Thought I would post my experience with installing the block heater. Perhaps it will add something to the knowledge base for future reference. Quite a bit has been mentioned above and I will try not to restate what has been said.
Ordered the factory block heater from:
http://www.handa-accessories.com/insight.html~$40 USD plus freight. Found good service there, as I had to talk to them about the freight. Installed per the included directions and also checking with the service manual on refilling the coolant system. The plug in the back of the block was a bit of a struggle, but it finally gave way, and although I had borrowed a clean shallow mop pan from wifee to catch the coolant from underneath the car, more than I would have liked managed to miss the pan. A 15/16 socket works just fine in place of the 24mm for tightening the block heater. Since this socket was in the 1/2inch drive set, the 1/2inch ratchet or break-over bar works great for removing the existing drain plug from the block. It was a little hard to read the torque wrench when installing the heater, but a strategically placed mirror might have been helpful.
Refilling the coolant ( per the service manual on page 10-12.) was the most consuming part of this installation. I used a short piece, ~6 inches of 3/8inch id clear vinyl hose and just happened to find a funnel (on hand) with a small enough spout to fit inside the tubing. The OD of the tubing was just right to use the clamp that came off the factory cap, to keep the tubing tight on the steel tubing coming up from the engine. The clear tubing makes it easy to see the bubbles coming up and the coolant going down. It took quite awhile for the temp to get high enough for the radiator fans to come on, and I did have to throttle up to ~2000RPM and hold for a bit to get it done. Gave the hoses some squeezing (personal preference, not by the book) to help burp the air pockets (caution here as the top hose gets pretty warm before finished, and the bottom hose is in close proximity to a rotating pulley). As things get warmed up and most of the air is purged, the coolant will begin to backflow from the funnel. Removed the funnel and vinyl hose, (lost a little more coolant here), and installed the factory rubber cap/clamp and tightened the bleed fitting again just to make sure. Manual said to let the fans cycle twice, three times is that much better, right :?:. Didn’t plug the heater in as I wanted to drive the car to make sure everything was normal. All went well on a round trip commute last night. I did catch the dash bars up to 8 one time while doing the bleeding/burping routine, but only up to the normal 6 on the commute. Checked the reservoir after returning home and added the rest of the quart of coolant left from the install. The radiator showed full after removing a_COOLED_cap.
I should have bought a quart (or more) of coolant before I started, because I spilled so much during the install that I didn’t want to start the engine until I had coolant on hand to replace what had been lost. One quart appears to have done the trick, but since the Insight only holds ~2.6 US quarts I could have done the coolant change while I was at it, although I only have ~50k on the car. The local dealer charged me only $4.08 USD for a qt., which I didn’t think was too bad.
Tips for the next guy:
1.After removing the factory block plug and letting the coolant drain into the pan borrowed from wifee, move the pan before trying to install the heater, unless you periodically wash your sockets in coolant. (Don’t ask me how I know

)
2.This coolant is sticky and messy when it gets on your hands. When using digital camera borrowed from wifee, you will probably need to wash your hands_AND_ clean up the camera often. (See parenthetical remarks in tip #1)
3.Do this where you can wash the coolant off any painted surfaces.
4.Keep an eye out for curious pets. Coolant is potentially fatal for them if ingested.
Wanted to get his done in preparation for working on my engine blanket:
http://www.insightcentral.net/forum/viewtopic.php?t=3916
Just sharing my experience-no liability expressed or implied :lol:
Randall