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MG Midget and Sprite Technical - One for the electricians

Previous I had my Revotec electric cooling fan kit wired to the twin spade beneath the green wires (see image) so that it worked with the ignition i.e. the fan went off with the ignition.

But when I had this I'm sure it intermittently caused the engine to run on (some sort of back or cross feed(?)).

I spoke to the Revotec guys at the NEC before the show opened for the day a few years back to see if it might be the relay in the kit or something but they didn't really want to know (I think they were still recovering from the night before).

I also have a 123 fully electronic dissy and pre-engaged modern starter but other than these three items the electrics are pretty standard.

I decided as an experiment, which became permanent, to instead run the supply direct from the battery clamp with an in-line fuse. This of course meant that the fan cut in after the engine was switched off because of the under bonnet heat build up. This doesn't bother me usually but the fan effect is noisy and my car sits outside so if I get home late at night 5 minutes after I get in home the noisy fan starts annoying me if not the neighbours.



So is there a better way to wire it so that it goes off with the ignition?

Would connecting to the twin spade beneath the white wire be the same as the green side (ignoring the fuse)?

Image is orientated to be the same as looking at the fuse box from the front of the car (standing in front of the radiator grille).



Nigel Atkins

Connecting it to the white side of the fuse will make no difference, other than it will be unfused.

Can you post the whole of the fan wiring circuit?

It would be useful to know if you just have one power connection for both the relay switching and fan power; whether the relay is switched live or ground and whether the fan is switched live or ground.
Dave O'Neill 2

Use a ignition switched supply for the fan controller and try not to use same supply for both fan and controller (study circuit diagram in the handbook!). Have a look at the Revotech website and the diagram for their controller will explain, although they've used a common feed.
Motley 5

Nigel
You could try fitting a diode between the fuse box(green connector and your fan feed wire
This would eliminate any feedback from the fan circuit if the fan happens to be on when you turn the engine off

I suspect what is happening is that if the fan happens to be going when you turn the engine off, - while the fan is still spinning, which it will do, it will act as a generator and give you a feedback till it stops spinning------a diode should fix it

willy
William Revit

Thanks for your replies. I'm trying to keep the fan load (is that the right word) to its own wire/circuit and connections as few as possible, especially existing bullet connectors.

Which/what diode would I get, to me it'd be like looking down the washing powder/liquid aisles of a supermarket, hundreds to chose from but I've no idea which I should use. Also Revotec told me it shouldn't happen so I *shouldn't* need a diode.

As you can tell I can't go into Radio Shack or whatever it's called now and explain what I want as I can't talk jargon with a techy type.

Aren't diodes flimsy things, how do you fit them robustly and protect them from accidental damage, if the fan doesn't work it's bad news, I don't want to be constantly having to watch a tell-tale light to make sure the fan system is working, none of us do this in our more modern cars.

I previously drew below for my records (I think I got it right) and Revotec wiring to follow.

I put separated earth points for stat and motor.


Nigel Atkins

I got the image below from the Revotec website previously, it's off the Revotec fan fitting pdf (issue 2, 6/8/2014)


Nigel Atkins

I am surprised that your present system wakes up the neighbour's dog 5 minutes after you have gone to bed. Or even that the fan should suddenly come on after as much as 5 minutes after you have switched off (the engine).

Mine is wired to run on when the ignition in the off position, but only ever does so for a couple of minutes immediately after parking. It never seems to suddenly wake up again after a delay. Why would it do that?
GuyW

Re your diagram. Connection at 30 is as it should be from a fused(?)12v supply.
Pin 86 should be from a switched ignition feed (white wire?). No red between 30 and 86
Motley 5

What Motley says.

As it is wired at the moment, as you switch off the ignition you lose the 12v feed to the relay, however, if the relay was engaged and the fan is turning, the voltage being produced by the fan as it spins down, is being fed back through the ignition circuit.

