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MG MGA - Temp. gauge malfunction

The temp.gauge on my mate's 1956 mga roadster, has suddenly stopped working. The needle on the gauge is permanently stuck at 160 degrees. The needle does not move up or down from 160 even with a very hot engine. It was noticed that if the glass face is removed, moving the needle up or down away from the 160deg mark, the needle springs back to 160.
The long pipe running from the back of the gauge to the temp bulb on the engine seems to be leak free. The gauge worked perfect up to a few weeks ago. Can anyone put some light on this problem. Any help/suggestions will be very welcome.

Frank
F Camilleri

I don't know what's wrong with it, but when you open it up this is what you find inside: http://mgaguru.com/mgtech/dash/dt105.htm
I will take a wild guess that the finger which is attached to a solid anchor point had come loose.
Barney Gaylord

Frank,

I will bet it is the hair spring on the pointer shaft which has broken while at 160 deg and has developed a new temporary anchor point causing it to return to 160 after deflecting the pointer a little.

Design of these gauges is quite simple and normally robust. The most delicate feature of them is the pointer return hair spring.

Once the gauge is out of the car and on the work bench you can dismantle one in minutes by removing the two sets of three 5BA screws (oil and temperature). However replacing the hair spring could be a challenge. I've never done one myself but I'm sure a watch repairer would be competent to do it if you don't fancy the job yourself. The outer end of the spring is anchored by a pin which could be reused but I'm not certain how the inner end is fixed.

On the other hand I may be completely off target!.....................Mike
m.j. moore

That is very kind of Frans Camilleri to share my problem on this thread. I have managed to get hold of a working Smiths instrument and would like to know whether it is possible to exchange facias. On our island we do not risk a temperature gauge not working!


c vassallo

Yes it is possible, you have to gently pull the needles off, a watch repair guy will be able to do this. Then the face just lifts out. Put the bulb in boiling water while replacing the temp needle so that you can put it on at the right calibration. Be careful to pull the needles straight off the shafts in order not to snap the shaft by bending it as you pull.
dominic clancy

Thanks everyone for your information. I shall give this operation a try and will come back with the end result.
c vassallo

I have managed to find the problem with my temp gauge which had the tube broken from where it connects to the bulb in the engine block. I did succeed to replace the Jaeger facia onto a working smiths instrument. I have taken the car for a couple of spins and all looks fine. Thanks to everyone's contribution.
c vassallo

What a great idea, I have a good Smiths gauge and a Jaeger one that has a bad nut on the bulb end. Don't know why I never thought to change faces,Thanks
gary starr

This thread was discussed between 28/09/2013 and 17/10/2013

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