I have a couple of questions for the technical experts on the forum but feel free to provide links to technical or service manuals that may answer my questions.

I have been doing a lot of reading here trying to determine how to maximize my mpg with my ’06 Prius. I have made several modifications to my driving habits as a result and I have increased my mpg by 2-3 mpg (over 5 tanks). My first question has to do with the 42 miles per hour threshold mentioned in many of the threads. Depending on my traffic situation, I will get orange arrows from the ICE to the drive train as early as 9 miles per hour and as late as 33 miles per hour. What is the difference in terms of impact on mpg when the ICE engages at these slower speeds rather than at 42 miles per hour?

Even when I keep my speed below 40 miles per hour for an entire trip, when I come to a stop I still feel the ICE shut down after a couple of seconds. Again, how does this differ from the actions of the ICE at and above 42 miles per hour?

As a corollary, what happens to the ICE after extended periods above 42 miles per hour (e.g. highway driving) and then dropping below 42 miles per hour? I don’t feel any noticeable change in the running of the engine when I drop below 42 miles per hour.

My second question has to do with the true value of a block heater in terms of increased mpg. How long does it take (in terms of minutes or miles) for the Prius to reach proper operating temperature? It seems to me the Prius reaches ideal operating temp within 2-5 miles of use. The reason I ask is, my initial trip in the morning covers about 30 miles and 30-35 minutes. After that, I am not in a position to utilize a block heater. Hence the only time the block heater would be used is for the first trip of the day and never after that. In addition, the Prius is in a garage overnight, where in the dead of winter (late December through early February) the outdoor low temperature rarely gets below 10 degrees (above zero). I am really trying to determine if the addition of a block heater (and its corresponding cost) will have sufficient impact (given its limited use) to pay for itself in enhanced mpg given the impact will only occur during the typical 2-5 mile warm up period at the beginning of the day.

Thanks for any feedback

UTpiper