How do sub-zero temps affect car engines, batteries?

Experts at University of Michigan Ann Arbor weigh in on cold reality for cars

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ANN ARBOR – As we brace for a record-breaking cold front this week, University of Michigan professors are sharing their advice on how to prepare your vehicle for sub-zero temperatures.

Engines and batteries can become slower and damaged in extreme conditions, especially in electric vehicles.

"Batteries are weak when they are cold. They are like humans," professor of mechanical engineering and director of the U-M Energy Institute Anna Stefanopoulou wrote in a recent paper. "At cold temperatures, it is important to have plenty of energy left so you can start. Don't think that being near an outlet to charge will get you out of trouble.
 
"Our recent work shows that at low temperatures, you cannot charge, and it will be faster to discharge to warm up a bit the battery so your battery can safely accept the charging," she said. "So again, you need to leave plenty of charge to be able to start and go!" 
 
The extreme cold can also decrease the range of electric cars. 

"If you have an electric vehicle, or a cellphone for that matter, you have likely noticed the effects of the cold on your battery charge," professor of mechanical engineering Margaret Wooldridge said in a statement. "The colder temperatures reduce the time to discharge the battery, thus reducing the range of electric vehicles on a single charge.

"Diesel and gasoline engines produce a lot of waste heat which is used to heat the passenger compartment of vehicles in winter. EVs do not have comparable levels of waste heat, and have to use supplemental heating systems for the passenger compartments. This additional use of electric power with also lead to faster drain on batteries."

Andre Boehman, professor of mechanical engineering and director of University of Michigan's W.E. Lay Automotive Laboratory, explained how cars behave differently in extreme cold and what drivers can do about it.

"Engine coolant takes longer to heat up, which can mean that it takes longer for your vehicle's heater to start warming your car," Boehman said in a statement. "Fuel tanks or lines that are contaminated with water can result in fuel line icing that restricts flow to the engine. Diesel vehicles should be properly winterized. But when temperatures get extremely low, you run the risk of having the fuel form a wax, primarily from the 'paraffin' compounds in the fuel. This can clog your fuel filter and restrict flow to the engine.
 
"Because your lubricant needs to flow through many parts of the engine to allow the rotating and sliding metal components to slide more easily, cold lubricant may not flow as readily throughout the engine. This could lead to wear within the engine over a sufficient number of very cold starts, and is another reason to keep a block heater on your diesel engine."

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