If you have the relay coil (86) and controller fed by the ignition circuit and the fan power (30) fed from a non-ignition switched source, all should be well.
Dave O'Neill 2

Your Revotec controller is wired exactly the same way as on my BV8, and on the Elan I owned, with power from the green circuit. There is definitely a generator effect when the fans are windmilling. At 70 mph at night, the warning lamp I installed on my dash is glowing even though the fans are not powered. But I have never had the running-on problem on either car. The V8 has fuel injection so that probably shuts the motor down, but the Elan had carbs. I'm struggling to understand how having the fan running at key switch off can cause feedback of voltage to the car's ignition. But then I'm no electrical genius. I just follow diagrams when it comes to wiring.
Mike Howlett

I went to Radio Shack, now known as The Source for some spade connectors. Believe it or not, the electronic days are done. I was told they are not stocked any more and have to be ordered online!

They had a myriad of electronic devices such as cell phones and the like but no bits and pieces.

Found what I needed in Crappy Tire. Actually, it is called Canadian Tire but no one calls it that. (lol)

Clare
Clare Ravenwood

" I'm struggling to understand how having the fan running at key switch off can cause feedback of voltage to the car's ignition"

At switch off, the relay will remain energised as the spinning fan will be generating a voltage which will also power anything on the green and white circuits, including the ignition coil.
Dave O'Neill 2

Yep, the fan will make the engine run-on (Peter Baldwin told me that years ago).

Currently my car's fan is wired ignition live through a toggle switch but I'm about to wire it to come on via a thermostatic switch fitted to the radiator - through a relay - with the toggle switch as a manual override. Some relays have a diode built into them.
Daniel Stapleton

Indeed, some relays do have a diode built in, but that is for arc suppression. It won't help with this problem.
Dave O'Neill 2

Hi All,
thanks for all your replies.

Guy,
the delay varies, sometimes it’s a matter of seconds other times minutes, 5 minutes was more a figure of speech, it does sometimes run on for quite a time and it certainly sounds that way late at night. I have an uprated fan so it’s even noisier than when I had a standard fan, luckily none of the near neighbours has dogs.

Motley, Dave,
the relay has a small link wire “from the factory”, I think I have the terminal numbers correct, note the Revotec diagram shows a link on the 12v red wire.

Mike,
mine was wired as per Revotec instructions it was just a case of the car was getting the possible run-on from it but it only happened a few times intermittently, the direct to battery connection was supposed to be a short term test but became handy in summer use and got forgotten about except when late night parking.

Clare,
I don’t think we’ve had Radio Shack in our town for decades but I can’t remember the name of the electronics type shop, if I put Matalan UKers will know who I mean as I still can’t think of the name. (ETA: it’s Maplin)

Daniel,
for a street car I can’t see the point of an override switch (or tell-tale light) as it’s like having a dog and barking yourself and we don’t have a tell-tail light to say our brake lights are working and that’s more important than a hot engine, but as always each to their own.


Thanks All,
based on your replies I’m going to wire off the spare ‘white’ spade with in-line fuse and report back if and when it runs on.
Cheers.

Nigel Atkins

Nigel,
Although I post in light hearted terms (waking the neighbour's dog) my interest is genuine. One would expect the coolant to be cooling down after switching off.

I can only surmise that the heat in the casting of head and block is being dissipated in your nicely cleaned system into the, now unpumped and non circulating water giving a local increase in water temperature. Perhaps the delay is as this heated water gradually rises through the cylinder jacket and eventually concentrates the heat in the area where your thermostat is located? Are you using a thermostat in the radiator, top hose or cylinder head?
GuyW

Sorry Guy I totally missed your question, I had the page on half screen.

The thermostat is in the top hose.

I assume it's general under bonnet heat build up, umpumped coolant, oil still and dropping down, heat off the stainless steel manifold - but the bonnet has no insulation.

I wonder about the rad, I'm changing it anyway this year after getting a pinhole leak but it's been cleaned at least once and thoroughly flushed and back flushed two or three times at least.

Unfortunately the 4-Life never gets anywhere near its 10 year life, the oil is less seven months old and a good quality, proper synthetic, for high temperatures. The fan is uprated so should run for shorter periods.


Nigel Atkins

Guy, have you never noticed your (capillary) temperature gauge rise after switching off the engine?

