[8307c4]

These pre-heaters are only used in very cold climates when an engine gives such problems starting it in winter I mean the engine won't even turn over, it is that cold.

How do I know, I spent a couple of years in the Rocky Mountains, I won't quite laugh off the New England winter but I can almost guarantee it isn't that cold.
I never plugged mine in unless temperatures fell into the single digits or below.
Windchill doesn't count, straight up single digit Fahrenheit.

The short of it being, you probably don't need an engine block heater, unless...
With a good, fully charged battery, the engine fails to even crank, maybe then.

Because $80 cost of hardware aside I know you will pay more in electricity to pre-heat the engine than fuel it will save, we're talking about spreading warmth in a badly insulated environment that is full of air leaks, the slightest breeze goes right through that engine bay, you couldn't keep it warm unless you dropped a flame thrower under the hood.
Do NOT wrap the engine in a blanket!!!
That is a fire hazard, and the reason I mention it is because I had thought of doing it.

For that reason, for a pre-heater to be effective it needs to stay plugged in overnight, these heaters don't take a completely cold engine and warm it up, there simply isn't enough power in them, not even the most powerful ones (which burn, as one might imply, a certain amount of kilowatt / hour).

The way these things operate is ....
As SOON as the car is parked and the engine is off, you plug it in and leave it plugged in overnight and hope it keeps some kind of meek temperature in the oil.
The engine will still be cold in the morning, one hopes it's not quite as cold.
Oh, we're looking at running a tiny space heater outside in the parking lot for 8-12 hours.

Best kind to get, unless you want to spend hours installing one and since heat rises is a magnetic kind that you can pop onto the bottom of the oil pan, for a more permanent installation you can usually attach it to one or two oil pan bolts with a bracket.
Then run the electric wire through the grill and attach it there some kind of way with a cable tie or tie it up in a loose knot, make sure the electric cable isn't in the way of any moving parts such as fans or pulleys.
Or if you don't bolt it on just pull it off in the morning, might want to wear gloves, the mating surface still does get quite hot.

You may not think so, but doing it any other way is a complete waste of time.