AB sells a genuine LR block heater that lists for around $150. I've just installed a Phillips from O'Reilly (part no. 3100039) that was $22 and is built a little better. For those of you reading this and living in hospitable climes despite the subject line: It's a small electric heater which fits inside the block through a freeze plug opening. You pry out the freeze plug, insert the block heater which has a 110V power cord, and after refilling you can plug it into a wall outlet to keep the engine warm when it's waaaaay too cold out.