Block heater

Good advice above...and unless it's below 0 degrees, I don't ever use it.

Then only a couple of hours before start up.

The block heater is about 500 - 750 watts, and running all winter will add say $45 a month to your electric bill.

It only needs to run a couple of hours before starting it on a day that is below 32F. Most big rigs do not run then at all, and start up fine at 5F. Those in northern areas, might run a heater if they are parked overnight at below 25F for faster warmups, and to control oil pressure at start up.

If the engine is not warm and you run it near max RPM, it will be pumping a lot of very cold thick oil, leading to very high pressures. This is one of the reasons fire trucks are left plugged in 24/7 and so are hospital emergency generators, despite the electric costs.

Good luck,

Fred.

If you are talking about an hour or two before starting in low temperatures, YES.

If you are talking about leaving it on 24/7, NO. You would use a lot of electricity!

There are rumors that keeping the heater on speeds up oil oxidation, but Fire Departments have those heaters on 24/7/365 days a year with no ill effect.
But than if you don't plan to start the engine, than why?
Turn it on 2-3 hr before planning start.