Finally started using my block heater, which I was able to install several months (?) ago by switching to an RSX Type S water pump housing and water pump, which also includes an oil -> water heat exchanger. For those that don't want to dig earlier in the thread, the Insight block heater fits into the K series coolant drain hole, but there's a hole in the side of it where an optional water passage runs to a heat exchanger that sits between the oil filter and the block. Without closing that hole somehow, water would just gush out of the block with the block heater in place. The RSX oil warmer serves this purpose nicely.
Right now it's early Autumn and we're seeing a lot of 50's-60's F afternoons and 40's F mornings, and I'm finding that 30 minutes of block heating in this weather is worth very roughly 5mpg on my morning commute, or approximately 45mpg -> 50mpg, give or take. I plan to collect more data.
Running it costs ~6.4 cents per hour. At $2.70 per gallon (for premium fuel, which I prefer for the extra torque and improved economy from E0), 45mpg on my 12 mile commute to work uses 72 cents of fuel, and 50mpg reduces that to 65 cents. Or, in other words, 3.2 cents worth of electricity saves me ~7.2 cents of fuel. I expect most of the savings are in the first 90 seconds of driving, where the engine would otherwise run more rich, though I can probably tune out most of the startup fuel enrichment.
