The long-held idea that you should let your vehicle idle in the cold is only right for carbureted engines.
In the thick of winter, the common thinking is that when you are gearing up to take your truck out in the cold and snow, you should step outside, start up your engine, and let it idle to warm up. But contrary to popular belief, this does not increase the life of your engine; in fact, it reduces it by stripping oil away from the engine’s cylinders and pistons.
In summary, an internal combustion engine works by using pistons to compress a mixture of air and vaporized fuel within a cylinder. The compressed mixture is then ignited to produce a combustion event—a little controlled explosion that powers the engine.
When your engine gets cold, the gasoline is less likely to evaporate and produce the correct ratio of air and vaporized fuel for combustion. Engines with electronic fuel injection have sensors that compensate for the cold by pumping more gasoline into the mixture. The engine goes on to run rich in this way until it heats up to about 40 degrees Fahrenheit.
“That’s a problem since you’re actually putting extra fuel into the combustion chamber to make it burn and some of it can get onto the cylinder walls,” Stephen Ciatti, a mechanical engineer who specializes in combustion engines at the Argonne National Laboratory, told Business Insider. “Gasoline is an outstanding solvent and it can actually wash oil off the walls if you let it run in those cold idle conditions for an extended period of time.”
The life of parts like piston rings and cylinder liners can be greatly reduced by gasoline washing away the lubricating oil, not to mention the extra fuel that is used while the engine runs rich. Driving your vehicle is the fastest way to warm the engine up to 40 degrees so it switches back to a normal fuel to air ratio. Even though warm air produced by the radiator will flow into the cabin after a few minutes, idling does surprisingly little to warm the actual engine. The best thing to do is start the vehicle, take a minute to knock the ice off your windows, and get going.
Of course, hopping into your vehicle and gunning it straightaway will put unnecessary strain on your engine. It takes 5 to 15 minutes for your engine to warm up, so take it nice and easy for the first part of your drive.
Warming up your vehicle before driving is a leftover practice from a time when carbureted engines dominated the roads. Carburetors mix gasoline and air to make vaporized fuel to run an engine, but they don’t have sensors that tweak the amount of gasoline when it’s cold out. As a result, you have to allow older cars warm up before driving or they will stall out. But it’s been about 30 years since carbureted engines were common in vehicles.
So unless you’re rolling in a 1970s Chevelle—which we assume isn’t your daily driver—bundle up, get into that cold vehicle, and get it moving.