[rs]

oops missed a bit. My car at the time was 2.5L and I noticed mpg going from around 30 to 40+ mpg.

It is very noticeable gently accelerating away from standstill, quickly getting into 5th (it was a manual). Also leaving air-con switched off added a few mpg.

Obviously it was much easier when everyone else on the road was doing the same thing.

[thorn]

I drive a Prius and when I really punch it the mpg goes down. It would help if every car had a mpg monitor like the hybrids do. People could see realtime feedback of their driving habits.

The best mpg I get is with longer trips, I recently drove 100 miles, mostly highway 65-70 mph with AC on and I was getting 54 mpg. Driving to work, 13-16 miles one way I get between 45-50 mpg. Colder weather hurts MPG also, takes longer to warm up. So far I'm ave about 47 mpg for the year.

I still see people driving like maniacs even w/ gas heading to $3/gal.

I read the best speed for the Prius is around 40mph. I guess It would depend on the transmission of the car what would be the optimal speed.

[pilferage]

$this->bbcode_second_pass_quote('thorn', 'I') read the best speed for the Prius is around 40mph. I guess It would depend on the transmission of the car what would be the optimal speed.

[BrownDog]

I have an air/fuel meter hooked up to one one of the stock o2 sensors, which shows a couple of interesting characteristics of the behavior of the computer. FWIWI, I have a fuel injected '94 Ford with EEC-IV and an auto trans, so some of this may be different with other vehicles.

The first thing of note is that after about 10-15 seconds of coasting, the mix goes completely lean, and doing research, I learned that the computer shuts of the fuel injectors when coasting in order to improve fuel economy. I can use this to my advantage when decelerating by not pushing the pedal at all. Even a little movement of the gas pedal will keep the injectors firing.

The other thing is that when I floor accelerator, the mix goes very rich. This is the WOT (wide open throttle) mode, which is built in for occasional high-power needs like passing, etc. Obviously, this will burn fuel much more quickly than in closed loop mode*, due in part to the richer mix. What I found surprising is how long it stays in closed loop before going into WOT. I can put the pedal about 80% to the floor and be accelerating fairly hard and still be in closed loop. I try to stay in closed loop to save fuel, and it seems to help.

*When in closed loop mode, the computer adjusts the fuel mix based on the o2 sensor, so the gauge bounces around what is called stoichiometric ratio (nominally 14.7:1 for gasoline/air). This is the supposed ideal mix for full combustion, set to improve fuel economy and also emissions.

One other thing to think about is that given the computer's preference for the stoichiometric ratio, the fuel use will be roughly proportionate to the engine RPMs. If you accelerate in a way that keeps the transmission in a higher gear (i.e. upshift sooner, avoid downshifts), the rpms will be lower and you'll use less fuel. If you drive an automatic, this will obviously mean not mashing the gas pedal so hard, but if you drive a manual shift, you can control this yourself.

Add these all together, and they support the idea that the way you drive probably will have an effect on fuel economy.

[kelee877]

I got my new car..ummm. i know but i live in the boonies..and need it..we have no buses that run on sundays and i know the bus runs by here evry hour on the hour at the 15,s...but..i have 4 kids and i have figured the costs..and well cheaper to have the car then run the transit..especially here...

[thorn]

$this->bbcode_second_pass_quote('pilferage', '')$this->bbcode_second_pass_quote('thorn', 'I') still see people driving like maniacs even w/ gas heading to $3/gal.

[thorn]

Prius Optimal MPG Table

Looks like 80F and 30 - 40 mph is the best for the Prius.

[JoeW]

I monitor my vehicle's fuel economy very carefully, and have been testing different driving habits to see their effect on mpg (results inconclusive).
No matter how I drive, my car ('99 Ford Escort 4-dr sedan/2.0L transverse 4-cyl sohc automatic transmission) gets about 30 or 31mpg. The low fuel light usually comes on around 290 or 300 miles on the trip odometer, and my fill-up is usually about ten gallons around 300-315 miles on the trip odometer.
With my most recent fill-up, I am now at 310 miles and my fuel gauge appears to have about 1/8 of a tank left. Assuming that the low fuel light comes on sometime during my next 25-mile trip, I will have gone perhaps 335 miles on 10 gallons, a feat that this car has never before accomplished.
Here's the really weird part...Since I am testing out different habits, I have been driving in a manner that I believed was less conservative, which I have done before, resulting in the same 30-31mpg I usually get.
I have not made any changes to the car, and I bought my gas at the same place I always go.
Could they be doing something to the gasoline to increase fuel economy? Has anyone else noticed a mysterious increase in fuel economy, or has my paranoia reached new heights?

