Many drivers waste fuel by excessively warming their vehicles before takeoff.  Such actions are more common during the winter, when the process often involves unattended vehicles.  Still, in any weather and whether there is someone in the driver’s seat or not, long warm ups are not recommended.  

Reader S.R. sought advice on the topic as follows, “I love to drive and am always working on being a better, safer and more aware driver.  I am writing from work today because of an issue that keeps arising in my job. As [a public safety official], I work with hundreds of citizens and watch groups on crime prevention.  Recently we have had a few incidents where people have left their car idling in the morning to ‘warm it up.’  One with grave consequences and another, fortunately, only had items stolen, not the vehicle itself.  People often leave their cars idling, even if they are not warming them up.  That is another issue to be addressed.  Have you written a column on warming up vehicles?  The statement that I often hear is that the age of a vehicle will depend on whether it needs a warm-up or not.  To me there must be more to it than that.   I would appreciate a fresh look at the issue.”

Among hundreds of columns, over many years, I have referenced vehicle warm up at least a few times.  It’s always been a sub-topic within a column though, so I’ll give it a bit more attention here.  My opinion on the subject combines the popular thought of vehicle manufacturers, certified mechanics, hobbyists and driving enthusiasts.

First, as many likely 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. 

Aside from that, the common wisdom of the above-named experts is that warm up beyond 60 seconds is unnecessary and wasteful (of fuel) for any vehicle, and that 20-30 seconds of stationary warm up is adequate. There is also expert agreement that hard starts, hard stops, heavy throttle and higher engine RPMs should be avoided during the first few miles of driving.  That means if you live close to the freeway, rather than heading there directly, slower speed operation is advised for a few minutes.

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-60-second 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) until full operating temperature is achieved.

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 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.

Older cars with carburetors were often warmed up longer to get the automatic choke to open and slow down the vehicle’s idle speed. Since the popularization of fuel injection (mid-1980s), that issue is mute.

Start vehicle, apply seatbelt, check mirror and seat adjustment, and then get moving

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

---

---