Fan Switch

[timkins]

I just got back from the Nats East at York where I picked up an automatic temperature switch that turns the fan on when the temperature rises to 200 degrees and shuts off at 175 degrees. It is a single wire switch that mounts in the intake manifold near the water neck. My question is concerning the  wiring of the switch. I currently have just an on/off switch with a relay but I would like to install the automatic switch and retain the on/off switch  incase I forget or someone else is driving the car. What would the wiring have to look like to do this.

[MrMopar64]

Here is a rough drawing......... this is why I'm not an artiest    

MM64  

[PeterR]

Just one comment.    In this diagram the feed to the coil runs direct from the battery, and this means after the engine is shut down the signal circuit will still be energised.

Some people like this arrangement because if the engine is really hot the fan will continue to operate until the water cools down even after the engine is switched off.   Others do not like having high current devices runing without the alternator operating to maintain battery charge and prefer to have the coil feed from the ign switch.

If the water temp is just below switching temp sometimes when the engine is turned off the water will creep up just enough to kick in the fan.  No big deal, -but if you happen to have your head under the hood when this happens you will need a change of underwear!!

[MrMopar64]

Just one comment.    In this diagram the feed to the coil runs direct from the battery, and this means after the engine is shut down the signal circuit will still be energised.

Some people like this arrangement because if the engine is really hot the fan will continue to operate until the water cools down even after the engine is switched off.   Others do not like having high current devices runing without the alternator operating to maintain battery charge and prefer to have the coil feed from the ign switch.

If the water temp is just below switching temp sometimes when the engine is turned off the water will creep up just enough to kick in the fan.  No big deal, -but if you happen to have your head under the hood when this happens you will need a change of underwear!!

Oops!......... missed that one......  :oops:

MM64  

[parklane]

No big deal, -but if you happen to have your head under the hood when this happens you will need a change of underwear!![/quote]

what's the matter?? you don't like two toned undies?  

[Roadstar]

My thoughts on the fan running after the engine is off, doesn't actually help cool the engine. It's not circulating anymore so you are only cooling down the water in the radiator.

So in reality all you are doing is draining the battery..

The switch is usually the ground trigger for the relay, So all you need is a toggle switch  wired to the same ground circuit and you can turn the fan on anytime..

[PeterR]

My thoughts on the fan running after the engine is off, doesn't actually help cool the engine. It's not circulating anymore so you are only cooling down the water in the radiator.

Even without the water pump running the water will thermosiphon and remove heat from the engine.  Some of the more senior members (read old farts) will remember engines that did not have a water pump fitted and relied entirely on thermosiphon action for water circulation.