Running the heater makes a car MORE efficient

Okay, here’s some nitpicking. Running the heater will help cool the engine so it will actually improve gas mileage slightly.

A link to the Staff Report is appreciated. Does using your car radio reduce your gas mileage? (Staff Report by SDStaff Dogster)

And just what is it that you can cite that says which engines run more efficiently at .5 degrees farenheit cooler when the heater is running (along with the blower motor, which is powered by the alternator, which requires energy, which comes from fuel)?

If you are going to nitpick, expect to be broadly picked.

A. Does running the heater reduce engine temp?
b. If so, it is measurable?
c. If measurable, does that reduced engine temp result in better mileage?
d. Is that lower engine temp coming at the cost of running the blower motor, which would offset efficiency or decrease it beyond the savings?

Philster wrote:

In a '67 Mustang, in the middle of summer, in stop-and-go traffic, it’s very much measurable. Turning the heater on saved me from overheating on several occasions. You could watch the temperature guage go back down over the course of just a few minutes.

But Hail Ants’ point is far too broad to cover just that situation. There comes a point where being too cool costs in efficiency, such as having one’s oil at a higher viscosity, thus increasing the drag on the engine parts themselves.

A friend of mine was into dune buggies built from VWs, and he was told to wire all the cooling wide open, permanently. He found it made a frothy mess of his oil, so it really didn’t flow too well. Don’t know what kind of effect that had on his mileage, but he figured it wasn’t doing the engine any good.

When the thermostat on my Mustang stuck closed (overheated in spite of heater being on full-blast), a gearhead buddy of mine told me that removing it without replacing it was nothing but a bad idea. If cooler was always better, there’d be no thermostats at all.

“My dream is of a day where every SDMB poster will have a quote of mine in their sig.” - Arnold Winkelried


If we’re talking pure Otto heat-cycle efficiency then cooler does run more efficient.

Real-world, however, cars are tuned to run at a certain temperature vs fuel/air mixture. It is mechanical limitations based on the engine’s design that limit the “theoretical” efficiency that could be reached by operating at lower temperatures. An engine could easily be designed and built that would run in Antarctica with a higher miles-per-gallon than your Honda Civic, but the market for sub-zero temp economy commuter cars isn’t very large…

I don’t know about gas mileage, but I used to have this rust bucket of a Ford truck called a Courier, years back, with a MAZADA II engine in it (Ford! Made in America. Riiight.) that over heated if I went too slow, like in heavy traffic. So, I’d flip on the heater and not only roast myself out (no A/C), but I’d actually managed to keep the engine from over heating.

I can’t remember whether it was my Fiero or my Camaro, but I had a car that had coolant and air passing through the core all the time. You would divert the air into the passenger compartment if you wanted heat.

Turning on the heater in this care did nothing, since the engine was cooled either way.