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MG Midget and Sprite Technical - Heater output

Morning all,
Driving around yesterday with the top down I realised that not only was my thermostat causing the engine to run too cool (I am off to get an 88 degree one at lunch time) and hence the heater was not very hot but the fan was not blowing a great deal of air either. I had cleaned the heater element inside and out and replaced all the foam in the heater box. When putting it all back together I did notice that whatever way round I connected the heater to the loom it ran in the same direction. Is this normal? How do I know which way to connect it? It didn't seem to run faster one way or the other.
I recall on my last midget (10 years ago) the blower was quite powerful and the heater very warm.
What can be done to get it to work better? Are there any upgrades available?
It is a 1275 MK3 if that makes a difference.

Thanks
Dave
D Brown

Are you getting water flowing through it? Try feeling the heater hoses and see if they are getting hot.
Dave O'Neill 2

the fan and the loom should both have a black, and a green/yellow wire. Yours might be very dirty, making it difficult to see those colors. I can't remember if this kind of fan will spin differently if the wires are swapped, but it would be super easy for you to find out (swap them).

Is your fan spinning fast enough? They are, unfortunately, not built for ease of maintenance, and if the bushings have dried out the fan might be turning slow. If you can press off the squirrel cage you can carefully dismantle the motor and oil the bushings at each end (and clean up the shaft, and check the brushes and armature). This might restore it to its original output, if yours is slow.


Norm
Norm Kerr

Except when you are going quite slowly, the fan makes little difference. The most effective heating is when at a reasonable road speed (>45mph) and with the air control partially closed to slow the incoming air so that it warms sufficiently. If it is too wide open you just get a blast of cool air as the matrix cannot keep up!
Guy Oneandahalf Sprites

Dave,
I am getting hot (well luke warm, as the thermostat is keeping the engine at about 70c) water through it. I am not getting much air.
Norm,
I did try it. There didn't seem to be any difference. I will look into stripping the motor and giving it a lube - not a job to look forward to because as you say they are not build for ease of maintenance and I could easily break things when dismantling.

Thanks

Dave
D Brown

MGOC used to sell an uprated heater motor for MGBs. If yours is a late Mk3 with integral blower, it may be the same.

Might be worth a call. Or maybe Brown & Gammons may do something similar?
Dave O'Neill 2

If the refurbished original fan doesn't deliver the air flow you want then there is an upgrade to a GM blower that works well. It does require some modification to the heater housing though so is not reversable. I made the change on my Midget and am pleased with the result, get a three speed motor if you choose to wire in the correct switch. The installation is similar to this one shown on a MGB heater. http://www.mgexperience.net/phorum/read.php?1,519704 For my MKIII Midget I mounted the resistor pack on the opposite side to maintain room for the battery in the rear. I also had to move the housing to the side a bit for extra clearance for the blower motor and the battery, just drilled new holes in the tray and used sheet metal screws to mount the heater there.
Bill Young

Yeap you can get an uprated fan and motor but I didn't notice much different to the ones that was fitted before but that (previous) motor and fan did seem to work well

Dave are you sure you cleaned the heater matrix thouroghly that is, foward flush, back flush, shake up whilst flushing both ways, put a clean thro' and do all again

I ask as I cleaned my heater matrix and despite the engine water temp being very low the heater is still warm

I find only opening one flap on the driver's or passenger's foot well (depending on how warm you want your legs) is the best way to heat the cabin, switching on the fan seem to cool things rather than distrubuting the heat

I only use the fan to clear the windscreen (the footwell flaps would both be closed to help this)

And my cold air flap is always fully open as I normally get too warm in my car
Nigel Atkins

Er, you have got the heater tap (under the bonnet) turned full on (bar a half turn)? – yes of course you have

I had to nip out this afternoon, not far unfortunately, a 6 mile round trip I couldn’t avoid

So my mental notes -

I drove off with the heater set to windscreen (both footwell flaps closed and fresh air flap fully open) and blower on, this misted up the windscreen so I wound down driver’s window (Spridget air-con)

After about a mile and a half of easy town driving I remembered what I was supposed to be doing, I wound the window up and checked the air coming out of the driver’s side demister strip and it was hot, water temp was just away from cold (about 140 F)

Then I opened footwell flap on driver’s side, hot air but more noticeable with the blower turned off

I then tried half closing the fresh air flap and turning the blower on and then off, no real difference, with the fresh air flap fully closed and the blower on was the same as fresh air flap fully closed and blower off both seemed to stop the hot air getting through properly

My car has the aftermarket fully concertina type of fresh air ducting sitting close to the front grille aperture

