Hi,
I found you all in the process of researching a block heater for a Cat 3126.
There is a rear THREADED plug on that engine. HotStart has an expense heater that fits that plug and probably others have heaters. Search for "TL101-000" and you can find an installation sheet. Surely a threaded bushing could be inserted into the original plug female fitting and other generic and cheaper heaters could be installed.
Of all the solutions, this strikes me as being the safest and most fool proof. It should eliminate chances of coolant leakage and fire. I would much prefer to plug this heating element and forget it than fret over other methods. Removing a freeze plug in an installed engine might be a recipe for leakage.
