It's been getting in the 20's lately and my truck runs like complete crap and smokes like a building is on fire for the first minute of running in 20 degree weather.

My block heater never worked. Ohm tested the cord where it plugs into an electrical outlet, nothing.

Today I tried to remove the block heater cord from the block heater via the knurled nut. First I tried by hand, and got a diesel blister. Then I tried plyers, then I tried vice grips, then I tried bigger vice grips and... OH it moved! Now it moves back and forth about 1/16". So I put a light on it and sure enough THE WHOLE BLOCK HEATER IS MOVING!!!

Why can't I take the cord off the block heater? I was told it is removed by hand. Why is this so hard?

 

Its probably rotted in there. Best to drain the coolant and replace the heater with another one. Theyre not terribly expensive and they dont usually pop.
I think its just threaded into one of the freeze plugs with a bracket slipped in behind the block.

 

Your block heater may be ok.
It's quite common for the wires to break close to the AC plug,
Cut off a couple inches behind the plug then measure resistance.
If you get almost a complete short just replace the male plug end.

 

Ok, I cut the male end off of my cord, checked resistance between what was left of my block heater cord and there still was no continuity. I also checked the plug end I cut off and it had no continuity also.

So I have to check my block heater element for continuity, but I can't because I still can't separate my cord from the element. Any ideas?

 

You're sort of stuck.
The way the block heater tightens in requires the cord be removed.
The heater has an allan head bolt in the center that makes it expand when tightened.
You're going to have to figure a way to keep the cord from spinning while untightening the knurled nut or somehow cut the cord away to expose the allan head.
Or maybe some penitrating oil will free it up. Use the real stuff, not WD40, etc.

 

The cord is seized to the block heater. No human will be able to remove it.

I went out and bought a 12ft piece of heat tape/pipe heater and wrapped it around the lower radiator hose. It's got to be better than nothing