My conclusions, with my car, driver’s side only
– the blower fan is only of use when not going above about 15-20 mph,
– the fresh air flap needs to be at least half it not fully open (it’s only supposed to be closed to stop exhaust fumes when stationary in traffic)
– opening both footwell flaps with warm the cabin generally
– opening just the driver’s footwell flap is best for driver only
– it’s quicker for me to find these things out than it is for me type the results
Nigel Atkins

I thought you could only turn the blower on with the flap in the fully open position - knob pushed in?!
Dave O'Neill 2

I believe that the main problem with low speed air flow from the stock later model heater is the width of the blower fan in relation to the case. At low speeds you don't have any "ram" effect in the heater inlet duct to pressurize the heater case so the fan can just spin inside and because the fan is so narrow, about half the width of the case, air just loops around from the outside of the wheel back into the inlet and doesn't go through the higher resistance of the heater matrix. The GM fan is almost exactly as wide as the case so there's little or no room for wrap around air flow and it really is noticable. You could probably improve the output of the stock blower if you added a tube to the inlet side that would fit into the ID of the blower wheel and prevent most of the wrap around flow.
Bill Young

Nigel,
I agree exactly with your results, except for the fact that the motor cannot be operated unless the air control flap is fully open (knob pushed in and turned to the right) As I said earlier, the fan is only of use at low speeds. Anything more and you are better relying on the ram effect and controlling the temperature by adjusting how wide open the air flap is. If it is too far closed, then my legs get scorched!
Guy Oneandahalf Sprites

The whole airway should be clean and open. It was not the case in my sprite: See photo

Flip



Flip Brühl 948 frog 59

This is how I add moor heath

Flip



Flip Brühl 948 frog 59

Aha, a washing line!
Dave O'Neill 2

Flip,

My 1962 Volvo 544 had a retractable screen that worked from the below the radiator with a chain that threaded through the engine bay in a tube to a ring located on the facia (dash). You could lock-in what level blockage you needed depenent on abient temperature, and it retracted automaticly.

Larry C.
Larry C '69 Midget

>>except for the fact that the motor cannot be operated unless the air control flap is fully open (knob pushed in and turned to the right)<< sorry Guy I forgot to mention like many Sprigets the original switch was broken and a new seperate switch was installed before I got the car

oh, and my motor went the other way by reversing the conections, I think, if I remember correctly
Nigel Atkins

Nigel - ah, that makes sense! Yours is actually a better arrangement.
The problem with the linked electric switch and flap arrangement is that you cannot control the air flow to the fan. Too large a volume of cold air being drawn in with the flap fully open and the air doesn't get heated enough. Sort of counter-intuitive as the natural thing is to think that the fan needs to blow more air to heat better. It is actually the reverse! Unless you can contrive a larger-surfaced heater core, in cold weather there is little point in trying to upgrade the fan.

Guy
Guy Oneandahalf Sprites

MGOC list the following up rated heater matrix as suitable for early 1275 cars:

Heater Matrix - High Efficiency ARO1994HE

HTH
Doug Plumb

the seperate switch is wasted on me as I keep the fresh air flap fully open as that's best for heat on mine, I get plenty of heat with it fully open

better fan and motor might help in summer when the heater tap is turned off, I think the design of the uprated actual fan is supposed to be better(?)
Nigel Atkins

I am with Nigel on this one.

In all the years I've owned my Midget, and driven it in freezing cold (20F, frequently, what is that, about -8 to -10C?), I have always gotten all the heat I could possibly want from the heater, with the vent flap wide open. My feet are always roasting (though, I do keep the passenger "stove door" closed to help). I just need a warm hat and gloves for the wind.

This is with a stock heater matrix, 1275 with crossflow radiator and 180F thermostat. Everything was flushed, cleaned and pressure tested by my local radiator guy when I bought the car, and the packing foam renewed. Oh, I just remembered that I do put a cover over the radiator intake (like Flip) when it is that cold, but only when it gets well below 30 or 40F.

So maybe crud in the matrix is keeping others from getting enough heat?


Norm
Norm Kerr

I thoroughly cleaned my heater matrix and less than 2 years later flushed it through again (don't ask) so I know it should be preety clean

Norm TBH I'm not as hardy as you, more often than not the hood is up in the winter

The main reasons are that I don't like to fold the hood if it's too cold and putting the hood cover on is a phaff when cold, I got too used to the ease of the Mx-5 roof with a glass rear window, if I was taller I could have raised or lowered the MX-5's roof from the drivers seat within 3 seconds

But I do enjoy roof down driving when it's a bit nippy as it feels so fresh, I do need hat and scarf though
Nigel Atkins

one thing about flushing a core, you might have already done this, but just in case:

If you have a radiator shop do it, they will de-solder the end tanks and run a rod down each of the little tubes. They are able to clear out clogs that couldn't be removed otherwise.