Nigel, that link is helping to cause your problem. If you remove the link, connect terminal 86 to the ignition-switched circuit - either green or, white - take a separate (fused) feed from from the brown circuit, either from the fuse box or the solenoid, to terminal 30. Job done.
Dave O'Neill 2

Nigel
Both the wiring diags. that you have shown ,yours and Revotech's are the same, so you have it wired as per instructions- but it's wrong
Pins 30 and 86 should not be linked---this is the fault
What you need to do is--
Have a fused constant 12v supply to pin 30 and the controller as per the diaghram but have a seperate wire from the ignition circuit to pin 86 with no connection between 86-30

Same as Motley suggested earlier

There won't be a need for a diode wired like this
willy
William Revit

Dave, yes indeed it does, but the sender is in the head where the excess heat is. That's why l asked Nigel where his thermostat was.

What l was really after was why the long (5 minute) delay before Nigel's fan starts up. That length of time seems surprising to me so long after the source of the heat has been turned off.

Many modern cars have fans that run on if they are hot. My Sprite fan doesn't often come on but if it is running when the engine is switched off it will run on for up to a couple of minutes sometimes. I have never known it to suddenly wake up 5 minutes later though.
GuyW

Guy, Nigel corrected that bit:
"the delay varies, sometimes it’s a matter of seconds other times minutes, 5 minutes was more a figure of speech"
davidsmith

yes he did, though I still understood that there is a delay before the fan starts up, not simply that it continues to run. It implies a movement of heated water up through the system to the location of the sensor. That is all I was getting at, not that there is anything wrong.
GuyW

Willy, Dave, Motley,
I'll email Revotec to see check the link wire, I was originally sent the wrong fan which took me a bit to check and get them to accept so perhaps I have the wrong relay.
Nigel Atkins

Guy,
next time it happens (and I remember) I'll make a note of the timings but I'm not using the car much at the moment and for about the next couple of months I'll probably be using it even less.

Even though I try to keep the oil and coolant systems clean I've never had the engine apart and cleaned, the engine, radiator, cross pipe and heater matrix were in the car when I bought it.

When I bought the car the engine was supposed to have been reconditioned with only 50 miles on it. I gave it a graduated 2k-mile run-in with a couple of oil & filter changes and changed the coolant (to 4-Life).

I can't remember at that coolant change noticing much crud but when I changed the coolant again 11 months and 5k-miles later because of HGF (I also changed the oil & filter) I was surprised at the amount of crud that came out of the coolant drain hole on the engine block. Whether the extra heat had loosened the coolant crud I don't know or whether I forgot or didn't check the drain hole previously I can't remember.

Considering the engine by that time had only done 7k-miles since being reconditioned, and to me the engine felt like the work had been done, there seemed a lot of crud but I don't know what and how much work is done to clean the engine waterways when reconditioned.

Water side I've replaced (sometimes more than once) thermostat, stat housing, all hoses, top pipe, pump, heater tap, gauge and coolant.

As put I've cleaned and thoroughly flushed and back flushed the radiator and heater matrix but still don't know how crudded up they might be internally so I wonder about the rad not being fully efficient.

Nigel Atkins

Nigel, as l said, l wasn't ever suggesting anything wrong. If anything, maybe your well cleaned system is allowing free thermal movement that others may not. Or perhaps it is a function of using a water wetter product?

To my way of thinking though, if your thermostat is reacting to an excessive build up of heat then it would be better that this was dissipated by having a fan that does run for a few minutes, rather than altering the electrics to prevent it from working.
GuyW

I've come in a bit late to this thread so it may have been said before, but I thought it was normal for the engine temperature to rise after the engine is switched off because the excess heat stored in the block etc is no longer dissipated by the circulating and fan cooled coolant.

It follows that with an electric fan controlled only by a thermostat, the fan will continue running, or cut in some time after switching off when the coolant temperature reaches the temperature setting on the thermostat sensor. And with no water pump running, it will take some time for the heat to reach the sensor by convection.

