Temperature tantrum

Date:30 November 2012 Tags:,

Q I have a 2011 GM sedan with an ambient temperature readout on the dash. In a typical day I might drive 15 kilometres around town and make five short trips, but the reading never changes. Our summers sometimes see differences of 15 degrees from morning to afternoon. The dealer says it’s normal. I “fixed” the problem by sticking a piece of tape over the display, but what can I do to make the thermometer more accurate?

A This was a new one to me, so I contacted GM for an answer. Your issue lies partly with how the car works and partly in the way you’re driving it.

Your car’s computer reads the outside air with a temperature sensor, which is normal for pretty much all cars with this feature. However, with your specific car the sensor is close enough to the engine that the vehicle needs to be turned off for at least two hours before the current temperature reading is displayed on startup. This time delay is in place to allow the engine to cool so the heat radiating from it doesn’t infl uence the temperature of the sensor and, by extension, what shows on the readout. Your series of short trips means the engine is probably never off for two hours at a time.

Further complicating matters, the car skews this wait time based on how fast you’re driving. High speeds push more air over the sensor, cooling it quickly, so an accurate reading of the temperature can be made sooner. Cruising around town never overcomes the speed threshold for a real-time reading.

I think you should do some experiments with the car to confi rm this, though. Next time you’re out around town, go off your beaten path and onto the highway for some higher-speed driving. Check to see if the readout is working. Likewise, try waiting over two hours after a shutoff to see if the reading is accurate. Given your driving habits, the blackout tape may be the best solution.