I've seen them remove junk from radiators that "looked" perfectly clean, because the gunk stuck in there blocking whole sections of the radiator wouldn't come out by mere water / chemical flushing, so the water would deceptively run clear and clean.

Norm
Norm Kerr

Yes good idea (dependent on cost) or replace with good quality new ones

As my rad and matrix worked well when I got the car (rad was 5 years old) I thought I'd try just a thorough clean of both

Both now work too well at times, although the rad heats up fairly quickly when stationary (normal for my model I understand)
Nigel Atkins

I totally agree with Guy.
Once the car does a certain speed the heaterfan is useles.
I only switch it on when im in a trafficjam and see the watertemp. rise.
It sucks out hot air from underneathe the bonnet and also warmth from the heaterradiator when it blows thrue it.

Otherwise not realy usefull to me.
Arie de Best

Ah, but the fan is WORSE than useless if the motor is rotating in the wrong direction. Ask me how I know!! At that point, it keeps the air from flowing in. I distinctly recall reading in one of the usual manuals that you should turn on the fan, verify direction of rotation and reverse the polarity if necessary. It specifically stated that the wire colors may or may not be "right". That is the part that I read after laboriously fixing my heater fan and switch in preparation for a Missouri Endurance Rally one cold March weekend. After freezing all weekend, I found that the fan had been rotating backwards the whole time, negating the heater's effectiveness at any speed. Added to the fact that my front u-joint started to fail when I left my house and there was nothing I could do about it for the next 2200 miles, it was not the most pleasant weekend. Memorable, yes; pleasant, no.
David "at least it is better than an MGB heater" Lieb
David Lieb

I added a relay to the heater fan circuit and it made a noticeable improvement in the fan speed. Still not a Volvo heater, but then I don't drive her much in the bitter cold.
Lee Fox

Until I bought my basket case a couple of months ago, I haven't owned a Midget for more than 15 years, but my memories of two separate Midgets is that the heater was extremely powerful - too powerful in the average British winter, but not now I imagine! Certainly much better than any MGB heater.
Mike Howlett

Mike
- the Midget heaters do still get too hot (well on your leg at least) and are much better than in the B

Even my wife says our heater melts her feet!!

I can confirm they can be wired to go the wrong way

I'm not sure the big and long inlet pip helps matters

I think possibly increased fan speed would make things worse

And yeap beyond a certain speed the fan is redundant
Nigel Atkins

I fitted the intake end of the heater pipe into the plate behind the grill correctly and changed the thermostat to an 88degree one and the heater is much better now. I still don't get a lot of airflow, I will investigate that over the weekend, but at least it is hot air that comes through.
It did get a little cold yesterday. So cold in fact that I had to wind up the windows. If it gets much colder I may have to put the hood up!

Dave
D Brown

I have always found Midget heater putput to be good. I don't recall my MGB being any worse though!
Dave O'Neill 2

That should, of course, read 'output'!

Also, if the fan is wired the wrong way, I think it still blows air, just not as much as if it is wired the right way.

It therefore follows that if you have converted from positive to negative earth (ground), you should swap your heater connections.
Dave O'Neill 2

Dave (B) IF you've got the roof down you don't want to turn the fan on (unless you've got a tonneau fitted)

I don't care I'll state the bl**ding obvious - to check if fan's wired right way round pull the trunking off heater end, check the mesh is there to stop objects getting through, turn fan on, hold a piece of tissue at the end of the flap extention pipe, see what happens

A stationary car test, when the engine has warmed up with just one of the footwell 'doors' (flap) open, fan off, put your hand near the open 'door' it should feel hot not very warm, if not then it's probably the matrix (tap water is not your friend here)

Only other thing is the tap

The uprated B heater matrix will not fit (in and out pipes in wrong position) and I don't think there is an uprated matrix for the Mk3 but you don't need it to be uprated the standard one new or in good condition gives out a lot of heat - moving that heat is a different mater

You can get an uprated motor and fan, I did, but as I put before i've not noticed any difference to the previous ones
Nigel Atkins

Nigel, what does the tissue paper do?
Dave O'Neill 2

Well if all goes wrong you can wipe away a teer or if something frightening happens you can use it elsewhere
Nigel Atkins

Sorry if I make myself look an idiot

but just in case that was a serious question and I appeared rude before

The tissue acts like a flag or wind sock to let you know direction of air flow

Hence don't let go of it if the mesh is missing
Nigel Atkins

Nigel

AFAIK the fan will still produce airflow in the correct direction even if it is spinning the wrong way, just not as efficiently.

As it is a centrifugal fan, it doesn't work in reverse, unlike an impeller.
Dave O'Neill 2

Dave Brown admits to have driven with the windows up...

