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MG MGB Technical - Heater booster function

Whilst flushing through the cooling system on my MGC today I discovered when flicking on the cockpit switch to the heater booster that nothing happened.

Fuses appear OK. Does anyone have any ideas what could be the problem?

Thanks very much for any advice. Very much appreciated.

John M
NE England
JP Mitchell

ignition switched on?
Nigel Atkins

On a B for certain years (about '70 onwards)the fuse is an in line variety but situated close to the fuse box. Green with pink wire. It also supplies the wipers-did they work? Ignition switched)
Michael Beswick

Do you mean fan speed 2?
Allan Reeling

UK MGBs from 1971 for the remainder of chrome bumper production powered the heater and wipers from the accessories position of the ignition switch, which has its own fuse - white/green to green/pink. Before and after that it was powered from the green circuit fuse in the main fuse box so the ignition has to be on.

It's likely that MGCs would be the same, but as they were produced from 66 to 69 it should be powered from the green circuit i.e. ignition. If other ignition fused circuits like wipers, brake lights, reversing lights and instruments are OK there must be a break in the circuit from wherever the green going to the heater fan switch joins to the rest of the green circuit, which varies according to year, or from the heater fan switch to the motor, the earth from the heater motor to the body earth (also varies according to year, or the switch or motor themselves are faulty. Testing with a voltmeter or test-lamp required.

The 2-speed heater fan didn't arrive until 77, but could have been retro-fitted of course. As the heater gives an output as good as it gets when I at least am driving along, I also tend to regard the motor as a 'boost' facility, e.g. for when stopped in traffic to clear the screen etc.
Paul Hunt

Exactly Paul, the term "boost" is not a common one associated with our heaters!! If the fan or blower is not working at all then it's got to be a circuit, switch or motor problem. Take the motor off and see if it moves freely, if it does test it on a 12 volt supply. Remove the switch and test that. MGC's have only 2 fuses, if the one controlling the heater had blown the wipers, gauges, washer or brake lights wouldn't work either.
Allan Reeling

Gentleman,

Many thanks for your responses and I have digested the content for future reference. Strangely enough I found two areas at fault, firstly the bearings had gone on the motor and secondly when I test-fitted a replacement motor,...found the toggle switch faulty. Only last week everything was fine!!

My C is a 1968 and the fan motor popped out very easily with just three screws holding it in. It came out with the fan attached so a big argument for not fitting a larger fan to the motor if overhauling the heater box.

The other bit of advice I may give is when ordering a new motor (readily available from Moss UK) order a new original size fan blade to come with it. If you try to remove the old one to fit onto the shaft of the new motor, invariably they snap or break.

Thank again very much for your individual advice. Much appreciated.

John M
NE England
JP Mitchell

"...found the toggle switch faulty"

If the bearings had caused the motor to stall or run very slowly, you get a much higher current than normal, and that could have affected the switch.
Paul Hunt

In the 13 years I've owned my 79 MGB, the heater or should I say warmer, has not been very forthcoming with heat. The 2-speed fan really doesn't create much flow either.

Cheers

Gary
gary hansen

Gary,
there could be many reasons and a combination of them to why your heater isn't as good as it could be

electric - connections, wires and switches not fully clean, secure and protected (from fuse and fusebox onwards)

tired fan motor

problems with cable or connections from heater switch to heater flaps and valve

heater box not fully sealed to car and matrix to box and/or with debris inside stopping heat from matrix and efficient working of heater 'fan'

partially or blocked air intake (very unlikely)

coolant system not fully clean and free of debris/muck/gunk/grit including heater matrix, incorrect 'water' stat, heater valve not set to fully open and partially blocked inside and aperture in block

insulation to car including door/window and fresh air flap seals that let hot air out and cold air in

or possibly over the years your expectations have grown inverse to the function of the heater
Nigel Atkins

Another thing that can help is that when you have the heater motor out (and assuming that you can move the blower cage on the shaft), adjust the position of the cage so that it is as far away from the motor (i.e. towards the firewall) as possible without rubbing the rear of the heater box. The more space you have between the end of the cage and the rear of the heater box, the more opportunity you have for air to spill around from the outside of the cage back to the center (from the "output" back into the "input" -- recirculating *within* the heater box).

I'll also second all of Nigel's comments, with special attention to the thermostat. Many owners fit too-cool thermostats (especially in hot climates) to address an "overheating problem" when in fact: 1) a cooler thermostat doesn't help with overheating, and 2) they don't have a problem to begin with.

