wow, picked up 2mpg out of nowhere
 

just filled up the Cavy tonight, 11.554gallons, 335.9 miles 29.08 MPG!!!

the car normally averages low to mid 27s with 26s when i goof around

i didn't do anything special, or different then usual, that i know of, tracey thinks it may be because we didn't use the heat as much this time...i don't see how that can make a huge improvement, we don't usually use it a whole lot anyways to begin with

the only thing that makes sense to me, is possibly the computer learned the additional airflow from the ram-air & K&N filter...possibly

Well, FE economy is just one of those things. I mean, look at my fuel log, it can be all over. Perhaps you're just more unconscious of ecodriving, :)

i dunno man, all i know is that i hope it continues this 29mpg streak ;)

I don't know if this has anything to do with it, but in Maryland it has been raining a bit recently. I have noticed a slight gain in mileage while it is raining compared to when it is dry.

You'll know on the next tank. ;)

the only part of useing the heat that would affect your gas mileage is the blower fan, a vehicles heat comes from waste heat from the engine, and that is "free" altho running the blower fan puts an electrical load on the engine, not a great big one, but enough of a load that it can affect engine idle speed.

Until the engine is fully warmed up, running the heat will hurt your mileage. Cold engine = less mpg. Running the heater will slow the warming process, so more time is spent with the engine cold. Even having the temp set to heat, without any fan, will take some heat from the cooling system.

"Even having the temp set to heat, without any fan, will take some heat from the cooling system."

I've been told it's not enough to matter. There will be a small amount of heat exchange but I'd wager it's peanuts, unless maybe in something like a Metro 3-banger that has a hard time heating up anyway.

I'd have to agree with you both. During warm up, I think its beneficial to not run heat to get the fastest warm up. However, once it is warmed up I see no problem with blasting as much heat into the cabin as you want. I don't think you'll see much of a decrease in effeciency as the engine is already producing tons of excess heat.

... or a 4-banger civic with aluminum block. With a complete grille block and the heater temp set to Cold, it takes all of my 11-mile commute to get up to temperature. It's 10-20 degrees colder if I have it set to heat, even with the fan off. Fan on, even colder.