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MG Midget and Sprite Technical - Intermittent overheating problem

Any ideas anyone? Been on a run today with a local club over to the Cotswolds (pic attached of my pride and joy parked outside of the Cotswolds Motor Museum in Bourton on the Water).
There and back, I suffered an intermittent problem of the temp gauge being right up in the "H" section for significant periods of the journey. This was independent of road speed, air temperature, gradient etc etc. Then all of a sudden, the temp would return to normal! I checked the water level when we arrived and it was about an inch low in the rad, after driving about 100 miles. I topped it up before leaving for home and also set the thermoststat on the electric fan to come on much earlier than normal (usually set to come on just after "N"). However, the journey home was just as troublesome, with the gauge soemtimes indicating normal temp variation and sometimes showing the engine was way too hot :( . Fortunately, the car performed perfectly without any misfiring or loss of power and we got home safe and sound.
I'm thinking perhaps the thermostat is playing up (but it was only replaced 2 years ago) or could there be some sort of blockage in the rad or the head that is moving about?
PLEASE HELP!!
Glynn


G Williams

Faulty gauge?
Guy W

Ok, that did enter my head but is that a known problem? To be honest, judging by the heat coming from the heater flaps in the footwells, I reckon the actual temperature was as indicated - i.e bloody hot!
Glynn (not Glenn) Williams

change the thermostat cheap and easy see if it improves. When was the cooling system last flushed out? Is it full of crud stopping it working correctly?
I Pickering

If the ONLY evidence was what the gauge showed, then it would be a possibility. But if there are other symptoms, then probably not. Sorry.
Guy W

Glynn,
if your antifreeze/coolant is more than a few years old and you haven't done a thorough clean and flush of the coolant system then it would help to do so and even if not the cause of your problem doing this should help you to find the cause

I've got notes on a simple but thorough method of coolant system cleaning (and overhaul as required) that I use and my engine runs very cool but heating very hot, just email me if you want a copy

there can be an amazing amount of crud in you engine, rad and heater but particularly the engine that can be sitting around and then dislodge
Nigel Atkins

Thanks everyone for your advice. The antifreeze was changed severla times when I first got the car abck up and running but is probably about 2 years old now. There might well be crud floating around as the car was idle for long time before we breathed life into it once more.
Nigel, I have just emailed you as suggested for a copy of your method and will read that with interest.
IP - I might well change the thermostat and the antifreeze too. As you say, it doesn't cost a fortune and yesterday I would have paid the Earth for assurance that I was not going to blow my head gasket before getting home!!!
Glynn
Glynn (not Glenn) Williams

I am still getting crud out of mine and plan a 'final flush' before the winter when all water loss is confirmed as stopped (a weep from a PO bodged tap will be fixed soon). I am now finding it impossible to overheat my 1500 in the hot days in traffic and the heater is not as hot as I would like. This is all down to flushing, flushing and flushing.

At one point I thought I had flushed enough (twice) and then lost a lot of water when the crud moved around when I drove it hard. grrrrr. Car was off the road for nearly ten years till Christmas last year and coolant was left in for that time.
Dave Squire (1500)

Dave,
don't you mean repeated flushing/back-flushing/flushing :D
Nigel Atkins

Hi Glynn, must have been something in the air in the Cotswolds, my 1275 Hif44 converted midget started to misbehave in a similar manner yesterday too!
Run up from the Isle of Wight to Prescott hillclimb. About half way, the temp gauge would very slowly rise until the electric fan cut in (driving at speed! that's never happened before) Temp gauge would then slowly fall to normal. Cycling like this at speed, when running a bit slower (55 - 60mph) all OK.
Before the return trip, I checked the plugs, they were running lean, tweeked the mixture (plus 1/4 turn) and all OK for the return trip.

In your case, I would change the thermostat, flush and check your timing and mixture too.

Regards Tony





Tony G

While you putting in a new stat... drill 1/8th inch hole in the stat face ... that will keep from an all out blockage if the stat fails to open

Remember... stats are now all made by 8 year old little girls in china, making 25 cents a day, do you trust her, i dont

Prop
Prop and the Blackhole Midget

Indeed I do Nigel, it is the back flushing that I do do and I use 'flush' each time. And I take the radiators (both) out and flush them separately.

Dave Squire (1500)

I would echo previous comments to change the thermostat and flush the rad. Easily done and cheap. I would not rule out a faulty gauge. My 1275 kicks out plenty of heat from the footwells even when the gauge is to the left of N.

That said, try looking arond the carbs for leak or a loose hose or something which would cause a weak mix, and would subsequently cause the car to overheat. Blockage in the jets would cause similar - good squirt of carb cleaner - or crud in the float bowls - drain them...

Superb colour of car by the by. Very nice...
Mark O

slight thread drift warning for the engineer types that worry about such things ;)

Dave,
sorry I was preaching to the converted :D
I'm a bit concerned about your heater not getting very hot, thoughts;
. is the heater tap itself or heater tap orifice reduce by crud accumulation or build up
. is the tap the correct way round (on is on and off is off, altho' I don't if it can be fitted wrong)
. I have seen hoses connected the opposite way round
. did the important foam seal around the matrix get replaced if required
. same for foam washers on pipes inside heater box and/or grommets on pipe holes in case
. and the important seal from bottom of heater box to opening in car body
. have you got the fresh air tube flap set correctly so that it's fully open when the 'H' button is pushed fully in on the dash

if you just have the driver's footwell flap open and passenger side closed then the heater should melt the polish on your boots and swell your feet so that you can't get them out of your boots to cool them down at your next call

if these 1500s are supposed to get so hot then their heaters should be hotter than mine which will not get turned on again until winter
Nigel Atkins

Thanks everyone for the tips - plenty to go at on the weekend. Particular thanks to Nigel for sending me his method sheet.
I love this forum!
Glynn (not Glenn) Williams

This thread was discussed between 01/09/2013 and 02/09/2013

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