Dear Tom and Ray:

Help! I have an '04 Chevy Trailblazer, and I live in the far north of Canada. It's minus 24 degrees as I write this. Can you tell me what the benefit is, to my engine, of using a block heater? -- Emily

TOM: Well, the primary benefit is that your car will start, Emily.

RAY: For those of you lucky enough not to live in the great frozen north, a block heater is an electric heating element that's installed in your engine block. You plug it in overnight with an extension cord, and it keeps the engine block, and the coolant inside of it, warm. And that, in turn, keeps the oil from thickening up.

TOM: When an engine gets bitterly cold, the oil gets thick, like molasses. If the moving parts of your engine have to push through this thick oil just to get started in the morning, they may not be able to do it. So the block heater keeps the coolant warm, and that, in turn, keeps the oil just warm enough so that it moves easily.

RAY: That has benefits for your engine as well. Most significantly, since the oil moves more easily, it circulates faster and gets to moving parts of the engine faster. So there's less time just after the engine starts when key metal parts are unprotected -- or underprotected -- by oil. That means your engine lasts longer.

TOM: The prewarmed coolant and oil also allow your engine to warm up faster and reach operating temperature sooner. That means you get less oil dilution from cold, unvaporized gasoline, and better fuel efficiency.

RAY: AND it means you get heat to your feet faster. When it's minus 24 degrees, don't tell me that the benefit of a warm passenger compartment isn't as important as any benefits to your engine, Emily!