Originally Posted By: MNgopher
Some block heaters have thermostats built into the cords - most of them do not allow the block heater to operate until the air temp is below zero.
Current F150's owners manuals state that the block heater achieves its maximum heating after three hours, and running it any longer is just a waste of electricity. Electrical usage is estimated at .4 to 1.0 kWh. At local electricity rates of 10 cents a kWh, plugging in the heater for three hours at maximum rates cost about 30 cents.
Maximum heat in 3 hours.
So what I infer from that is that it takes 3 hours before the block heater has heated up all it can and the engine is ready to start.
I live in Saskatchewan so it goes without saying I'm an expert when it comes to knowing cold,and the pros and cons of using a block heater.
I plug my cars/trucks in as soon as they are shut off,and unplug them once they start. Sometimes it's days before starting one or the other.
A timer is great it you are on a set schedule,but that's not me.
As far as block heater improving warm air getting to the occupant faster that's highly engine dependent.
Some block heaters are set into the block via a frieze plug and will heat up the area very well but it's not circulating.
The best type heaters I've found are a recirculating block heater. It has a pump which circulates heater coolant thru the engine and yes the heat will blow almost instantly. For 60 bucks I can get a 1500 watt type that starts the engine immediately.
My charger is strange. With the block heater plugged in not only does it warm the block but the oil and coolant are also heated and via the EVIC system at -35c my oil temps were 15c,coolant was higher at 60c.
So on that vehicle it's covering all the bases with its system.
My trucks and vans on the other hand aren't as sophisticated so I plumb in a recirculating type.
I leave them plugged in for weeks on end in the winter and last year because I almost never drove my truck it was plugged in pretty much the entire season.
So leave it plugged in if you like. It's not hurting anything.