Lost 6mpg

[Evil D]

So i took some advice and changed my driving habits....shifting at a lower RPM (i don't have a tach, i shift at 10/20/30) and coasting to a stop instead of down shifting. Well, i lost 6mpg on this tank vs. the last one where i didn't do any of that. This to me makes no sense at all, so am i missing something or can 6mpg be blamed on hotter weather? I don't know if it's really been that much hotter, at least not enough to justify that much loss. Another thing is this tank had no highway miles at all....do these cars actually get better mpg on the highway even with 12s going 65mph? If so then that's another surprise because i figured with such small tires and going 65 that it might not get as good mpg on highways.

[crazyrog17]

the gears are set up to handle the small tires on the freeway. they'll just spin 'em faster and you'll still be getting more mpgs because you're travelling farther with fewer RPMs.

harsh starts are where the gas is dumped out the tail pipe. you might feel like a jerk to the people behind you, but take off a little slower from the lights/stopsigns.

[doylerl]

As far as highway miles, it should get better. If you figure around town, say you get stopped at say 5 stoplights, even though you are not moving, your car is still running, burning fuel and giving you no mileage in return. This may have something to do with it.

[Pu241]

Never had a festiva get better city MPG than highway, no matter what wheels/tires I have on it.
Don't think hotter weather would reduce your MPG, unless you have the AC on.
I know colder temps will reduce MPG.
Just a few thoughts:
Your refill might not have been accurate. This last fill up, you might have filled it up more than previously. With the hotter weather the gas volatilizes more and burps the tank, permitting you to put more gas in than your "normal" fill-up.
I suspect this is only part of the issue, the other being highway vs city. With a 400+ mile highway drive I can get 45-48 MPG at 60-65 MPH.
Also check your tire pressure.
Remember, anytime your idling the engine you are getting zero MPG, and you have to get pretty high MPG to offset that. Cruising at highway speeds you have no idling time to overcome.
Larger tires to a limit, will increase your MPG, provided you correct your ODO/speedo for the larger tires, a GPS unit does nicely.

[Evil D]

Really the only variable between these last 2 tanks where my driving habits unless weather played a part. I guess it must be the lack of highway miles.

[festyxfi]

These little cars definantly get better mpgs on freeway trips...sometimes quite a bit more. If I'm only doing town stuff (which is rare) 40 might be it. Long freeway trips get closer to 50mpg.

FX

[FB71]

high temps will negatively affect mileage also, but not that much by itself. I suspect, as above, the lack of hwy travel was the major contributor.

[TominMO]

ALL cars get better mileage on the hwy. A lot of the issue is not slowing down and then having to speed up.

To compare city driving to hwy driving is apples to oranges. Even with extreme hypermiling in street driving, I could "only" get 50.5 MPG city. On the hwy, at a steady 60 MPH I got 52.5. At 55 MPH I got 58.5 MPG, due to lower RPMs and lower wind resistance.

Then there are the other issues, like:
the condition of your engine, regarding tune, the oil you use, and wear;
the size, width, and air pressure of your tires;
the condition of your bearings and brakes (i.e. not dragging);
ambient air temp;
gasoline quality.

[xaero_81]

I thought that the hotter the temp (to a point) would get you better fuel mileage because the engine has to generate more of a spark in cold weather to combust.

[TominMO]

I thought that the hotter the temp (to a point) would get you better fuel mileage because the engine has to generate more of a spark in cold weather to combust.

I don't think the ignition has the capability to generate more or less of a spark depending on air temp. Motors actually work better with colder air (again, up to a point). But that is somewhat offset by the fact that the colder, denser air is harder to push through aerodynamically. So overall, I suspect that this is one of the smaller considerations in gas mileage.

[FB71]

correct. The ignition has nothing to with it. Air and fuel temps are the major factors. In very cold weather, fuel will condensate inside the combustion chamber. Liquid fuel will not burn, only fuel vapor. Warmer air and fuel promote vaporisation. But, excessively hot air gets thin, and less oxygen is present in the cylinder, resulting in less combustion pressure. This requires greater throttle angle, resulting in lower economy.

[FB71]

ALL cars get better mileage on the hwy.

Not hybrids! :p

They do better in city driving because they are using the electric motor and regen braking, where on the highway, the gas engine is running constantly.

[TominMO]

Not hybrids! :p

They do better in city driving because they are using the electric motor and regen braking, where on the highway, the gas engine is running constantly.

OK, Mr. smartypants....

[batstiva]

FWIW, the 2010 Prius literature says it gets 51 city/ 48 highway. Not much of a difference, IMHO. That's according to EPA test results.

To the OP, maybe we are just doing it wrong. Seems like every time I make an effort at semi-hyper mile tactics, my results end up being no better or worse than if I just drive the way I drive, and check the results at fill up. :dontknow:

[TominMO]

FWIW, the 2010 Prius literature says it gets 51 city/ 48 highway. Not much of a difference, IMHO. That's according to EPA test results.

To the OP, maybe we are just doing it wrong. Seems like every time I make an effort at semi-hyper mile tactics, my results end up being no better or worse than if I just drive the way I drive, and check the results at fill up. :dontknow:

One of the new technologies supposedly coming out is shutoff at no throttle--like when you are at a light. Then pressing the gas pedal re-starts the car. Saves you from wearing out the ignition by using the key to shut it off at the red light, which is one of the hypermiling techniques. Another is to slow down as you approach a red light, because sometimes it will turn green before you get there, and you won't have to accelerate from a stop; you might be able to cruise thru the intersection still doing 20 or 30 MPH. Along with coasting whenever possible, avoiding braking, and accelerating moderately.