I put this together, in hopes it will answer a few questions for some. Block Heater FAQ
How much power does the heater draw?
About 7-10 amps.
What size extension cord do I need?
A 14 gauge extension cord will work for 25-30' run. If you are going to run 50' or so, its a good idea to step up to a 12 gauge extension cord.
Can I leave my truck plugged in all night?
Yes, many people do, but if it is not super cold in your area, 3-4 hours before start-up works very well.
Can I just use a timer?
Yes, I use a 15 amp timer (10amp should works just fine too) and I set it for 2 hours before I leave.
When do I need to use my block heater?
Anytime really. Here where I live it only gets down to maybe 40°F at night. But I like having the truck warm up a lot faster when I start it. Also a warm start-up is better on the engine.
Do I have to use the block heater?
No. The Duramax is capable of starting up even in pretty cold climates without being plugged in. In cold climates, it will take quite some time to warm up however.
I cant hear my block heater, is it working?
The block heater is simply an element (kind of like a probe) in the coolant stream in the block. When plugged in, power flows thru it and causes the element to get hot. This heats (or warms) the coolant in the block. You wont hear anything really, the same as you dont hear power running thru the power cord itself
Does the block heater automatically turn on and off?
Some trucks have a thermo-plug. It only allows current to flow when it is below zero. Look at teh end of the plug on your block heater, does it look like a normal plug, then it probably is. Does it look squarish, and look like there is extra plastic, and bigger than say a normal extension cord plug? If so, it most likely is a thermo-plug. (You can actually cut it off an replace with a normal plug avail at a hardware store)
Where is my block heater plug?
Its on the passenger side, tapped up or zip tied in some factory loom, running down from the passenger side battery to the frame rail. If you find it, and then cut back some of the tape and loom, you can gain an extra foot of length or so, and it will reach further. If you leave it taped up like factory, you will notice it doesnt reach very far.
Do I have a Block Heater?
Yes, All Duramaxs have one, I if you think you dont, you need to keep looking, its there...