Is this not what happens in a modern?
Peter Blockley

Yes Peter, that's pretty much as I said. My only surprise was that the delay was as much as the 5 minutes that Nigel mentioned initially. But I was taking him too literally at this. ;-)
GuyW

Hi Guy,
it's not you but me suggesting there might be something wrong. I was supplying more background info for you and as a bit of a sounding board for me.

Out of interest what and how much work is done to clean the engine waterways when reconditioned?

All being well I'll change the rad later in the year anyway, I know none of the nuts & bolts will be be seized up at least.

ETA: Peter, I've never know the fan to operate on my wife's modern diesel but the cooling system are more efficient and engines more (electronically) on moderns.

Nigel Atkins

The offending link.


Nigel Atkins

The override switch is so I can flick the fan on when I see a traffic queue ahead and don't see a need to wait for the fan temp switch to do its job + its there for when the fan temp switch fails!
Daniel Stapleton

"Out of interest what and how much work is done to clean the engine waterways when reconditioned?"

On a race engine it would be stripped down to a bare block, core plugs and the brass oilway plugs removed. Immersed in a hot caustic tank perhaps overnight, then flushed with water. The oilways should be rodded through then blown out with an airline. At a minimum.

But on a road-spec Ivor Searle-type recon, who knows?
davidsmith

Daniel,
what about if the switch fails!?!

Nothing wrong with belt, brackets and a bit of chewing gum excepts it gets a sticky. ;)

As always each to there own but to me as you have it you have a dog but barking yourself encouraging your dog to bark.

You could have a two stage switching fan or two individual fans with individual switches or one double stage switch with two fans, Andy Frakenfrog would do the development work on these. :)
Nigel Atkins

That's the thing Dave I suspect the waterways might sometimes be pretty much ignored.

Things need to be more thorough for competitive sports, back in the late 70s and early '80s I used to spectate at Santa Pod Drag races and the big pro engines were stripped down just about after every race.
Nigel Atkins

I sent an email with my drawing and photo to Revotec to check the supplied relay should have a link wire between connectors 86 & 30, this their reply -

"Hi Nigel

Yes, the link wire is correct, as it should be.

Kind regards

****"
Nigel Atkins

Guy,
another thought, aspect, I don't know if you know but the stat is adjustable so the higher it's set the longer the delay. At one time I had the stat set higher as an experiment to the car's running, like when I had the 88c water stat (went back to 82c).

Now I have the fan set to kick in a bit after 'N' on the gauge which I feel more settled with but of course that leaves less margin for heat build up after engine switch off.
Nigel Atkins

Nigel

The link wire will be fine if you are using a permanently live source, but the fact that you have it connected to an ignition-switched source is causing your engine to run on.

Your two choices are either move the feed to a non-switched source, or have two separate feeds for the coil and the load, as previously suggested.

The former is easier, but that means you will wake the neighbours.
Dave O'Neill 2

Hi Dave,
you're highlighting a problem with having a relay - far too many and too much thick wires so that there can be very short lengths of thin wires to small switches - but I'm not blaming you for this. :)

For quite a while now it's been wired straight off the battery live post with an in-line fuse.

What I was trying to explain to the Revotec guys at the NEC was that this kit is designed for the midget so should work without causing run-on (if it was the cause) if wired to their instructions, they said they'd never heard of the problem. So perhaps the run-on wasn't caused by the relay wiring, perhaps it was the fuel used at the time, it was only a couple of intermittent times.

I had just made my mind up to run from the spare white wire spade on the ignition switch with the in-line fuse but now I think I'll now wait until the hot weather with new rad fitted and see the delays and length of run-on then.

From their leaflet -
"Connect the RED wire to a fused 12v supply. It is recommended that the feed is from an ignition
controlled supply such that the controller will not operate when the engine is switched off. If the feed is
connected to an un-switched supply the controller will continue to operate and may run the fan after the
engine is switched off, if the temperature rises above the setting."

I'll report back in the summer if/when I remember and get aroundtuit, cheers.


