There was a time when having a thermometer in the car was a luxury. This is how this ingenious invention solved it in the rearview mirror

Today we have basic elements in our cars that have remained almost in the same place for decades. For example: the thermometer. For many years we have been able to know what temperature it is outside from the comfort of our car (although sometimes we wonder if the sensor works as it should).

However, long before this element was incorporated into the instrument panel or the central screen of our car, some manufacturers opted for another place: under the driver’s side mirror. And at a time when analogue predominated, there was no other choice.

The luxury America of the seventies

The analog thermometer in the exterior mirror It was an invention born in the United States, in the context of the great American luxury cars of the seventies. A time when the most prestigious brands in the country competed to offer the most extravagant equipment possible, from Cartier watches integrated into the dashboard to garage opening systems or autonomy indicators.

The mechanism was simple as well as ingenious. And just as they collect On the Curbside Classic forum, where owners and enthusiasts have debated this type of vehicle accessories for years, the thermometer worked using a spiral spring made of a material sensitive to changes in temperature (normally two metals with very different thermal expansion coefficients, such as brass or iron-nickel alloys).

One end of the spring was fixed to the inside of the mirror housing; the other, to the small outer drum. As it expanded or contracted with heat or cold, the spring rotated the drum, which displayed the corresponding temperature on a graduated scale. There were no cables or electronics. It was pure precision mechanics.

Additionally, some manufacturers included lighting built into the fixture, either through a light bulb or fiber optic which came from the dashboard (like in some Cadillacs). This last method was better, since it did not generate heat and did not alter the thermometer reading.

Cadillac first, Lincoln later

The brand that first offered this peculiarity was Cadillac, the jewel in the crown of General Motors. According to they count In The Autopian, Cadillacs equipped these thermometers in the side mirror around 1976, even before its direct rival Lincoln. The Cadillac Seville, the brand’s flagship model at that period, was one of those that included this accessory in its equipment, which was also available in other models in the range such as the Eldorado, the DeVille or the Fleetwood.

From Hagerty Media, in an article about the 1976 Cadillac Fleetwood Brougham, they say that the thermometer in the side mirror was an option available in that year’s catalog at a price of $18, which placed it among the most affordable extras within a menu of options that included everything from cruise control ($104) to the alarm system ($114) or the radio cassette ($239).

The Buick Park Avenue, GM’s other big bet in the premium segment, also carried it from its early years as an equipment package to differentiate itself from the rest. As it appears on the equipment sheetthe original Park Avenue from 1975 already included the mirror with a thermometer along with other elements such as air conditioning and automatic rear leveling in the suspension. For its part, according to account In the middle, Lincoln, Ford’s luxury division, incorporated the illuminated thermometer into its models starting in 1978.

A luxury that is difficult to find today

Just like express the middle the middle, today it is extraordinarily difficult to find these mirrors in good condition. A mirror with thermometer for a 1988 Lincoln Town Car can reach between $140 and $660 on second-hand platforms such as eBay depending on the condition of the part, while one intended for the 1976-1979 Cadillac Seville can exceed $800.

The Lincoln thermometer of the eighties already incorporated the double scale Fahrenheit and Celsius, something that the models of the late seventies did not have, as they only showed the temperature on the Fahrenheit scale. However, Cadillac started getting rid of its analog thermometerssince at the beginning of the 80s they already included more advanced temperature systems in their vehicles where the outside temperature was also displayed in digital format.

The leap to digital

The arrival of increasingly advanced electronic systems made these thermometers obsolete. In the first half of the 1980s, manufacturers they began to integrate digital screens on the dashboards that showed, among other data, the outside temperature. It was the era of “high-tech”, and digital had enormous appeal for the luxury buyer.

The first car with digital instrumentation was the Aston Martin Lagondapresented as a prototype in 1976, although its cathode ray tube technology was too expensive for the mass public (imagine how expensive, if buying an Aston Martin wasn’t exactly cheap in itself). It was the arrival of liquid crystal LCD screens, and in particular the technology TN LCDcheaper and lighter, the one that democratized digital panels in cars during the first half of the eighties.

From that moment on, show the outside temperature on a display inside the passenger compartment. It went from being a novelty to an increasingly common featurefirst in premium cars and, over the years, in increasingly accessible segments. In the mid-nineties, it was already a relatively common element in mid-high range cars.

And if you have ever wondered where the sensor that measures the temperature and that is reflected on your car’s screen is located, usually It’s on the front bumperaway from the heat of the engine.

Seen in perspective, the thermometer in the side mirror was a product of its time, but seeing it today, even in images, gives it a glimpse of very picturesque mechanical elegance.

Cover image | The Autopian (eBay)

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