Florida is not that much hotter than NC and I run a 195ºF 'stat year-round. My car has never overheated. The gauge will sometimes approach 'H' but that's not overheating and not a problem! And my heat is nice and toasty, albeit the volume of it still lower than I'd like.
Rob Edwards

having the foam seal around the matrix fitted correctly and in good condition and with the heater box seal ties in with what Rob has put

I'm also not a fan of oil coolers being fitted as they often over cool, if an oil cooler is fitted I think it should also have an oil thermostat fitted
Nigel Atkins

There are a dozen or more factors that can contribute to insufficient heater output. I've done no work on mine apart from reverse the motor wires on the V8 when the movement of air was patently less than that of the roadster, but at around 10C/50F I get just over 60C/140F out of mine, which burns our feet. Oil coolers on both. You might like to have a look at http://www.mgb-stuff.org.uk/heatertext.htm
Paul Hunt

great link to your excellent site

I've just posted another link to your site on another thread

IIRC on your site somewhere you have it that you don't necessarily need an oil cooler or have posted as much (or I might be wrong about this)
Nigel Atkins

FWIW, my oil cooler has been hanging in the barn for years. Upper 90s F are the norm here in the summer, and low 100s are not that unusual....
Rob Edwards

A current "fad" is to insulate the inside of the heater box. Don't know if this is effective or not!! But renewing the seals on the direction/distribution flaps definitely improves things. When these are in their usual state of disarray, the best you can get is a "blend" of hot and cold when you are moving.
Allan Reeling

I have often said that in my opinion an MGB doesn't need an oil cooler in temperate climates. On my last 1800 MGB which was my daily driver for 12 years, I fitted an oil cooler thermostatic valve. This lets the oil go through to the cooler when the oil is above about 85 celcius (185 F).

Because of the type of person I am, I would often pop the bonnet on finishing a journey and feel the oil cooler hoses. Even on warm summer days the oil rarely got hot enough to trigger the stat, and the cooler remained out of circuit.

When I built my MGB GTV8 conversion, I looked at the MG Rover RV8 and noticed that no oil cooler was fitted, despite the enormous heat output of the 3.9 litre engine. I didn't fit one to my V8 either and even on the hottest days there is never an issue with oil pressure or over-heating.

Just my observations!
Mike Howlett

I've seen that those that live in hotter lands and have an oil cooler and oil thermostat fitted have found the same as Mike that often the oil doesn't get warm enough to open the oil stat

the point about the RV8 not having an oil cooler was what I was thinking was on Paul's site from Roger (forget surname)'s article

the oil cooler should be blanked off during cold/cooler weather which could include many spring, autumn and summer days

if your B is regularly used to tow big or heavy items or used on race tracks then an oil cooler might be needed but I can't see otherwise, I think they were fitted to give a sportscar image - plus modern oils are/(can be) so much better than 30-50 years ago
Nigel Atkins

My personal opinion is that the MGB doesn't need an oil cooler - in England at least, but it doesn't do any harm. You can cover it if you want to in winter, but it doesn't do any harm if you don't - I never have and I used my V8 in all weathers for a number of years. Just five minutes round the block in the roadster yesterday was enough to get the oil pipes warm with an 8C ambient, by which time the coolant had only just got up to temperature. You can fit a thermostatic valve to the cooler, but it doesn't need it, and it's something else to leak.
Paul Hunt

I agree I wouldn't lose sleep over whether an oil thermostat, oil cooler or blind is fitted but oil works its best within a certain temperature range

as always each to their own and it's not a serious matter

I do wonder with 1800 engined Bs that get very infrequent and only very short journeys whether the oil is warm enough and for long enough over the whole of the journey - but I'd guess these cars would be more restricted to warm weather journeys anyway

I've used V8s including a B roadster conversion in winters and in my experience they tend to be warmer quicker

seems to be enough leaks already from oil cooler pipes especially modern made ones or where existing or new ones have scuffed through by lack of support/security
Nigel Atkins

My factory V8 takes longer than my roadster to warm up. That's because it has the 'steam pipe' which is a small-bore pipe from the inlet manifold (which has coolant passages for those that don't know the V8) that bypasses the thermostat. This means a small amount of coolant is circulating via the radiator as soon as the engine starts, and you can feel the top of the radiator starting to get warm almost straight away, whereas the roadster takes longer to get heat and is dependent on the stat opening.

But there are different types of stats that can affect this as well. From the originals with the bleed valve that is open for filling but closes when coolant reaches it and so prevents any bypass, through others with a tiny bleed notch in the valve that allows a small amount of coolant to circulate all the time, to others with no bleed facility that really need a small hole drilling in the surround otherwise you can't get the coolant in, and they bypass more.
Paul Hunt

This thread was discussed between 25/01/2015 and 19/02/2015

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