I put one in my '91 Civic. It's only 400 watts, but being right inside the block, it's pretty effective. I got it cheap on eBay. I think it was for an Accord, other than a very long cord, it fit fine. It won't get the engine up to full operating temperature, but it does get pretty warm. I can feel the heat as soon as I open the hood after having it plugged in for an hour or two. I've tried leaving it plugged in longer than two hours, but it doesn't seem to get any warmer beyond that.
I had always wondered why the coolant drain plug on the block was so big. One more reason to love Hondas!
