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MG Midget and Sprite Technical - Electric fan sender

I'm going to fit an electric fan to the Sprite. I have one of those adjustable temperature switches where the probe is put in the top hose. I was thinking of fitting this in the head, in the plug below the thermostat housing. Has anyone done this or would it be better to fit the temperature gauge in the head and put the fan sender in the radiator. What water temperature should the fan ideally kick in? I was thinking of getting a fixed range probe instead.
Thanks Andy
Andy Potter

Gday Andy How did you plan to fit the probe to the head?
this sounds like hard work. Putting it in the top hose is where it was designed to be, the only problem being is how to seal the capillary tube satisfactorily, from memory this is done with a little rubber saddle with a cut out for the tube which fits on top of the inlet tube to the radiator with the hose going over it and the entire assembly secured by a hose clip. It works but you have to stretch the hose beyond its design limits to make it fit and then hope it doesn't leak.
I don't like this system and I solder a brass fitting to the top radiator tank to take the sender/switch. A bit of a faff but far more elegant and reliable. see pic
This is on a 1500 but should give some idea as to how to proceed.

I'd leave the temp sender exactly where the factory put it.
HTH
Cheers
Rod


R W Bowers

My concern was getting leaks around the probe as the hose is no longer round as you mention. I have seen the tapped hole in the head under the thermostat housing which is currently plugged used for a temperature gauge probe on other A series cars, I think a Morris Minor or A35. If I fit the temperature gauge as in the photo I can put the fan probe in the radiator.


Andy Potter

Rod's image of the layout of his heat sensor also shows what appears to be a modification to the upper radiator shroud with some metal grille.
What effect does this have Rod?

Dave
D MATTHEWS

I think that Rod has his electric fan under there.

Andy, the 1275 Spridgets had the temperature sender in the head, as did Minis, 1100s, Metros, marinas, etc.

Morris Minors and A35s didn't have the luxury of a temperature gauge as standard.
Dave O'Neill 2

Yes lads the mesh lets in more air (I hope) and the fan is indeed under there, I had to cut the shroud to fit the 12 inch fan so took the opportunity to provide more air flow capacity. It seems to work well, but I think we all realise that the problem is getting the air out from the engine bay, hence the spirited ongoing debate on where to fit vents/louvres etc.
cheers
Rod
R W Bowers

Dave
So if I get the adapter used on 1275 for cross flow rads I should be able to plumb my capillary gauge straight in?
Andy Potter

Another question, sorry,. Is the rad a worse place to have the sender for the fa than the top hose? I have an adjustable switch so can compensate a bit for its position. Anyone know the water temp when it should switch, how do i gauge when the fan should start? Sorry more than one question. :)
Andy Potter

An alternative option
I have the fan wired, without sensor, to an on / off switch on the dashboard so that I operate the fan as & when I want.
Alan
Alan Anstead

Andy

Yes to the adapter.

I would have thought the rad would be better than the top hose. I think the top hose is only used as it's an easy aftermarket fit and not many cars have a spare port in the rad.

Setting will be a bit of trial and error, I would think. Run the car and watch the temperature gauge, then adjust the 'stat so it controls around 'N' or about 190º, depending on the type of gauge that you have.
Dave O'Neill 2

Rod,
Are you sure of the direction of air flow in your extra mesh grill in the shroud?

On the earliest frogeyes they had no shroud at all between the grill opening and the radiator. It was quickly confirmed that at speed (i.e. over about 20mph!) the air being forced in through the grill spilled around the sides of the radiator rather than going through the core and it was far less efficient. An air box was added to the underside of the bonnet to create a duct to the radiator. The ram effect of forward motion then forces air through the rad core and this is the form of construction on all of the later cars.

That's the theory anyway so it would be interesting to know if your shroud vent is allowing air to escape, or providing an extra route for the fan to draw air in by. Of course the spilled air may then have greater influence on the under bonnet temperature which may compensate to some extent.
GuyW

Guy I naturally assumed that air flow would be through the front of the car as there are two ways on a rubber nose for the air to get in, thru the hole in the bumper and thru the original holes under it if you know what I mean. Very difficult to test your theory. In practice the fan draws air in at any speed and effective , rapid cooling is achieved. IMHO, high ambient temperature, a small radiator and a cramped engine bay are the main problems.
Cheers
Rod
R W Bowers

Yes Rod, clearly air enters through those two holes , in and beneath the bumper but from there on in the air is forced through the duct and radiator shroud and then through the radiator core. There is no escape route, as it were. That's the original design anyway. As I said, the earliest cars didn't have this ducted route and air spilled around the sides of the rad. reducing its efficiency.

Its not my theory though. It is how the design was developed. I am not suggesting yours doesn't work - I am in no position to do that and anyway your experience suggests that it does. But it is an interesting deviation from the original design.

My suspicion is that once you are at speed more air is entering through the bumper and front valance than can go through the restrictions of the rad, and this air is being forced OUT of your new vent where it then circulates through the engine bay thereby improving cooling in the underbonnet area. At lower speeds when the forced air intake is reduced, your new vent may be allowing more air to be drawn IN by the fan so you get the best of both! ;-)
GuyW

Andy,
I'm with Dave, mine is set to cut in just around when the needle gets to 'N'.

