Q: Where is the outdoor temperature sensor on a car generally located? I ask because the temperature indicated on the dashboard doesn't always agree with the figures I see posted elsewhere, like on my phone's weather app. If the sensor is located under the hood, would the heat reflected from the hood elevate the true indicated temperature?
A: The outside air temperature sensor generally is behind the front bumper, so the engine heat has no influence. Nonetheless, the readings can be affected by the heat of the pavement, especially on a hot summer day. You also might notice that the temperature changes slowly. That is to prevent wild swings as you drive.
Jake brakes and noise
Q: What are jake brakes? Why are they so loud? And can anything be done to eliminate the noise?
A: Short question, but longer answer. Developed by Jacobs Vehicle Systems, jake brakes use the engine to slow down a truck. In simple terms, they expel air via the exhaust valves before the compression stroke ends, siphoning off some of the energy that normally would be directed through the cylinder to the drivetrain. As for the sound, which is made by the escaping air, it's similar to that of, say, a trombone as vibrating air pulses out of the bell end.
Jake brakes can't stop a truck, but they do allow a driver to slow down with less use of the service brakes. The only option for reducing the noise is to ban their use. That's why, in populated areas, you'll see signs saying "Engine braking prohibited."
Kid at heart
Q: I recently bought a Dodge Challenger with a hemi and manual six-speed transmission. (Yes, we're talking about a midlife crisis.) I expected to have a brake dust problem, but one has never materialized. Can you explain why?
A: The friction compound on brake pads is a lot like brownie mix. They contain differing ingredients. Some brownies are chewier than others. Some brakes are dirtier than others.
Q: I read with heightened interest the letter about keyless ignitions allowing drivers to forget the engine is running. The letter writer has a GM car and can lock it while it is still running. My wife has a 2014 BMW X3 SUV. I have a 2018 Audi A4 sedan. Neither will allow this to happen. If we try to lock either of our cars while it is running, the car will stop as soon as we press the "Lock" button on our remote.
A: The system you mention is a step up, but it still is possible for you to leave your car running in your garage if you don't lock the doors. Toyota is equipping some of its vehicles with an automatic shutoff feature that will turn off the engine after a predetermined period. And phone apps are in the works. But technology is not a substitute for paying attention while operating a vehicle.
Bob Weber is a writer, mechanic and ASE-certified Master Automobile Technician. His writing has appeared in automotive trade publications, Consumer Guide and Consumers Digest. Send automotive questions along with name and town to firstname.lastname@example.org.