Many drivers waste fuel by excessively idling their vehicles before takeoff.  This behavior is more pronounced during the winter, when the process often involves leaving unattended vehicles running to melt frost and “kickstart” the heat.  But in any weather and whether there is someone in the driver’s seat or not, long warm-ups are not recommended.  

I’ve referenced vehicle warm-up at least a few times in past columns.  It’s always been a sub-topic though, so I’ll give it a bit more attention here.  My opinion on the subject mirrors the popular consensus of vehicle manufacturers, certified mechanics, automotive engineers, hobbyists and driving enthusiasts.

A many of us already know, unattended running vehicles are forbidden in most jurisdictions, including Spokane.  The Washington law, RCW 41.61.600 reads (similar to Idaho’s 49-602 and other states’ statutes):  “No person driving or in charge of a motor vehicle shall permit it to stand unattended without first stopping the engine, locking the ignition, removing the key and effectively setting the brake thereon and, when standing upon any perceptible grade, turning the front wheels to the curb or side of the highway.” So, it’s illegal. 

Besides, the common wisdom of the above-named experts is that warm-up extended beyond 60 seconds is unnecessary and wasteful of fuel for any vehicle.  Instead, they collectively agree that 30-40 seconds of stationary warming before moving is adequate. There is also qualified, universal agreement that hard starts, hard stops, heavy throttle and higher engine RPMs should be avoided during the first few miles of driving, especially in colder weather. 

Depending on ambient climatic conditions, reaching full vehicle operating temperature (closed-loop, electronically) takes 15-20 minutes, at which time a vehicle is considered “fully warmed up.”  Driving the vehicle easily (after the initial less-than-a-minute of stationary warm up) is the most efficient way to reach that fully-warmed state. Drivers can minimize wear to vital mechanical parts by using gentle inputs to driving actions (starting, stopping, steering) and avoiding freeway speed until full operating temperature is reached.

Engine bearing clearances and other vital tolerances reach optimum measure when full operating heat is attained.  At that point, the engine’s coolant and engine oil reach a desired, stabilized temperature as well.  You will not likely experience immediate, noticeable harm by hard-running a cold engine, but you will induce added wear little by little, shortening the overall lifespan of its components. 

In a similar fashion, other moving parts and rotating shafts in the remainder of the drivetrain benefit from the full lubrication circulation and warm up achieved best via a few miles of relatively easy driving.  Brake systems work better after the first couple of pedal applications too — the machined surfaces of brake discs and drums regularly have a light rust coating from sitting that wears off quickly to allow even, predictable braking.  Tires even develop flat spots from sitting and may take a few miles to “round out” particularly in sub-freezing temperatures.

Older cars with carburetors were often warmed up longer to get the automatic choke to open and slow down the vehicle’s idle speed or to get it warmed enough to not die at the first few stop signs.  Since the proliferation of fuel injection (mid-1980s), those issues are not relevant.

When you’re ready to go, get in your vehicle, start the engine, apply seatbelt, check mirrors, adjust the seat — then get moving!

Readers may contact Bill Love via e-mail at precisiondriving@spokesman.com.

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