Nigel Atkins

Nigel
A few on here have tried to guide you as to how to hook up the fan relay---------
Hope you don't mind, I have taken the liberty of modifying your wiring diagram to one that
Will work properly---
Won't make your engine run on--

Run it by Revotech if you want-but this is the answer to your problem

It involves isolating the 86 circuit from the 30 circuit
by disconnecting that linkwire from the 86 pin
For this to work properly pin 30 needs to be on a 12v feed NOT ign.
And pin 86 needs to be fed seperately from 12v ign.

willy

Interesting that Revotech have gone for a transistor type controller needing a power source instead of a more simple sink to earth type sensor---sign of the times I guess




William Revit

Nigel,
Why not move your sensor to the bottom hose.
I had similar issues with heat soak causing the elec fan to run on for quite some time.
Moving the sensor to the bottom hose cured it as the cooler water always goes to the bottom.

When running, the temp of the engine is governed by the thermostat, controlling the fan by the bottom hose controls the temp of the water going into the engine.

I was sceptical at first, but my engine and cooling system runs fine.....
I got this advice from the Datsun1200 site .
Andy Phillips (frankenfrog)

Hi Willey,
thank you for the drawing, I do appreciate your time and advice and the advice of others. I did understand what you meant but you wouldn't know that from the way I write.

You might have missed that I've never actually confirmed that the fan did cause run on because I didn't put it back to an ignition source and it was just a couple of, intermittent, times.

I'm pretty sure Revotec would say I could wire as you've put, the fan is out of warranty anyway, what I don't like is yet another wire (and connections), pity the switch can't take the full load (I know it can't) and do away with the relay.

I'd have to use individual insulated spade connectors instead of the existing female connecting block as I don't have a proper uninsulated crimper and the quality of uninsulted spade connectors I've seen and previously used have been very poor. There's not direct live supply on that side of the engine bay I can think of so it'd be another long wire run from the battery or solenoid.

Sorry I might be a hopeless case as far as this goes as the extra work on top of all the other annoying jobs on the to do list will need a roundtuit, I already spend far too much time doing things on the car compared to the far to little time driving the car. Of course if I don't do it I might feel differently next winter.
Nigel Atkins

Hi Andy,
a few years ago my mate with a classic Rover told me about the top/bottom hose debate on that car's forum and he decided on top whereas I thought you could do either and just adjust the switch setting as required.

On the 1275 x-flow there are three bottom 'hoses', two rubber (silicon in my case) and a metal cross pipe because the rad bottom outlet is on the other side to the vertical flow rad. The rubber hose that connects the rad to the cross pipe is very short and the hose from the cross pipe to pump is curved so would be difficult to get a good fitting of the switch insert.
Nigel Atkins

Since the purpose of the electric fan is to come on only when required, it seems odd to try and stop it from operating in response to the highest temperatures in the system, which will be at the top, or top hose. And moderns are configured so that the fan will run after the engine has been switched off, presumably with good reason.

Apart from not upsetting the neighbours with the roar of your fan late at night - (as if they hadn't already been woken by the reving engine and slamming doors as you return from your foray to the late=night chippy) I don't see the problem of a fan that wakes itself up and runs for a couple of minutes. It seems to be fussing over nothing.

Actually, there is a good practical reason which has caught me out once or twice, though never on the Sprite. It can give one quite a start when reaching into the engine compartment for some reason or other, when the fan suddenly comes to life.
GuyW

Hi Guy,
you must have switched threads.

I'm more doing a feasibility study at the moment. If you heard the fan you'd know what I mean, when I put late at night it could also be (although very rarely now) the hours after midnight and we live in very small semi-detached bungalows that are quite close to each other and it's usually very quiet here at night.

It's more that it annoys me as the car is parked only feet away from the living room and not many more feet away from the back (and only) bedroom.

In summer the fan carrying on is handy but the engine then cools down quite quickly soon(-ish?) getting to 'C' even in summer but in winter the extra cooling isn't needed.

With moderns the whole cooling is more efficient, on my wife's car I've never heard the fan cut in in 7 years.

Having put all that now winter has passed it's not urgent and I could try plugging back to the ignition wiring to see if it really does cause the engine to run on (the original reason of the thread).

At least I don't have to worry about exhaust noise anymore as some of the recent nieghbours (moved in in the last decade) have much noisier exhausts.
Nigel Atkins

Don't think I have switched threads. It was about the fan control, and whether it continues, or starts to run after you have switched off and gone indoors?

