Cooling fan wiring

[jimj]

My electric fan is wired through the ignition, neatly to the fusebox. As a result, when the engine is stopped so does the fan when it might be better if the fan ran on until the thermostat recognised the drop in temperature like most other cars do.
So, how would you neatly wire it?
Jim

[gjz30075]

Jim, I don't think most other cars have their fans run on after shutting off, otherwise we would hear all over the place in parking lots. None of my cars, '97, 02 and '11, run their fans after the ignition is shut off. I don't think there's anything to be gained by doing so.

At this point, the coolant is not circulating and the fan would be cooling the coolant in the radiator, not in the block where the thermostat resides.

Just my .02

Greg Z

[Galwaylotus]

Ditto. What's the point of cooling the radiator when the engine won't "see" any difference?

[nebogipfel]

My original Sprint back in the 70's had a fan which continued to run often for some time after I had parked.

The Sprint I was parked beside on a recent classic run did likewise.

While it's true the coolant is not circulating it is still cooling the radiator and probably as importantly the engine bay.

[jimj]

I have certainly heard no end of fans running after cars have parked, not least ours, which is why I asked the question. Clearly, it must help reduce heat soak. Does anyone have the answer?
Jim

[cliveyboy]

I think Jim mentioned the magic words "heat soak"
My thoughts are not so much for cooling the engine down (although it helps) but to keep the carbs from heating up and getting vapour lock.
If your car has been running around and not overheating then when you fire it up again the temp of the engine should not be an issue. But when stood still with no air flow or cool fuel going through the carbs then they might heat up.
Had this lots of time on other classics. But never an issue on my Sprint whose fan does not run on after engine switched off. I am currently messing around with the cooling system and might wire them up to run on after engine turned off. You obviously need to make sure the fan/s do not run for too long and drain the battery
On my Excel it had a small "plenum pump" which pulled air through the air box after the engine was switched off. This was to stop the Dellortos from heating up.

Clive

[paddy]

I also have the fan wired to continue running if needed without the ignition.

If you already have a wire going back from the fan to the fuse box, I don't understand your question about how to wire it neatly. Are you looking for an alternative source of unswitched power without having to route the wire through the bulkhead ?

If that's the question, what series is it and is it alternator or generator?

Paddy

[stugilmour]

On my Plus 2, I originally wired mine to keep running, but changed it to shut off with the ignition. I am using Clive's temp sensor and relay set-up with an after market shrouded fan. The fan would typically run for about five to ten minutes after shut-down, essentially until the sensor located in Clive's modified thermostat housing reached its lower limit, which is adjustable in conjunction with the upper limit. the running time was of course effected by ambient temperature. Didn't have a problem with either wiring configuration, so opted for it turning off.

Without going into your model specific wiring details, general thoughts on the wiring configuration change are reasonably simple. Move the fan supply from the hot in run and start fuse block to the hot at all times fuse block. These are identified as white supply / green fuse output and brown supply / purple fuse output respectively if using the Lucas wiring standards; my Plus 2 was pretty consistent with these standards, but not 100% sure on your specific car.

If you have a fan relay in your set-up, both the relay main supply and the relay trigger have to be wired to hot at all times for it to work correctly. There was a recent thread that covered the relay pin/terminal numbers pretty thoroughly if needed.

As above, I have seen moderns wired both ways. One possible reason for having the fan run on the moderns may be to ensure the AC condenser gets cooled down, but just speculating. All my moderns that run the fan on are AC equipped. My '87 BMW is actually wired to always run the fan if the AC is on, independent if the temp.

HTH

[Jeff@Jae]

A good example of preventing heat soak is the V8 Esprit and M100 Elans. The fans will run after shut down but they also have a recirculation pump for coolant circulation as the fans cool down the radiator. Not unusual in some contemporary cars but I can't see that as really needed with our classic Elans, Europas etc. Emissions controlled and electronically managed cars typically run at higher coolant temperatures and have more complex coolant flow patterns. When I drive my Elan hard in high ambient temps I do pop the bonnet after shut down for a bit to cool down the engine bay. A recirc pump and switched fan would be a nice addition to a racing car after shutdown if it was to be run after short shut down periods but in practice that doesn't happen very often in my experience..

[jimj]

It`s an S3 and I thought both the upper and lower fuse connections were only live when the ignition is on. Am I wrong? is it wrong?
Jim

[Galwaylotus]

Jim, my S3 has the twin fuse panel and both supply points are from the same (white switched) source.

[Galwaylotus]

A recirc pump and switched fan would be a nice addition to a racing car after shutdown if it was to be run after short shut down periods but in practice that doesn't happen very often in my experience..

Ahh! How does that fit in with the concept of "adding lightness"?

[jimj]

So, has anyone the answer to the original question?
Jim

[stugilmour]

So, has anyone the answer to the original question?
Jim

Sorry if my reply didn't suit your S3 details exactly Jim. If you only have two fuses hot in run & start, you would want to add a fuse that is hot at all times. This would generally be supplied with a brown wire, and use purple on fuse output for most circuits.

My Plus 2 originally had two fuses, but they were as described above. Sorry for any confusion regarding your S3. Leave it to you regarding the merits of this mod, but I tried it and saw no real need for the feature.

[jimj]

Thanks for all your replies. I`ve searched the archives without success. I fear that false assumptions regarding my auto-electrical ability have been made.
What I need is a simple explanation of where to connect the live, to which connection(s) to make to the relay, what sort of relay, and how to route the wiring neatly.
Incidentally, I`m running twin 10" fans and that`s another reason I don`t think it`s a good idea to draw that much power through the ignition switch, or does that matter?
Jim