Cooling fan switch

[peters3103]

G’day all
I’ve fitted an SU fan switch into my header tank.
On at 80 off at 70. Car runs at just under 70 on the gauge. Clearly the new switch is too low as the fan comes on too early and stays on ages after the engine is switched off. I have one that I ordered from Coolcat along with my fan. It’s on at 85 of at 80. Too high? I note the alternative SU fan switch listed for the E-Type is on at 90 off at 80. Any experiences here?

Pete

[Philk]

Hi Pete

As a baseline, I would attempt to get an independent reading on the header tank temperature since the water gauges are often inaccurate. If an independent temperature check shows the otter switch is working properly, you could manually adjust the gauge from the internal adjuster mechanism so it reads more accurately.

One thing you mentioned is the fact that the fan runs on after the engine is switched off - that is not normally the case and means the fan is wired in to the permanently live part of the harness.

I have a Fosseway solid-state otter switch (possibly the equivalent as the Coolcat) which I find very good. For hot weather driving (possibly more of an issue for yourself than us here), I also have a manual override wired in to the fan circuit so, if I see that I'm about to join a queue on the motorway (which means the fan would definitely come on a few minutes later), I can pre-empt that by switching the fan on early.

[Moeregaard]

Personally, I wouldn't be bothered by the fan coming on at 80C/176F and turning off at 70C/158F. This is keeping the engine temp in a good place and nowhere near running too warm. Since the original Otter switches were notorious for failing, I always felt lucky that mine tended to turn the fan on at 70C, rather than not at all.

Both of my E-Types had temp gauges that were right on the money, but Phil makes an excellent suggestion regarding the accuracy of yours. He also makes a good point about having your fan wired into a permanently live part of the harness. There's no reason to do this, and it often leads to a flat battery.

[peters3103]

Thanks for your replies/suggestions. The fan is wired correctly and does switch off after about 10 mins as it takes that long for it to cool to the off temp of the switch presumably. The car was fitted with a Kenlowe fan previously and had the Kenlowe controller with the copper wire running into the top hose - not ideal and used to leak. Now fitted with the Coolcat fan I decided to remove the Kenlowe controller and revert to the switch in the header tank. I’ll try fitting the Coolcat switch (on at 85 off at 80) and see how that goes. I’ve never had overheating issues with the car. Also looking at buying the Revotec manual override switch kit.

[Philk]

The location of the override switch (and its visibility) is very much down to personal choice. I kept mine out of sight (simply to avoid altering the appearance of the dashboard) and placed the switch next to the trip meter reset. It's wired through to the Fan Relay and simply replicates the otter switch function of completing the circuit to earth. The switch was period Lucas but with the slightly smaller switch handle.



With regards to the wiring, the S1 3.8 Wiring Diagram points to it normally being connected to Fuse 6. That also powers the Horn Relay, Washer and Stop Lights and would normally only be active with the ignition switched on. Which fuse is yours connected to?

[peters3103]

Good question Phil but obviously the fan doesn’t switch off with ignition. It was like that when I bought it. Electrical isn’t my strong point either but I will investigate. I actually have a spare switch like yours so might save myself £23 plus post and use it as you have.

Pete

[peters3103]

With regards to wiring in a fan switch, this is my non original fan relay. It has fours wires attached. The factory relay has only three correct? The Kenlowe controller has now been removed and the two wires now go to the header tank switch.

Pete

[Philk]

In terms of the relay itself, it is a Lucas 6RA as per the parts catalogue below



I've also extracted from the 3.8 Factory Fit section quite a good photo of it's position and the wiring to/from it. If you zoom in, you will see that it has only three wires connected via the spade terminals (as per the wiring diagram).




The relays often had more connectors that were required for specific individual tasks. If both your wires to the otter switch are going to the relay then I believe that is not correct. Only the live low current feed should go to the otter switch. The other wire from the otter switch should run to an earth position on the chassis. That would then leave you with the three wires (which would be correct) - One high current output to the fan, one high current input to the fuse board and one low current wire to the otter switch.

In terms of the operation, the otter switch (when it hits the relevant temperature), will close the low current circuit to earth which, in turn, causes the relay to "switch" internally which permits the high current circuit to the fan to operate.

[peters3103]

Thanks for this Phil, much appreciated. I’ll have a close look at the wiring and see what has been done. I know there is one unused wire there too so five wires in total means two have been added. I will replace my relay with the original type too.

Pete

[mtnjag]

My coolcats header tank switch has been very reliable. I also have a bypass switch under the dash like Phill. I have a 10-20 mph drive into my house coming off a main road so keeps the eng temp down on the way into the house. As mentioned those at speed drives with quick slow down make it handy.

Indicated on my gauge, which i have not calibrated but should, my fan turns on at almost 90 and off at 80. To me about right. I have a coolcats fan now and works great. You don’t want the fan running at normal operating temp. Thats the way my old Otter header switch worked and the damn fan was on all the time!