As I've just put on Mike's thread - "You want to set the dial so that the fan cuts in and out after the water thermostat is open. You should be able to see when the water stat opens by watching the temp gauge when the engine is first warmed up as there will be a sudden (slight) drop on the needle after the steady rise.".

Of course having the whole cooling/heating system thoroughly clean and all components in good condition really helps otherwise the fan might have a tough job to do.
Nigel Atkins

;-) tongue in cheek and a big smile Nigel.

Your thermostat is still in there all through the hot weather last year and only once did I worry in standing traffic.
Its the big flush out that's been the good thing.
Dave Squire

Dave,
I've got 82c (water) stat and I still don't like to see the dial above 'N'. I guess I've got so used to mine running low on the temp gauge that when it gets to the 'N' I worry (or is my old age?).

Even with the 82c the needle got well passed the 'N' on the Welsh hills this year, mainly because I couldn't attack them with my usual higher speed run up as my verbal handbrake seems to active sooner and more often now and I've no way of re-calibrating it.
Nigel Atkins

Hi Guy and lads, no offence taken mate, how on earth could we check this anyway. My premise was simple, that more holes at the front must let in more air, your suggestion is intriguing however. Anyway I'm still grounded over 30c if the engine doesn't overheat the driver and passenger do - solution, drive the air conditioned 2500S (in 1978 Triumph OZ produced a few factory aircon cars, to my knowledge they may not have appeared anywhere else, I am very lucky to have one of these)
Originally I used an 85c switch but the fan ran pretty much all the time, I couldn't get an 87c so I have an 92C now and find myself manually flicking the fan on as required. Whatever, it's not ideal, but we expect to manually control pretty much everything on a classis car - part of the fun????
The temperature sender to the gauge on a 1500 is at the thermostat housing, my digital gauge routinely hits 95c here (pulled up at the lights etc), this is when I manually switch the fan on. The temperature difference between the switch in the rad is therefore quite dramatic because the fan hasn't switched on, as I said I need an 87c switch.

Cheers
Rod
R W Bowers

Thanks for all your comments.
I'm going for gauge in the head and fan in the radiator, seems much better than dangling the sensor in thr top hose. I am also fitting a manual override and light just in case...
Cheers Andy
Andy Potter

Just a point about when the fan switches in:

When I was setting mine up the research that I read said that a free-running, freewheeling fan is less of a restriction to the natural airflow through the rad when at speed than is an electrically driven fan, where the speed is controlled by the motor. If your fan switches on at too low a temperature, then at high and even moderate road speeds it will actually reduce the efficiency of the radiator.

Its well known that cars, at least in cooler climates like the UK, are more prone to overheating when in slow moving stop start traffic, generally below about 20mph. This is when you are likely to need the fan and it may need to come on. But it shouldn't be coming on when the car is at normal running temperature as this will restrict air flow when at speed. It needs to be set so the fan comes on when it is needed to correct a developing problem, as the needle moves towards the upper end of the "Normal" part of the temperature range. Remember that a cold running engine is not a good thing as it will be less efficient, less powerful and will wear much more rapidly.
GuyW

Cheers Guy, sound advice. I use my car for my daily commute hence fitting the electric fan for traffic. Any idea how close the fan cowl should be to the radiator fins? The kit has those cable tie affairs that pull through the fins to clamp the fan to the radiator core. Have to say I'm not keen on this and was going to make some brakes to attach it to the radiator cowl sides.


Andy Potter

As Alan says, just switch it manually. On a Spridget it's not as though it is going to be called for all that often and the temp and pressure gauge is the second-most looked at thing after the road.
Graeme Williams

Does that inlet to the rad not act as a diverging duct? Dropping the pressure therefore temp and speed of the air to allow better transfer of heat from the rad to the air??

So cutting the diverging bit will stop all that.
Karl Bielby

Sorry folks late to the party. I fitted a Marina thermostat housing and switch, but the switch kept failing. I had to fit a relay and it has not failed since - 10 years so far. My fan is the type that is tied through the rad core and that is perfectly fine. The fan is thin and light so there is minimum stress. Far less faff than making brackets which I tried several times.

Interesting comments about bonnet ducting. I have never seen a fibreglass bonnet with ducting and in my experience with both types there was no difference in temperature.

Les
L B Rose

Another thought. If you use a thermostatic switch make sure it's wired through the ignition. I had a battery totally flattened by a failed fan relay.
L B Rose

In my experience original Williams & Pritchard bonnets had ducting built in, Lenham may well have done too.




David Smith

Original Ashley bonnets also had radiator ducts, although I had to cut a slot in mine for the oil cooler.


Dave O'Neill 2

Does anyone know for sure what thread is in the radiator for the temperature gauge sender? I thought it was 3/8" bspp but having tried a known fitting it is slightly different, perhaps 3/8" npt, although that would be tapered. Thanks.
Andy Potter

i think you can get them m14 and m22 the bosses are available in both sizes i used the m22 i think they are easy to get hold of.Easy to solder in radiator.

http://www.carbuildersolutions.com/uk/cooling-fans


mark heyworth

Sorry for the delay responding.
Mark I want to use the existing boss that Smiths gauge sender screws into, I think this may be National pipe straight as this is 1 TPI different to BSP. Could anyone confirm? thanks.
Andy Potter

This thread was discussed between 28/09/2016 and 28/10/2016

MG Midget and Sprite Technical index

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