water temp guage on a '62 A-4

[JimH]

The A4 on my 1962 Pearson Triton has worked flawlessly, but in the four years I have owned it the water temprature guage has never worked. the needle is stuck permanently at 120F...so I convinced myself that the engine never over heats. Time to install a new guage.
I removed the old guage and found that the sending cable was missing and three electrical wires conected to three wiring posts in the back. The new guages I have seen all have cable and sender unit with bushings of different sizes to connect to the engine block. The only electrical wiring is for the instrument light. Where on an early A4 does the sender connect with the engine? What explains the old guage? I should mention the my engine does not have a thermostat. Will the 2" guages sold for cars do the job?
Thanks for all your help.

[Don Moyer]

Jim,

Your early model engine would normally have had a mechanical gauge with a long sensing tube running to the engine itself, frequently into a "T" fitting installed into the rear outlet of the manifold.

Late model engines use electrical instruments which connect to an electrical sensing unit threaded into the front of the head. You can use the same type of gauge in your early model engine by installing the electrical sending unit in the same location as the sensing tube was installed for your direct reading gauge. If there is currently no evidence of any sensing tube attaching point on your engine, you can install a "T" fitting of the appropriate size for the electrical sending unit in the rear outlet of your manifold.

In theory, electrical sending units are electrical resistors which vary the resistance to ground as temperature rises and falls. The gauge in the cockpit interprets this changing resistance to engine ground and converts it to the temperature value.

I'm attaching a guide for testing electrical gauges which may help you to understand the process.

Don