Marcus5771 is saying is short circuit the two sensor wires together to bypass it and provide 12v to the fan.  Fair enough.  BUT, It makes no sense whatsoever to have 2 earth wires coming out of the sensor, think about it!!!!

[marcus5771]

You have to find by the fan working that soon the engine will cool if it does then the swicth is faulty. Most switches are earth switches. One wire is earth then the sensor switches earth to the other wire thus switching on the fan.          

[Tim Baxter]

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