The temp dropped about 25 degrees over the last week or so and my FE has gone down with it. When it was 95 degrees I was getting 54.4 MPG during my daily commute. Now that it's in the upper 60's to low 70's my MPG has gone down to 47.3 while my route and driving techniques have remained the same. One thing I notice is the engine seems to need to rev more to produce the same power. I was easily able to keep the revs under 2k when it was hot out. Now it seems the engine jumps to 2,500 rpm and up to produce the same acceleration now that it's much cooler. I'm surprised at the difference. Wonder if the FE will worsen as the temps continue to drop. Hope when the temps are in the 30's my MPG aren't in the 30's as well.

"Quit jackin' with my MPG!"

Darn right my friend. You FE will sink as the temperatures drop.

Now, the best relief for good FE in cold temps is to install and use a block heater. Plug the car to a timed outlet every night and it takes a couple of hours of power to reduce/remove the high RPMS at startup.

The other thing that helps FE - especially in snow and ice conditions is winter tires. Good winter tires in ugly lightweitght steel rims, that is .

Also, attempt some cold-start-Pulse&Glide techniques and that should help too.

Cheers;

MSantos

I see the same thing on my 05 Civic. After speed, wind, and wet/dry condition of road surface, it seems like air temperature is the next most important factor influencing gas consumption.

We need input from a Honda engine design person on this topic... couldn't the heat produced by the engine be used to warm up whatever it is that needs to be hotter, so as to further increase efficency?

Yes, it would be nice but then each company has their own rules concerning release of un-sanctioned technical information to the public domain.

However, in regards to your closing question:

The heat produced by the engine does make its way to the components likely to be affected by lower temperatures. The IPU module (behind the rear seat) is designed to operate normally as long as the temperatures allow. As long as it isnot too cold and not too hot, its protection subsystems will not impede its contributions (IMA regen and assist).

The heat makes it way there because the air cabin is used to condition the IPU. The designers assumed that Mr. Freeze would not be driving the car in the winter, nor would Lava girl be driving it in the summer.

But, the worst hit to the FE in the winter months comes from the engine attempting to warm up to an optimal temperature that contributes to maximum operating efficiency. One of the best things we can do to help the engine achieve this goal faster is to use a block heater (as mentioned above and often on this forum).

Cheers;

MSantos