How Long Should You Warm Up Your Car in Cold Weather?

For drivers who live where the temperature drops below freezing, winter mornings aren’t much fun. Even worse, their vehicles have to deal with the cold, too. Drivers want their cars to warm up fast so that they’ll run properly — and so the heater will hurry up and work.

But what’s the best way to warm up your car when it’s cold? A lot of people believe you should let your vehicle idle until it reaches normal operating temperature. Others are convinced that you should let your car idle very briefly, then put it in gear and let it warm up as you drive. The truth is, just a quick warmup is best, in most cases.

There’s no need to wait long — usually

Most experts agree: With modern cars, you don’t need to idle for a long period before you drive off in the cold weather. Technological advances like fuel injection and better motor oil mean you can hit the road quickly if you’ve got a vehicle made in the last 30 years or so.

Most car manufacturers recommend taking off after the engine has been running for 30 seconds. Then you should drive gently until your vehicle is fully warm. This actually warms up your car much faster than if you were just idling it while parked.

It’s also better for your fuel economy. Think about it — when your vehicle is stationary and idling, you are getting zero miles per gallon. That’s as bad as it gets! Plus, there are reasons why extended idling can actually be bad for your car, which we’ll get into later.

So, why do people say to let it idle?

The idle-until-it’s-fully-warmed-up belief is based in fact. The problem is, those facts are more than 30 years out of date.

Up until the 1980s, automotive technology was more primitive. This made extended periods of idling a necessity, and over time this practice became conventional wisdom. There were a couple reasons why this used to be needed — and why it still is if you drive a car from that era.

Carburetors: Back in the days before emissions controls and computerized fuel-injection systems, most vehicles had carburetors. These devices sat on top of the engine, vaporized the gasoline and mixed it with air. The mixture was then sent into the engine for combustion.

Because carburetors, with their metal components, were exposed atop the engines, fuel would not vaporize well at low temperatures. This resulted in rough idling, sputtering and even stalling. Warming up the engine for a while warmed up the carburetor, letting it vaporize the fuel better. This was the only safe option in those days, so everyone did it.

Motor oil: The oil used in vehicle engines back then was much less sophisticated than what we use today. Low temperatures in those days would thicken engine oil to a molasses-like consistency. The oil needed to get warm so that it could circulate better through the engine and provide lubrication to all the moving parts. An extended period of idling let the oil heat up, flow better and help the engine run more smoothly.

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Cars have evolved

In the 1980s, increasingly strict emissions standards rendered carburetors obsolete. They were replaced by much more precise fuel-injection systems. This created a big change in the way engines operate — and how we get them started in cold weather.

Today’s fuel-injection systems are computer-controlled. They are able to recognize cold weather and compensate for it by providing a richer fuel mixture. The computer can also monitor the engine’s temperature as it warms up and adjust the mixture to suit. A high-pressure fuel pump guarantees the proper vaporization of the fuel. The cold-weather starting process is now much more reliable, with minimal time needed for engine components to warm up before being driven.

The quality of the motor oil in your engine has improved since the ’80s, too. The demands of increased fuel economy have resulted in thinner grades of oil. These not only reduce friction for better mileage, but also flow much better at low temperatures. In fact, the latest fully synthetic oils are able to flow easily at temperatures as low as minus-40 degrees Fahrenheit.

Why idling can be a bad thing

Despite these advances, the notion of idling to warm up your car has stuck around. The truth is, it’s almost never necessary these days. In fact, there are several downsides to prolonged periods of idling:

• It lets the richer gasoline mixture strip the oil from the engine’s cylinder walls, increasing engine wear
• A rich mixture from a cold engine can damage your catalytic converter
• Your vehicle pollutes a lot more when idling in cold weather
• Long periods of idling are illegal in most places and could get you fined
• Fuel consumption increases, so you’re wasting gas
• Idling is the slowest way to warm up your engine and your oil

But notice that we said “almost never.” We admit there are a couple situations where it’s a good idea.

When idling may be necessary

It’s a big country, and winter means different things in different places. Many of you may experience mild winters, where the temperatures don’t get too far below freezing and there isn’t a lot of snow or ice. But for folks living in the northernmost latitudes, winter means long stretches of subzero temperatures and major snowfalls.

If you deal with very extreme weather, you may need to idle for longer periods of time, especially if your car is covered with snow or ice in the morning. Issues of safety and comfort come into play here. You’ll need to remove the ice and snow from your vehicle before you drive away. You’ll also want to be sure that your windows will stay clear once you’re driving. And you want to get your heater is cranking.

For these reasons, a longer period of idling will provide you with safer driving conditions. Simply start your car and take a few minutes to clean it off, if necessary.

Use common sense and stay safe

For most of us, most of the time, there’s no need to let the car idle for long in order to warm up. Whatever type of winter weather you have, use the appropriate technique for your conditions, and put safety first.