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Temperature & Fuel Economy While a car’s straight-line performance can increase with colder temperatures (denser air means more oxygen, which means more “boom” in the cylinder!), most cars start to suffer in fuel economy when the temperature drops significantly. This drop in economy is due in part to the factory tuning of most vehicles, which tend to run a rich air-to-fuel ratio until the cylinder walls are warmed up to aid in fuel ignition. Unfortunately, most cars only go by a designated coolant temperature, and if the car never gets up to optimal running temperature, the tune stays richer than needed (because the cylinder walls are now hot but the car doesn’t know it) and more unnecessary fuel is burned. Have you ever seen those 18-wheels roll around with the front grill near-fully covered? That’s to limit the cold air from over-cooling the coolant so that the vehicle can stay at optimum temperature. This can work on normal cars as well, and sometimes with something as simple as a piece of cardboard.
We’ll discuss some specific components in detail, but here’s how it stacks up: When the temperature drops from 23°F to -4°F, fuel efficiency drops by 10%. And when the temp is below freezing, fuel economy can decrease by up to 20% on any trip under 4 miles.
(De)Ice – While it’s certainly more comfortable to drink your coffee inside the house while your vehicle warms up and self-defrosts, that’s a whole lot of time with MPG at 0. Do your wallet and the environment a favor – use an ice scraper and deicer. (Just don’t pour hot water on your windshield as nicks and fractures can crack!)
Batteries – It goes without saying, cold weather is hard on batteries. Every electrical component in use places an additional strain on your battery. As your alternator works overtime to keep the battery charged, fuel efficiency is affected. By not using electrical components (such as fans, defrosters, wiper blades and that beloved seat warmer) longer than necessary, you’ll decrease the load on your battery and increase fuel economy.
Give that battery a helping hand by keeping the top clean. Dirt serves as a conductor, draining battery power, and corrosion serves as an insulator, inhibiting flow.
Antifreeze – If you live in an area where extreme cold is common during the winter, and the car spends a lot of time parked outside, chances are you’re running a lot of anti-freeze in your cooling system. And if you’re not, you should be. Sufficient anti-freeze prevents the engine block from freezing up (totally frozen water expands and will crack your block), and it prevents freezing in the radiator as well - which would otherwise hinder the flow of coolant to your engine and cause it to overheat.
Tires – Tire pressure tanks by 1 PSI for every 10 degree drop in temperature. When tire pressure decreases, rolling resistance increases, reducing fuel economy. Your monthly tire pressure check should be upgraded to a weekly task during cold weather.
Consider a seasonal tire swap, even in warmer climates – summer tires begin experiencing faulty performance when temps fall below 45°. Even a thin layer of ice can weaken summer tires, resulting in poor handling and braking.
Oil – Engine oil thickens as temperatures drop, creating friction between moving parts in the engine and transmission, reducing fuel economy. Use a low viscosity in winter, as recommended by your owner’s manual.
Warm-up time on cold mornings kills fuel economy, but so does driving a vehicle before its reach its optimum operating temperature. So where’s the balance? Give your vehicle that initial warm-up time and many of its systems will thank you. However, idling for too long creates build-up on spark plugs, so experts recommend keeping that warm-up to just a few minutes.