My MPGs are in the low twenties and I believe it's a combination of cold engine starts with a hilly and short commute to school and back everyday. I've thought about getting a magnetic engine block heater but I'm a skeptic and I would like to hear if anyone else has tried to get results using this method.
I don't use my A/C, let the engine warm up a little before putting it into gear, stock Mich tires @ 38 psi, mid to low grade octane (injector cleaning every 5th tank), royal purple recommended weight and a K&N filter.
I usually get 28mpg during the warm season and 38mpg on the hwy.

 

Someone on this forum once calculated out how much money it cost to run an engine block heater compared to the difference in cost for fuel for a warm/cold engine. It ended up being a wash, not counting the cost of the engine block heater (and installation). However, his variables may not match your own. There is an added benefit of more fluid oil with a warm engine being able to coat the metal parts quicker and limit wear. How much? May not make much of a difference for a 100,000 or 200,000 mile engine.

I've lived where the temps are easily in the single digits in the morning, with several mornings below zero. Even then, I never really warmed my car up much. Maybe idled for up to 60 seconds, then put it in gear and went easy on the throttle until the temp gauge came up above the C. Under those conditions, on my 3 mile each way commute, I was averaging 19 MPG. Now, with average morning temps around 35-40, and a commute of 1.3 miles each way, I'm seeing about 17 MPG. My car definitely doesn't get a chance to fully warm up by the time I get to work.

I just drove across the US, about 3,000 miles, while hauling over 1,200 pounds in my car (yeah, including my weight and a full tank of gas I was 360 pounds above max GVWR...). I averaged 70 MPH and got 35 MPG for the whole trip. With over 90K miles, I'm still getting pretty good mileage, when I'm not abusing my HAH with my awfully short commutes.

 

I asked a question somewhat like this awhile back but it was about a heater for the hybrid batterys. I still feel if those batteries were warm at take off the gas mileage would be better. Here in the midwest where it has been really cold this winter my mileage has been really horible this winter. When there were a few days when the temp. got over 30 I saw better mpg but when it was 20 and below I saw my mpg down around 23mpg. Most of my driving is highway and I still say this car would be a gas hog for city driving I wouldn't even have one, period.

 

I don't even think the IMA system will fully engage until the batteries are at a decent temperature ie.. you wont see and recharging while coasting until you warm up the pack a bit. For this reason I let my car sit and warm up for 5 mins if the temp is under 30…. I know its never good to idle but I'd rather my car last longer and put out less pollution as I drive it around.

You also might need to block off some cooling ducts around your grille as I hear that helps people in very cold climates. Just be careful not to block too many…..

 

Even around freezing temps, my braking regen starts happening by the time I hit my second stop sign. So, just over a mile and going about 25-35 MPH. I doubt the batteries have had any significant time to warm up by then. However, I may go over three miles before I see the Eco light come on.

 

Yes the battery pack has a separate heater(at least I believe it does on 05 models) in it which starts warming the tiny pack pretty quickly, then you get assist/charge as soon as the minimum temp is met.

 

Most of the HAH engine is Aluminum alloy which would make a magnetic block heater hard to use. Honda offers a bolt heater for the head closest to the front of the vehicle. Not sure how effective top down heating would be but it is what they sell.

My car needs to have the water temp at 167F as indicated by the SGII before it will indicate operation in ECO. This usually takes about 1.2 miles on relatively flat surface while driving using a very light throttle. Cooling system maintains 184-188F during normal operation.

 

I block my grill for as long as I can. Heats up much faster. I like Fords idea with the Focus, they use a curtain blind system. I hope that catches on with all manufacturers! H