Coolcats has Temp Strips that stick on a clean location and give you a temp you can use to calibrate, I have them just haven’t done it.

[peters3103]

Yes, I’ll give my Coolcat switch a go Layne, thanks.
Phil, looking more closely at the wiring, I have the three correct coloured wires coming from the original harness that would have gone to the original Lucas relay (the green is not currently connected to my relay).There are also two black wires going to earth on a picture frame bolt. I note in the photo you extracted from Factory Fit that these black wires are earthed at the relay fixing screw. There is an addition wire added, running from a fuse near the battery (where the control box used to be) to the fan relay. I’m now running a Dynamator so control box not required.
If I can find a C18122 6RA Lucas relay I’ll fit and connect it as per the wiring diagram and see how it goes. Looking at the fuses there are multiple green wires on the number 6 fuse. I’m not sure which is terminal 4.

Pete

[Philk]

Phil, looking more closely at the wiring, I have the three correct coloured wires coming from the original harness that would have gone to the original Lucas relay (the green is not currently connected to my relay).There are also two black wires going to earth on a picture frame bolt. I note in the photo you extracted from Factory Fit that these black wires are earthed at the relay fixing screw. There is an addition wire added, running from a fuse near the battery (where the control box used to be) to the fan relay. I’m now running a Dynamator so control box not required.
If I can find a C18122 6RA Lucas relay I’ll fit and connect it as per the wiring diagram and see how it goes. Looking at the fuses there are multiple green wires on the number 6 fuse. I’m not sure which is terminal 4.

Hi Pete

The additional fused wire you've photographed which runs to the fan relay could well be the cause of your fan running on past the ignition being switched off [I would also highlight that, in reality, that achieves nothing in terms of the engine cooling down after it is switched off given the water pump would not be circulating any water around the engine. All it will do is cool the water down in the radiator and drain the battery].

Moving forward, if you have a multimeter, I would attempt to test the continuity of each of the wires on Fuse 6 through to the wires near the fan relay - be sure to disconnect each wire from Fuse 6 prior to using the multimeter since, otherwise, you will end up with spurious results. If you can find the wire to Fuse 6 then that will be the one which will need to be connected to position C2 on the 6RA relay (incidentally, there is no reason why you cannot use your existing relay to try this out since the terminals ought to be labelled or you can look their function up on the net). The 6RA will provide you with period appearance though.

Hope this assists.

Regards

Phil

[mtnjag]

Not a wiring expert and perhaps I’m stating whats been said but sounds like you are constant hot at the fan circuit circuit rather than switching the power through the relay? But not the fault of the fused wire from the battery junction.

If you poured boiling water in the header tank when the eng is dead cold you fan would probably start without the key.

So you probably have a full time hot wire connected to the relay rather than a switched trigger wire from the dash fuse panel. Track down as Phil advises.

[mtnjag]

Or just short the otter switch, fan should not start with key off.

[Philk]

I should have said that my suggestion re tracing the wires was simply to identify what should be the correct wire that needed to be connected to position C2 on the relay. Once that is done, it would then be a case of disconnecting the permanent live feed that appears to be coming from the extra wiring present where the RB310/RB340 used to be.

[mtnjag]

I run a hot lead from the batt term junction to the relay. However it is connected to a switched relay input. Doesn’t sound like that’s the case on Pete’s car. Im using the 6RA relay, cant tell you right now what terminal its connected to.

Still thinking he has mixed wires on his factory panel and is simply running a full time hot to the relay trigger terminal on the relay instead of an ignition hot wire. Simple VOM check at the Otter and to find right wire behind dash.

I was running an adapted Camaro fan motor that pulled something like 20 amps so we took the power feed out of the factory harness. Finally switched over to the Coolcats fan which is supposed to draw something like 7 amps so all would be good with factory wires but it’s all set up and works fine so haven’t made the change back.

[peters3103]

I’ve just removed the additional “hot” wire from the relay and connected the unused green wire from the harness. The fan is now working only with ignition on. I’ll now replace my fan switch and all should be ok. I’ll still add the under dash switch and replace the relay with an original type for authenticity. Thanks for all your input chaps.

Incidentally when I opened my dash panel there’s two purple wires - one with a white stripe, that have come off the map light. If I connect them both to the lamp it’s on all the time regardless of map light switch position. The purple wire is live all the time whether switch is on or off. I’m sure it was connected and working previously. Any thoughts?

Pete

[mtnjag]

Sounds like your door is open?

Or possible the door switch is going to ground?

Same light function in my OTS anyway.

[peters3103]

I AM AN IDIOT! Yes my door was open. Completely forgot the map light is triggered by the door switch.

[mtnjag]

I love a simple solution.

Hey, we’ve all neen there!