Should you warm your car up in the winter before driving? I spoke with more than 30 mechanics and couldn't get a straight answer.

• Car manufacturers don't have consistent advice on how long you should idle your car in the cold.
• So it's no wonder mechanics don't all agree on the subject, either.
• Generally speaking, idling your car for about 30 seconds when it's cold can help it run smoothly.

It's cold outside and you're running late. Is it OK to just start your car and go, or should you wait for the engine to warm up a bit before hitting the road?

This winter, I've often found myself in this predicament and it's made me wonder whether my impatience — and poor time management — is taking a toll on my car, or the environment.

So, I did what anyone might do: I called my mechanic. Then for good measure, I called a second mechanic. To my surprise, they had completely different pieces of advice.

One said to idle the car for three to five minutes before driving while the other said I didn't need to wait at all. I called a third mechanic to settle the matter, but he merely told me something entirely different, which was to wait 30-60 seconds.

At that point, I was on a mission. I called half a dozen mechanics across half a dozen states for some semblance of clarity. I got recommendations that ranged from 0 seconds to 10 minutes.

Why all the confusion?

It's no wonder there's confusion. But, let me first say it's not because of the common myth: that cars before the 1980s ran on carburetors, which had to be warmed up for several minutes in the cold or they would stall out, and therefore modern engines need the same (they don't).

It's true carburetor engines and the cold don't get along, but it's not why the more than 30 mechanics I spoke with couldn't agree on how long I should warm up my 2013 Honda Civic. They obviously knew my Honda doesn't have a carburetor.

The confusion falls somewhat on car manufacturers.

In a report from Oak Ridge National Laboratory, researchers compiled idling recommendations from owner's manuals across various makes including Ford, Chevrolet, Honda, BMW, Lincoln, and many more.

Some manufacturers lacked any advice on idling time — my Honda's owner's manual falls into this category. Others like Ford and Chevrolet recommended idling for no more than 30 seconds after starting.

Whereas Infinity and Nissan advised idling for at least 30 seconds. And Toyota suggested idling for "some dozens of seconds" — whatever that means.

So, how long you should idle your car in the cold seems to depend on the make of your vehicle. But if you're like me, and your owner's manual lacks any advice, here is a good rule of thumb.

A good rule of thumb that takes the environment into account: about 30 seconds

Despite the debate about whether optimal idling time is more, less, or around 30 seconds — that 30 seconds seems to be a good rule of thumb to follow for most drivers on cold days.

This is because the motor oil in your car drains to the engine's bottom after the car's been sitting for more than several hours. When you start the ignition, the oil moves through the engine lubricating the pistons, cylinders, and other moving parts. On a warm, sunny day, that process happens almost instantaneously, but when it's cold out, the oil moves slightly slower, and therefore needs a little more time.

How much time is where mechanics diverge on the subject, but around 30 seconds is the general consensus for modern engines. On extremely cold days you may need about a minute, but no more. Why a few mechanics told me this process takes five to 10 minutes, I do not know.

What I can say is if you idle much longer than 30-60 seconds, you're just wasting gas and money. For every two minutes you spend idling, you lose one mile in gas mileage, which, depending on car type and fuel prices, can cost anywhere from tens to hundreds of dollars a year on wasted gas.

Idling also doesn't properly charge the car battery, and can shorten battery life. Moreover, it contaminates your motor oil, the Oak Ridge report pointed out, leading to more oil changes than you'd otherwise need.

And last but not least, you're unnecessarily polluting the environment.

"You have more emissions when the engine is idling rather than when it's driving," which is worse for the environment and why over half of US states have laws against idling, said Bassem Ramadan, department head and professor of Mechanical Engineering at Kettering University. 

What mechanics agree on: don't floor it right away

Whether they tell you to idle for 10 seconds or 10 minutes, every mechanic agrees that you should not floor the accelerator when you first start driving in the cold.

The cold causes metal in your engine to contract, which leaves tiny gaps between the moving parts that can strain it, said Phil Carpenter, director of operations at Urban Autocare and Avalon Motorsports in Colorado.

"Everything in an engine has tight tolerances," Carpenter said. After the car warms up, "all the metal expands, and things start to fit back to the way they're supposed to actually fit."

Gunning your engine already strains it even when everything is running smoothly. When you gun it and those gaps are there, it's a lot worse, Carpenter said. "That's when your turbo can fail in that 60-to-90-thousand-mile range. It's not a guarantee … but the likelihood is higher."

Ramadan said, depending on weather conditions, it can take around five minutes after you start driving to get a car up to temperature. If you idle the car instead, it'll take longer.

This is also why, even for people who defend long idle times to warm their cabins for comfort and defrost their windshields, it's unequivocally better to drive than to idle because your car will warm up much faster when it's moving.

Yes, you'll be cold for those first few minutes and you may need to drive slowly around the block a couple of times before getting on a main road to give your defroster time to heat up.

But at the end of the day, you'll save some money and help the environment.