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MG Midget and Sprite Technical - Temperature Gauge

Hello Group more help please - the temperature gauge on my Mk3 moves as the engine warms but never goes further than halfway between cold and N even on a hot day or in traffic - is this normal if not where do I start sorting the problem
P Willoughby

remove the sender from the head and test it in a kettle of boiling water to see if the gauge is OK.
David Smith

In the winter mine usually sits two thirds of the way between C and N - and that was with the old guage and the new replacement guage

but, sorry,

sounds like it may be time for a replacement, only test first of course
Nigel Atkins

Thanks for the advice so far - what should a gauge read when the sender is placed in boiling water
P Willoughby

depends on the gauge, early Mk3s = 212 and later ones = H
David Smith

Might not have a thermostat in the car?

My midget 1500 was running no more than 1/2 way between C and N, I suspected the oft removed thermostat and sure enough it wasn't there. Once fitted (an 82 degree one) the gauge stays no less than 2/3 between C and N when warmed up fully.
RoadWarrior

hi Guys.. here's my sixpen'th

the guage on my old 1275 reads a rock steady 175 F












until I sit in traffic!
David Cox

Just waved the lady of the house off shopping then made a beeline for the kettle and tested the sender - had it boiling away 212/F and the gauge read just over N,up on normal running reading, there is a new themostat fitted. From that can it be said to be reading correct or a bit slow. I have wiped the oily finger prints off the kettle so her indoors will non the wiser (fingers crossed)
P Willoughby

That sounds about right (IIRC the 212 text is around 5am on the gauge).

It seems that all cars have slightly different characteristics on these things, and I suggest your reading is in range of normality.

A
Anthony Cutler

How about your "rad" cap being wrong or faulty should be a 15lb/in, if standard car, only a few quid to change

Just looked at your profile photo, smart car

I think the black plates would have been illiegal in 1973 (IIRC) let only 2073 :)

On a serious note, as they say, if you're ever going to park your Midget on a street at night I'd recommend swapping to refective plates so the car stands out to the lights of oncoming traffic plus when on the road you want as much illumination (and reflection) as possible on the rear of your car

I remember going down the A14 at 70 mph then almost before I knew it bearing down on a MGA with tiny dim rear lights and black plate (going at 45 mph), modern bycycle rear light would have been more noticable, good job both rear lights on the MGA were working or I would have thought it was an old bycycle light

Compare 1973 Midget rear lights with even a low cost modern car - safety talk over
Nigel Atkins

Late Midget rears lightsare a damn sight brighter than MGAs and they have bigger reflectors. I take your point on black number plates but they suit our wee beasties so much better than reflective ones. My 73 also illegally sports pressed aluminium black plates although I do keep the originals in the boot just in case......
My concern is not so much someone running into the back of me in the dark as I try not to hang around, but in the fog and I would be tempted by fog lights if I saw any that looked OK.
Matt1275 Bucks

... have to disagree with Ant - boiling kettle should be in the H white sector on the gauge (not N). There's no way a boiling temp can be regarded as normal. Norm is 180 and the hot sector goes from 212 upwards as far as the pressure cap will allow.


David Smith

If you look closely at the dial of the gauge you will see that there are two pairs of small calibration marks on the face. I believe that the upper pair is where the needle should sit when at boiling point (atmospheric, not pressurised). The needle can be pulled off the spindle, turned and pushed back on to match this reading. Its also possible to alter things internally as there are two screws that secure the mechanism and this allows for some adjustment. That said, they generally seem to work or not work - with nothing in between.
Guy Weller

Mh, mine rarely goes over 160, unless traffic or shut down. Hung the bung in boiling water and needle went up to almost the "hot zone".
Never knew this was ok, untill now, thanks guys.

BTW, IMHO, 160 is ok, cooling system is in order then.
Alex G Matla

Using Dave's photo of the dials mine would sit at 160 too normally plus also the photo reminds me where 5 would be on the guage I was think of 7

And Dave has already said that 212 is near to H

So back to "rad" cap or guage (or slugde/blockage or airlock or something obstructing the rad or?)

(I've never asked but always wondered about the dots on dials, thanks Guy)

Matt
- lights, yeap I agree that later Midget rear lights were better than MGAs, a friend has a Rover P5 big car but little rear lights, I used to have a Rover P6 and was glad of the large reflective rear number plate as that had smallish rear lights too
Nigel Atkins

Guy,
If the needles should sit at boiling at the upper calibration dots, what do the lower pair signify as that's pretty much where my needle always sits. i.e. pretty much halfway between C and N. I keep on meaning to actually check what temperature thermostat I've got or indeed do the kettle test on the bulb but am slightly loathe to start buggering about with the thermostat elbow stud issue when all seems to be running fine anyway.
Matt1275 Bucks

Hi David

>>... have to disagree with Ant - boiling kettle should be in the H white sector on the gauge (not N).

I said earlier that:

>>That sounds about right (IIRC the 212 text is around 5am on the gauge).

In response to:

>>made a beeline for the kettle and tested the sender - had it boiling away 212/F and the gauge read just over N,up on normal running reading



Isn't 212F the boiling point of water at sea-level? (180 + 32 degree offset?)

212 is approx at 5am on gauge? (maybe 4:30am?)

Of course with a radiator cap and pressure at 8lb (earlier?) and 13lb (later), the cooling system under pressure would boil at higher temps, e.g. 220 or so?


So I concluded that car was running in bounds of normal temps, around 160F to 180F (when slow/stationary); same as my Aseries and now Kseries (of course I have the 'dumb' dial on my gauge).

A
Anthony Cutler

This is getting like the heater tap debate

"Rad" cap should be 15lbs/in (and 7 for earlier models)

David's photo shows 212 as being close to H on the other gauge so that would seem too hot

Mine would at 160 (7 am) for normal running 212 (4.30/5 am) would have me very worried

Anyway P what's the outcome
Nigel Atkins

Different sending units (at least the 1500 electrical ones) can and do give wildly different readings. I've a pair myself that read at least 20 degrees apart (12:30 or 2:00). I'd assume the same be might be true with the earlier design as well, making gauge readout a relative notion, at least until "calibrated" as per Guy's advice above.

If it ain't on fire, keep driving!
Richard Reeves

Yeap if you've had your car for a while and know it's working well then you know what reading the dials usually give but if the car is newish to you then it's best to check

the earlier cars were not electrical guages but certainly can flicker around

plus the earlier cars have a combined water and oil gauge that are a bit more effort to remove and refit than the electric guages
Nigel Atkins

This thread was discussed between 30/06/2010 and 02/07/2010

MG Midget and Sprite Technical index

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