But, - "cause the engine to run on". I must confess I had missed this aspect entirely! In my experience running on is often caused by either a weak fuel mixture, or use of the wrong spark plug, or maybe a build up of carbon if its a higher mileage engine.

But re-reading, at least excerpts from the thread, are you saying that the Revotec controller is providing a feedback into the ignition circuit and so continuing to energise the coil and keep the engine running? I misunderstood that!
GuyW

Hi Guy,
the switching threads comment was because your previous post on this thread was emailed to me as a first reply on my thread for Andy, so I thought you’d posted on that thread realised your mistake, deleted it and reposted here, I’ve no longer got that email to check, must be a site anomaly.

Yes I thought about the usual reasons for the engine run-on but IIRC it was only twice and at different times, perhaps it was funny fuel combined with fuel vaporisation from a hot runs on a hot days and then left to idle at parking but I can’t remember the details now. All the runs before and after didn’t cause it, same plugs, same engine, don’t know about fuel – there was something that put the relay into my mind as a possibility which is why I asked at the show.

I don’t know what from the fan is the cause or even if it was actually the cause, I wanted to check possibilities of wiring and possibly see if it happens again to confirm but that’s never easy with something so infrequent and intermittent.

If I can avoid it I don’t want to have more wires, by choice I’d have a system without the relay, it’s just more wires and connections with an extra component for no benefit in this case other than the need because of the small fan controller.

6 wires instead of two and that’s progress. :)
Nigel Atkins

Guy

It's not so much the Revotec controller providing the feedback.

With the 12v feed taken from the ignition-switched side, if the fan happens to be on when the engine is turned off, the spinning fan will generate a voltage which will keep the relay energised and will also feed back to the coil, etc.

It will not keep the engine running indefinitely, only until the fan stops spinning, or loses sufficient speed that the relay drops out.

Even without the relay being there, you would get the same effect.

If the fan isn't on when the engine is turned off, there will be no feedback and no run-on.
Dave O'Neill 2

Thanks Dave, that's the clearest explanation yet!

I must admit, despite the thread heading I wasn't really focusing on the electrics, knowing that others here are far better informed to advise Nigel on that. I have been wondering why a fan that continues to dissipate excess heat after the car has stopped is considered a problem. I would take it is a good thing!
GuyW

Curiously, when I arrived home yesterday, the fan on my modern was running after I switched off. I hadn't noticed it before.
Dave O'Neill 2

Interesting Dave I only noticed the engine run-on twice but I'd imagine the fan would have been running when I switched off the engine a number of times more.

If it does it (regardless of relay) and the engine only ran-on for a very short time on those two occasion is there any real harm?
Nigel Atkins

No harm, I just thought you wanted to stop it from running on.
Dave O'Neill 2

Hi Dave yes I do but I now realise it's my terminology that's causing problems too.

I want to stop the engine running on after I switch off the engine - but it might not be the fan causing this as it's only happened twice (when wired to ignition suplied).

And I want to stop the fan running on after I've switched the engine off by going back to wiring supplied by ignition.

But none of these are a top priority just niceties for when I don't want to do other work on the car or if it involves hoses to do when I fit a new rad.
Nigel Atkins

Just finished testing the new thermostatic switch and it appears to be faulty = brand new out of the box. Completely faulty in that it doesn't switch the fan on at all and double checking by putting in a cup of boiling water and re-fitting to the wiring. I guess I now need to remove it again and use a multi-meter while boiling it up in a cup.

And that's the reason I have a manual fan override switch.
st

Presumably your testing before you fit it to the car so still don't need an override switch?

(No, I didn't test mine off the car before fitting)

If it's the Revotec, it doesn't have markings so could you have it set for the fan to cut in at 120C instead of 70c for setting up by having it installed the other way round?

I'm not trying to be funny btw, just asking.
Nigel Atkins

This thread was discussed between 02/03/2017 and 11/03/2017

MG Midget and Sprite Technical index

This thread is from the archive. The Live MG Midget and Sprite Technical BBS is active now.