Idling Your Car...Good Idea or Bad Idea?

Jesse Fulbright, MSU Liberty County Extension

I entered into an interesting conversation yesterday with someone at church about whether it was necessary to warm your vehicle up or not in the cold weather.  While I find it nice to get into a warmer car in the cold months of the year, the question that I really have to ask myself and perhaps you need to ask too is, “Is it helping the engine in my car?”  The answer is, probably not.

The basis for this thinking extends to when car engines relied on carburetors.  Before 1980, carburetors were the heart that kept car engines pumping.  Therefore, if your gasoline was too cold, your car wouldn't run rich, it would simply stall out.  In those days, it was important to get the carburetor warm before driving.  From the 1980s on, however, electronic fuel injection took over and is still what powers today's car engines.  The key difference is that fuel injection comes with a sensor that feeds the cylinders the right air-fuel mixture to generate a combustion event.  Does this happen right away?  Not exactly.  As I said, engines with fuel injection have sensors that compensate for the cold by pumping more gasoline into the mixture.  The engine continues to run rich in this way until it heats up to about 40 degrees.  By idling for longer periods of times you're putting extra fuel into the combustion chamber to make it burn and some of it can get onto the cylinder walls according to the experts.  Gas can wash oil off the walls if you run it in those cold idle conditions for an extended period of time 

Driving your car 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 generated by the radiator will flow into the cabin after a few minutes, idling does surprisingly little to warm the actual engine.

Both the EPA and energy.gov say a car should not idle for more than 30 seconds at a time.  Not only is it more environmentally friendly, but also cost-effective.  Idling for 30 seconds uses more fuel than restarting the car. 

Photo courtesy of Country Living

Of course, hopping into your car and gunning it will put unnecessary strain on your engine.  It takes 5 to 15 minutes for your engine to warm up while driving, so take it nice and easy for the first part of your drive.

So, my advice for myself and everyone is to put on those gloves, take a minute to scrape the frost off the windows and take a few extra minutes to drive at a prudent speed to your destination.