Motometer vs. Temperature Gauges

Although I have not been involve with Model A’s as long as many have, I have heard horror stories and seen some myself of what high temperatures in an engine can do.  I have had both a temperature gauge and a reproduction motometer on my Town Sedan ever since I have owned it.  Only once have I ever seen the red mercury show up in the motometer.  That was when I had a problem with the radiator and the temperature gauge was spiking over 190 degrees.  We quickly stopped the car to save the engine and let it cool down.

Even though I have heard the argument that many people ran the Model A’s for many of years without temperature monitoring devices, I find it difficult driving a car without a temperature gauge.  One of the key indicators to me if an engine is OK is knowing the temperature range that the engine is running.  When you install the temperature probe of the temperature gauge in the upper water neck or in the upper hose with the adapter pipe, the probe is always in the hottest water of the engine.  This is a plus for the temperature gauge unless the system is dry; it should always be in the water stream.

A motometer can fail you at times if the water level becomes lower than the probe extends down.  I have also seen where the mercury will divide and a false reading will occur.  To depend on this form of information may create a whole lot of problems that may not really exist.  As in my case, the motometer never shows any temperature until it is too late.  By the time my motometer shows that the water is hot, I may have already created warpage of the engine head or worse, I have scored the cylinder walls.

With the cost of a temperature gauge, approximately $50.00, versus not having one and having to rebuild an engine, it is my experience that a temperature gauge is a small investment to protect the larger investment in an engine.

This tech tip was originally printed in the October 2001 “A” Quail Call.

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