My Pontiac Firefly / Chevrolet Metro / Geo Metro / Suzuki Swift welcomes fuel efficiency nerds everywhere

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Latest fuel economy stats
for my '98 Firefly 1.0L 5-speed
  best: 2.3 125.1 104.2
 worst: 6.4  44.1  36.8
prev.3: 3.3  82.3  68.6
   all: 3.8  73.4  61.1
L/100km | mpg IMP | mpg US
Jul 28/07: more, graph, calc.
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Best non-hybrid MPG: Mitsubishi Mirage
Highest MPG for a new car: Mitsubishi Mirage?
Mitsubishi's 1.2L, 3-cylinder Mirage is the first new non-hybrid car that can match an old Metro's mileage. The company says 44 mpg (US) highway, 37 city. (Some drivers are already beating that in various economy driving contests.) How? An efficient engine, very light weight and aerodynamic design.

Cheapest to own? 2015 Nissan Micra Forum
2015 Nissan Micra Forum
The Micra's fuel economy isn't its most notable feature -- the $10,000 price is. That makes it one of the cheapest cars to own. And its 109hp, 1.6L engine and good power-to-weight ratio means it's fun to drive too.

Latest 10 posts:
1. Recipe for getting 99.7 mpg from a Geo Metro
2. - famous aerodynamic Honda Civic gets a web site
3. Snapshot: effect of tire pressure on rolling resistance
4. 65+ vehicle modifications for better MPG
5. Metro mania: forget stocks, put your money in old Geos!
6. 100+ Hypermiling / ecodriving tips for better gas mileage
7. Experiment: how long should a block heater be plugged in?
8. Everything old is new again: Car and Driver magazine modifies an econobox to improve MPG
9. Project Convertible XFi: alfresco efficiency
10. The floor is yours: MetroMPG opens a fuel efficiency forum
11 ... 64. Show all posts

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Good MPG forums: I spend a lot of time at and have also been known to lurk around

Chevrolet Aveo forum - discussion of the Chevrolet Aveo and its siblings (Pontiac Wave, Pontiac G3, Suzuki Swift+, Daewoo Kalos).

> Lots more Metro links...
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Send me a note:
darin AT metrompg D-O-T com,
or here

MetroMPG has opened a fuel economy forum
Read about the project here, or go straight to
ScanGauge fuel economy computer Save fuel with a ScanGauge II fuel economy computer.
I personally recommend this tool. I've owned both versions (I and II) and can't say enough good things about it. If you're serious about saving fuel, get one.

For more information and to order, visit EcoModder.

Experiment: how long should a block heater be plugged in?

Posted Thursday, April 17/08 in Mods & Tests

block heater plug

OK, so spring may not the best time to be talking about block heaters. Then again, the planet has two hemispheres, after all. So while it may be finally warming up here, somewhere somebody may be plugging in a block heater right now...

Plus, who says block heaters are only for sub-zero use? I use mine three seasons of the year. (And the only reason I don't use it regularly in the summer is because I'm lazy.) Toyota's hybrids (like the Prius) employ their thermos-like tanks to preserve coolant heat for efficiency gains whether January or July.

The question this post addresses is: how long should you plug in a block heater? In other words, what's the shortest time needed for the maximum temperature rise?


  • Why use a block heater?
  • Test details: two block heater styles tested
  • 300 watt warm-up time
  • 800 watt warm-up time
  • Combined 300w + 800w warm-up time
  • Observations

Why use a block heater?

I've written about block heaters before, so I won't go into much detail. From an efficiency standpoint, the big reason is because engines use less fuel when they're fully warmed up - as demonstrated in the cold start idling warm up experiment. In addition to efficiency benefits, they also decrease cold start engine wear and deliver heat to the cabin sooner.

Test details: two block heater styles tested...

The purpose of the test was simple: to measure the amount of time it takes to warm up the Firefly's 1.0L / 993cc engine from a cold soak (over night) condition with two different block heaters, separately and then combined. The block heaters in question are:

  • A 300 watt external bolt-on element style heater. This is the OEM block heater available for this engine. I installed it in December, 2005.
  • An 800 watt inline tank style coolant heater. I installed one in April 2007 because I wanted faster warm-up and higher temperatures than I was getting from the OEM unit. It's mounted inline the heater core return hose and uses convective circulation.

Both heaters use standard (North American) household power, 120 volts.

Temperature readings were taken from a ScanGauge every 15 minutes.

Note: the engine was started and idled for 30 seconds every 15 minutes to mix and circulate the coolant past the temperature sensor to get an accurate reading. This was necessary with the 800w inline heater due to "localized" (uneven) heating of the coolant. Both "pre" and "post" idling temperature readings are noted on the graph. The same method was used for the 300w heater measurements, even though there was negligible difference between the before/after idling temperatures with that heater.

300 watt warm-up time...

300 watt graph

800 watt warm-up time...

800 watt graph

1100 watt warm-up time (300w + 800w heaters running simultaneously)...

1100 watt graph


  • Regardless of the wattage, about 75 minutes appears to be about the time the temperature rise starts leveling off, give or take 15 minutes.
  • Anything beyond 2 hours is a waste of power.
  • With the 1100w combination, 84% of the total potential warm-up occurs in 45 minutes, 93% in 60 minutes.
  • The ideal plug-in time will vary between vehicles depending on the mass & heat dissipating properties of different size engines. This data may translate to other small engines, but anecdotally, I've read that 2.5 to 3.5 hours are required for a 3.3L V6 engine to reach a stable temperature with a 400 watt heater.
  • Of course the only way to know for sure what's best for your engine size & block heater power is to try it yourself!

Resources ...

EcoModder fuel economy forum Note: MetroMPG has opened a fuel economy forum
Read about the project here, or go straight to

darin AT metrompg D-O-T com, or here