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Hi guys,
I have fitted electric fan and I am going to connect it to the sensor in the head (1256) Does anybody know what the operating temperature of this sensor should be? I assume it should work at a lower temperature than the one currently fitted so as to stop the car over heating?
Also does anybody know the thread size?
Thanks for your help!

First of all you can't use the sensor on the head for two purposes. You must have 2 sensors, one for the temp gauge and one for the fan. Secondly, the fan will require a thermocouple type sensor which operates a relay to switch on the fan. Thirdly, the fan is there to cool the water in the radiator and the sensor should be fitted on the rad or at least in one of the pipes connected to the rad, usually the top hose. If you take the temperature behind the thermostat the fan will switch on before any hot water reaches the radiator.

https://www.ebay.co.uk/itm/AeroLine-Adj ... SwHjNV8Tt9

This is the type I've used in the past and it works very well. The thremocouple tube is placed inside the top hose at the joint with the radiator and the joint sealed with some silicone gasket sealer. You will need a relay wired in as well, this will operate the relay for you.

Or, you could mount the fan on the front of the radiator as a pusher type fan, retain the existing fan and operate the electric fan manually with a switch when you see the temp gauge rising too high.

I've seen some that are a short length of solid pipe with a threaded hole for the thermo sensor switch.

Does it work OK in the top hose, as that only has water flowing when the thermostat is open? All the ones I've seen on the OHC engine seem to be fitted there, and I wondered if that was the best place, or just the only place it'll go.

As it happens I had this discussion today with a friend at a show. One thought is that hot water rises to the top and therefore the fan switches on when the top of the rad is hot whether the water is flowing through the hose or not. It also picks up the temperature of the hot water just as it leaves the engine, if it was way above the stat temp then it needs extra cooling before it goes back into the engine.

In theory the engine does not need additional cooling provided by the fan when the thermostat is closed.

The other thought, is that a sensor in the bottom hose picks up the temperature of the water already cooled by the rad before it enters the engine. If the water is too hot the fan switches on and adds more cooling. It could be that this position is preferred by manufactures as it has better potential to keep the engine at optimum temperature for economy etc.

Our discussion came to the opinion that the top position was a good idea as it could be monitored by the temp gauge and closely reflected the actual engine temperature. This would make it easier to set up accurately on a DIY basis. When you see the gauge getting too high set the sensor to switch on.

Whereas, the sensor in the bottom hose more accurately senses the engine needs but as the temp gauge is reading the other end of the cooling system is more difficult to use as a DIY guide in the setting up process.

We finally concluded that there was probably not much difference really nor any big advantage in either position. The top hose sensor would be set at a temperature a bit above the thermostat temperature and the bottom hose sensor would be set somewhat below thermostat temperature.

Now the caveat..... these were our 'sitting in the sunshine at a car show theories' and not founded on research.

Well, that's probably more thought than I've given it. I think the OEM fan sensor on my modern is in the radiator somewhere, so one of the hoses is probably as close as you can get without modifying that.

1972nail wrote:https://www.ebay.co.uk/itm/AeroLine-Adjustable-Electric-Car-Fan-Thermostat-Universal-Fitting/191209768780?hash=item2c84fd874c:g:nWIAAOSwHjNV8Tt9

This is the type I've used in the past and it works very well.

I just ordered one of those plus a 7" fan to put on the front of the rad