Posted Wednesday, March 8/06 in Mods & Tests

Without trying too hard, you can probably think of a couple of reasons why it's better to drive a cold engine gently than to let a car sit idling to warm it up.

The obvious one is reduced fuel consumption. Another is lower emissions. And a big one is that driving the car actually gets everything up to operating temperature faster than just letting it sit running. (In fact, idling does nothing to warm the drivetrain, bearings, tires, etc.)

But how much faster? I didn't really know. Time to get some data!

The test:

This one's a really basic experiment: I timed how long my engine took to reach operating temperature (195 F) idling, from a cold start.

You're witnessing pure science here - I generally don't do cold starts since I installed my block heater, and even if I can't plug in, I never let the car sit idling.

(Have some fun here: before reading any further, take a guess how many minutes it took my car's 993cc powerhouse to reach operating temperature from a -7 C / 19 F start. Five minutes? Ten? More? Less? ...)

The test conditions:

• ambient: -7 C / 19 F
  
• cold soak (hadn't driven it since the day before)
  
• all electrical accessories off
  
• WAI in place
  
• didn't touch the accelerator at all - let the engine computer do its thing

The data:

The initialisms:

- FWT: coolant (water) temp in degrees F
- FIA: intake air temp in degrees F
- Lph: fuel consumption in liters per hour

Observations:

• How close was your guess??



• It was shockingly slow to warm up, wasn't it? 17 minutes! Way off my own guess. This is significant, given that this car takes about 4 to 5 minutes to approach operating temperature in similar conditions, when driven immediately from a cold start.
• The difference in cold fuel consumption is dramatic (from fuel enrichment and idle speed controlled by the engine computer). Immediately after start-up it was using three times as much fuel as when warm. On one very cold start this winter, I saw it at 2.0 liters per hour.
• The cold fuel consumption rate underscores the benefit of using a block heater. The one I installed raises the engine temperature by 35-40 F above ambient after an hour of plugging in, and 40-60 degrees if plugged in longer. That avoids the very worst of the cold-start LpH spike.
• It makes me aware of the fact that the block heater may be useful beyond typical "block heater weather" (below freezing). I may become a 3-seasons block heater user.
• Perhaps a bigger engine might warm up quicker than my 1.0L 3-cylinder mill, since it's generating more heat using more fuel (although it would also be a larger heat sink...)

In an attempt to educate the public about the various costs of idling, a number of jurisdictions have implemented public awareness campaigns - and even laws restricting idle time.

Resources:

- Yukon Anti-Idling campaign

- idlefree.ca - city of Vancouver, British Columbia

- Idle-Free zone - Natural Resources Canada

- In praise of the lowly block heater - MetroMPG.com

Post script:

I heard from fellow Metro owner Mark with a related Alberta winter tale:

" Excellent new article about the warm-up time. I actually guessed 20 minutes, but I had a little more information to go on than you did:

A few months ago during an especially cold day (-27°C / -16.6 F) I was stopped at a rather long light and eventually noticed that my temperature gauge actually started to drop. It was a noticeable drop and I rightly deduced that idling this vehicle on a cold day would do absolutely nothing to warm it up - especially with the heater [blower] on.

Unfortunately I simply can't plug it in every day due to parking conditions in my cul-de-sac, but after reading your info I can certainly see the benefit of doing so. Having a timer set to come on two hours before I leave for work would be a great thing."

-27 C: yikes! Fortunately, I think we're over the hump as far as this winter goes. Thanks, Mark!