JW

[strider3700]

Perhaps your guage is starting to go a little off, mine has been getting worse over the years. It shows almost full for the first 1/3 tank then moves normally until it hits 1/2 tank showing (maybe really only 1/3 in there) where it plummets to empty.

Anyways 1 tank doesn't mean much you'll need to get a relatively consistant increase to show anything is really improved.

My spreadsheet on gas doesn't show any unexplained improvement in mileage although my guage is tricking me into thinking it's great lately.

[nailud]

If I were you, I'd fill my tank ASAP. It's possible your fuel guage isn't as accurate as it used to be and you don't have as much left as you think you do.

[JoeW]

I will post the actual mpg calculated after I fill up later.

[rogerhb]

Or you are subconsiously driving more carefully?

The following all improve fuel efficiency:
1. Driving at an efficient cruising speed, typically 90kmh to 100kmh.
2. Accelerating smoothly rather than heavily.
3. Using the appropriate gears.
4. Not using air-conditioning (apparently this can save as much as 11% in fuel I was shocked to discover)
5. Changing your driving habits and not driving down to the corner store regularly.
6. Correct tyre pressure.

[adi]

Perhaps you're more concious of fuel efficiency now and drive better, thus preserving your fuel for longer?

[EddieB]

The AC is a big one. Also air temperature. Perhaps the air temp where you live has been optimal for this tank. I wouldn't put too much stock in a single tank of gas.

[JoeW]

Here are the results of last night's fill-up:
340 miles / 9.6 gallons
35.4 mpg

If the magic continues for the next tank, I will add it to this thread.
Again, I have been trying to drive like a jerk to see if it decreases my fuel economy, but instead I have seen the exact opposite...

[richardmmm]

could be the engine is getting a little older and more loosened up.

it sounds like something daft, but i experienced a considerable loss of gas milegage when I had a new engine put into an old pickup truck when the head gasket finally gave out.

think of it like an old pair of comfortable shoes. they are more worn in and so they need less energy to walk in.

it could also be some quirks in the timing and tuning of the engine an accidental glitch that teaked things up instead of down, it could also be the tires are more worn or less worn. It can also be summer to winter and altitude changes also cause gas mileage to change.

[sampo]

i've noticed the exact opposite thing in my last 4 fill-ups.
i've kept my mileage for the last 4 or 5 years by just writing the current miles on the trip odometer on the receipts for gas and then every few months grabbing the receipts and doing the calcs.
previously, i got an absolutely consistant 25-28 miles per gallon, with it never going below 25 no matter how much AC or how fast i went on the highway.

starting 4 fillups ago it goes like this: 23.3, 24.1, 22.7, 23.6.
after the first anomaly i checked the tires and had the air filter and oil and filter changed....
my tinfoil hat reaction has been that they are probably cutting the gas with some substitute!!!

[Nomoil]

It's not your fuel gauge. That has nothing to do with how many miles you get per gallon.
Have you considered tire pressure? Have you increased your tire pressure manually? Remember, temp. effects tire pressure as well. I forget what the numbers are exactly, but I think for every 10 degree increase, your tire pressure increases by a few psi.
Good luck.

[Specop_007]

Damn that evil cow. Damn her to Hell!



Click

May 24, 2006 -- WASHINGTON - In a surprise move yesterday, Sen. Hillary Rodham Clinton called for "most of the country" to return to a speed limit of 55 mph in an effort to slash fuel consumption.
"The 55-mile speed limit really does lower gas usage. And wherever it can be required, and the people will accept it, we ought to do it," Clinton said at the National Press Club.

Before sounding off on the benefits of a lower speed limit, Clinton called for a combination of tax incentives, the use of more ethanol-based fuel and a $50 billion fund for new energy research to cut the consumption of foreign oil 50 percent by 2025.

She also pushed for half of all the nation's gas stations to have ethanol pumps by 2015, and for every gas station to have them by 2025.

[Andy]

The 55 mph limit is probably the most sensible thing she has proposed in a while. Of course, there will be immense opposition but any peak oiler would know that measure could cut fuel use overnight by 5 - 10%. I maintain, if we want to travel quickly over land, we should do it on guided steel supports AKA railroads.