Dave is a girly,
Dave is a girly,
Dave is a girly,
LOL!!!!
Arie de Best

Keep hold of the tissue, wire other way round see which works best

The info was posted further back but you're quite right I should have put this bit

I was doing two things at once and I know I can't

And I was shocked that Dave Brown has kept the glass for his windows - rules him out of the Iron Man contest
Nigel Atkins

I am a bit embarased now, admitting that I wound the windows up! It was bl**dy cold and I did have a 60 mile round trip. That just sounds like an excuse, doesn't it?
Perhaps I should just keep my head down for a while until you all forget about it ;)
Now Nigel, how much weight will I save by removing the glass and winder mech from each door? What else can I get rid of? The spare wheel has already been discussed at length on the forum. Tool kit? I have RAC cover to get me home where I keep the rest of the tools. Passenger seat? Passenger side section of the dashboard? Trim, soundproofing (if I had any)? replace the windscreen with aero screens, quarterlights, hood and frame - it only gets used when it rains.

Have a good weekend in the snow and I don't want any of to have the hood up or the windows.

Dave
D Brown

Dave I wasn't think of weight saving - when you're my weight you don't worry about power-to-weight if you're in the car

I was think of taking away the temptation of putting the windows up

This time of the year if the top was down on my car the windows would be up and probaly heater on

Not that the top would be down often - I'm now old and cold
Nigel Atkins

You will loose weight when driving open in freezing cold weather. You will burn more to stay warm. (Look at Arie).

Flip
Flip Brühl 948 frog 59

My heater works perfectly, now. I made the mistake, not yet mentioned on here of connecting the heater flap cable incorrectly. ie.When you push it, it opens the flap. I had connected it so that it pushed the flap closed so the heater output, whether forced or natural was rubbish. It was only because I'd remembered how good the heater had been before my restoration that I questioned it. When I investigated and discovered my mistake it was a simple job to do it right and the heater now works very well and can sometimes even be a bit too hot. So it is worth just having a look to see if your flap is operating the right way round.

Bernie.
b higginson

Good one Bernie - it may not be that but easy and quick to check (and rectify if it is)

Dave I'd like to hear if you've solved it and how
Nigel Atkins

come on girls stop your moaning, dress for the weather, the heater is nothing more than a head ache and a drain on the battery. Rip it out and buy a gimp suit. I drive on un treated roads to Llandrindod Wells ( the coldest recorded part of the UK ) without a heater while still keeping that Midget grin in place. drop the roof down, grit your teeth, know you're alive or buy a Ford!!!!
Nick Sayle

You're spoilt Nick, untreated roads and no traffic (to speak of)

Are you still able to drive on one of my favourite roads Beulah to Tregaron

This year my mate found a pub he enjoyed near Tescos in Llandrindod Wells, we missed it wgen we joined as we had to get to Llandovery for another visit to the Red Lion unfortunately it was shut despite my best efforts with one of the brothers but we spent a great time in the Kings Head Inn talking with a chap that arranges classic rallies in the area

We then made our way to Royal Oak, Rhanddirwyn for our overnight stop as a start to another excelent tour of Wales

Roof down, heater off - but it was end of September
Nigel Atkins

Beulah to Tregaron mountain road was designed solely for the MG Midget, it's a real drivers road
Nick Sayle

Dave - did you get this sorted?

Nick - >>Beulah to Tregaron mountain road was designed solely for the MG Midget, it's a real drivers road<<

The excess of loose chippings and low exhaust manifold slowed my progress this year but still a lovely drive

My mate was in his Supra and had just come off the weekened tour of the area but it didn't include this road !!

They stopped at the green painted "car" hotel in Llandrindod Wells, not my type of place, but they did find the pub near Tescos
Nigel Atkins

Hi, Nigel,
yes it is nearly sorted. I fitted the trunking correctly which made a difference at speed and fitted a warmer thermostat which has improved air temperature. I still need to look at the fan to make sure that is performing at its best.
While the engine was being rebuilt in the summer I cleaned the heater matrix and replaced the foam so I think that is all ok. I got a lot of rusty water out of the heater matrix and hope that is all that was needed.

Dave
D Brown

Good news - sounds like if you ever need to have the haeater out again another thorough claen and flush m and back flushing might help (but it might not)

Last Sunday (at around plus 8 degrees) mine was running at not much off C but still hot air from heater so it looks like I need to put a couple bits of cardboard at the sides of the rad grille for the sake of warming the engine when running

At least I know the rad is cooling well and so it should after two good cleanings an a few unwanted emptyings
Nigel Atkins

This thread was discussed between 29/11/2010 and 09/12/2010

MG Midget and Sprite Technical index

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