MGB Register Forum

My temperature gauge does not return to 'zero' when left to go cold. The needle stays mid way between cold and normal. When run the gauge then climbs to midway between normal and hot. Engine doesn't seem to overheat so I suspect a gauge fault. Is it common, and is it a case of a new gauge and capillary tube?

1974 Roadster.

It would appear so. They're repairable but it needs someone who knows what they're doing to carry it out.

I assume it is the dual Oil Pressure/Water Temperature gauge made by Smiths?
For a repair, try Speedycables. They repair all Smiths gauges. See https://speedycables.com/instruments/ga ... nversions/
It might cost almost the same as buying a new dual gauge, which is currently around £124 - £130 inc vat from most of the main suppliers. Whatever you do check the cost of P&P and make sure the price you get quoted includes vat. Also there are many versions of the dual gauge so make sure you are getting the right one for the year of the car.

Should a 1974 roadster have the Centigrade, Fahrenheit, or C N H temperature gauge?

From October 1968 to the introduction of the 'rubber' bumper cars they were fitted with the C-N-H type gauge. If there is a choice you do need a Negative Earth instrument.
Rubber bumper cars used the same 50mm gauges as fitted to Triumphs and had separate water temp and oil pressure gauges.
Hope this helps

Hi Peter,
My 1975 RB has CNH and oil in the same gauge. But I think it was a bit of a bitsa year. I have metal crackled dash with the OD on the wiper stalk. Early tiptronic for me :0)
Other differences are ballasted ignition but with only 1 Relay (Silver Box) next to the fuse box. A bit of both worlds on the change over.

Regards
Paul

Thanks for the advice. Mine has the C-N-H gauge so I will get a replacement.

Hello Steve
Before buying a new gauge you could try adjusting the needle. From your description the gauge seems to be working but the needled seems to have become offset as it reads between normal and C when cold and N and H when the engine is hot. Normally you would expect this to read around the 6 /7 o’clock position when hot.
Try removing the gauge. Easy on a 74 B. Remove the fresh air vent will give you access to the U bracket securing the gauge in the dash. Once out twist off the bezel and remove the glass. (You may have to ease the tags on the bezel)) Then try gently turning needle to read C when cold. Might save you buying a new gauge.
Best regards
Mike Barclay