MG Car Repair: 1979 mgb temp guage, bench test, fuel gauge

Question
gauge runs almost to red.
last year it was fine & stayed in the middle.
i have replaced the sending unit ,the step down voltage relay
the thermostat and the fan switch senor.
the engine is not over heating. i have checked with a heat gun.
how can i check gauge with buying a new one?

Answer
Hi Chuck,

Before you buy a new gauge try a few little tests first. Use a analog volt meter and test the out put voltage to the gauge from the voltage stabilizer (light green w/green tracer wire) with the engine running and with the engine not running. It should be about 10v. Also test the charge rate by just checking the voltage at the battery with the RPM at 1500 to 2000 RPM. It should be about 13.8v to 14.5v. Anything higher will effect the gauges (temp and fuel)

Also test the ground on the gauge to see that it is a good ground. Also, does the fuel gauge read correct? The fuel and temp gauges are the only things powered by the voltage stabilizer.

I don't have a good bench test of the gauge itself but if the ground is good and the voltage stays about 10v and the fuel gauge operates correctly and there is no over charge from the alternator, the only thing left is the sending unit and the gauge itself. It is highly unlikely that the new sending unit would be off in the same manner as a old sending unit.

If all that is correct you might e-mail Nisonger (info@nisonger.com) who rebuilds most British instruments of Smiths and Jaeger gauges. I don't remember what brand the temp gauge was in the 79 "B" but if it is Smiths or Jaeger they should have a bench test for the gauge itself.

Howard