(Photo from cjander's thread: Block heater location)
Who's planning to use their factory-equipped block heater? It's beautiful and warm here in eastern Ontario today, but we'll be seeing some more single digit temps soon enough. We've already had one frost warning, and freezing temps aren't that far away.
For those not in the habit, why use a block heater?
1) You'll save fuel by reducing the "warm-up hit"
Your fuel economy sucks after a cold start.
The warm-up hit affects automatic cars more than manuals, because the transmission is programmed to hold lower gears longer until everything's up to temperature. (That's one reason why automatic fuel economy can be lower than a manual's in a head-to-head comparison.)
But manuals are also affected because regardless of transmission, the engine runs on an enriched fuel mixture until the coolant is up to a certain temperature.
And the colder it is outside, the longer it takes to get out of warm-up mode.
Also, oil viscosity (thickness) increases as temperature drops. The engine works harder and burns more fuel to pump it around and to move parts separated by an oil layer. (Does the Micra specify synthetic oil? If so, it's not as affected by this issue.)
2) You'll reduce wear
Most of your engine wear occurs from cold starts, when the oil has drained down into the pan. Warm oil will circulate through the engine faster and oil pressure will come up sooner.
It's also easier on the battery to start a pre-heated engine.
3) More comfy!
You'll get cabin heat sooner if you use the block heater.
Sure, you could also get heat sooner if you just idle your car in the driveway, but that just kills your fuel economy, increases emissions and costs more.
I've already started using the coolant heater in my old Firefly. I'm actually a "3-season" block heater user. It's not just for wintertime anymore!