The Stewart-Warner Speedometer Corporation and

Origin of the WARN –O- METER



Arthur P. and Charles H. Warner of Beloit, Wisconsin founded the Stewart-Warner Speedometer Corporation.  The corporation actually began in 1903 as the Warner Instrument Company.  The company’s first successful product was the “auto meter,” an improved version of a speedometer. The Stewart-Warner Auto Meter was more accurate and durable than competitor versions and quickly became an industry standard for most automobiles.


In 1912 the Warners sold their company for $1.8 million to speedometer manufacturing rival Stewart and Clark Company of Chicago, Illinois.  The new company was renamed Stewart-Warner Manufacturing Co.


Eager to grow quickly, in 1913, the Stewart-Warner Speedometer Corporation (S-W) had one of its employees, (engineer Edward A. Larson) who attended the National Auto Show held in New York City’s Grand Central Palace (January 3 – 10), procure an early version of the Motometer Company’s radiator-mounted motor heat indicator trade name branded the BOYCE MOTO-METER.  Larson was a direct report to S-W management.


After dubiously acquiring the engine temperature indicator Larson set up a series of meetings with Motometer Co. president George H. Townsend II to uncover just how the device worked.  Once he had gained enough information S-W set about reverse engineering the Moto-Meter and constructing their version.


Shortly after Harrison Boyce received his Indicating System and Apparatus for Internal Combustion Engines Patent (March 17, 1914) S-W, in April, commercially released its “Auto Thermo-Meter” based on Edward Larson’s Automobile Radiator Thermometer patent.   Taking notice of the Auto Thermo-Meter’s very public commercial release in industry-leading trade publications like Motor and the Automobile, Harrison Boyce filed lawsuit seeking an immediate injunction against S-W along with suit for patent infringement.


Once the preliminary injunction was granted Stewart-Warner was required to immediately halt sales activities and to remove them from the auto accessory market.  Harrison enjoined the Motometer Company into the patent infringement lawsuit and they eventually won on appeal.  This marked a monumental moment for the Motometer Co.


Almost ten years later, in 1922, Stewart-Warner Speedometer Corp. re-entered the motometer accessory market with its electronics-based “Warn –O– Meter.”  The Warn –O– Meter was invented and patented by Frederick G. Whittington of Chicago.


The Warn –O– Meter is readily identified by its five-sided, pentagon shape; three holes in a triangular pattern below the main frame housing; and, in most instances the winged Stewart-Warner logo and Warn –O- Meter name on its glass lenses.


The Warn –O– Meter could be attached directly to an automobile’s radiator cap and radiator though not necessary as it made use of a temperature responsive circuit that once completed would send an electrical signal to the actual gauge and its light panel system within the gauge.  The temperature responsive circuit attached directly to the side of the auto’s engine and was not exposed to the radiator or coolant.


Once the circuit was tripped the internal lights would begin to illuminate a red cellophane panel changing from green (normal operating temperature) to pink (temperature rising) and eventually full red when indicating elevated or dangerous engine overheating temperature condition.


This arrangement, in the use of electric power, a bi-polar switch and a light panel-based temperature range indicating device was quite novel at the time and enabled it to be placed just about anywhere on or around the auto’s engine cowl or fenders unlike the radiator-mounted versions, like the BOYCE MOTO-METER.


Another of the Warn –O– Meter’s professed virtues was that it could be easily read, day or night and “flashed red before Motor overheats” and that it “takes the motor’s temperature from the motor itself.  Not the water in the radiator” according to company advertising literature.


The Warn –O– Meter could be purchased in three model versions – a DeLuxe, Standard and Ford model.  They retailed for $12.50, $10 and $10, respectively with the DeLuxe available in nickel-plate finish while the Standard could be had in either a back enamel paint or nickel plate-finish. 


Strong evidence exist that the Stewart-Warner Speedometer Corp. was first, in 1914, with its Auto Thermo Meter, to introduce personalized motometer auto manufacture script logo nameplates, (notably for the Marmon and Mitchell companies) approximately a year before the Motometer Co. employed the practice with Mercer, then Haynes, Packard, Stutz and Simplex logo motometers. 


In 1922, to enhance the appeal of the Warn –O– Meter, Stewart-Warner offered purchasers the opportunity to receive personalized plates with the initial of their choice. Free of charge a Warn –O– Meter purchaser could receive an entire alphabet set of initials for their installation.


Most Warn –O– Meters that come available for sale in today’s market spaces are Standard types that once had the black enamel paint finish.


The exact number of Warn –O– Meters that were manufactured or sold is not known, though truly never or very little used and fully complete examples are few and far between with only one full set known to exist.


When the automotive accessories giant Stewart-Warner Speedometer Corporation lost the patent infringement lawsuit to Harrison Boyce and the Motometer Company it established a monumental precedent for Harrison as his fundamental patent was upheld as legally court validated and blocked other competitors from entering the motor heat indicator market for years to come.  The advantaged gained by the Motometer company would not be diminished and would only grow.  Stewart-Warner Speedometer Corp. would also be the first of many companies to lose patent infringement lawsuits to Harrison Boyce and the Motometer Company.


Notwithstanding the Stewart-Warner Corp exists to this day and is an automotive parts, accessory and component supplying juggernaut.



SINCE 1912