262.2 miles and I filled it with 11.848 gallons. It works out to around 22mpg. That was using 93 gas. This is sooooo bad. That was with mostly city driving but not hard driving. What should I do.

Dustin

 

my p5 with 2600 miles on is giving me no more than 260 miles before "empty gas tank" light comes on.
My MPG are around 21-23 mpg in all city driving, kinda sucks.

 

whats with this. some people are gettin really good mpg while some get shi$tty mpg. The car is rated at 25city 31highway with 5spd which is what i have. Why am I gettin such bad mpg.

Dustin

 

I have yet to take a close look at my all in-city driving mileage as it usually gets corrupted by a highway run here or there, but when I do drive only in the city it does seem to go through gas a bit quicker that I would have expected. However, the run that it makes is a really short one from home to work and the car might not get the chance to really get up to it's full operating temp for most of the drive. In addition, a lot of that time is spent stopped at traffic lights... no mileage going on, but a lot of time passing.

I dunno.... how are the EPA city numbers come by? is it really just driving at a lower speend and not accounting for any stop and go?

 

OK... I answered my own question at the following site:

http://www.fueleconomy.gov/feg/info.shtml#estimates

from that site:

it appears that they test the cars for some pretty run of the mill weather. I am not sure, but I would say that whilst my car is warming up in cold weather it is going to be burning a bit more fuel that if it were wearming up from 68 F. Of interest will be to see what the numbers do for the car once the warmer climate arrives.

Also of note for highway they never run over 60mph.

Of course then there is this little statement, that might just blow anything I said out of the water:

Anyways... it is an interesting read none the less.

 

I'd have to say STOP BUYING CHEAP(SHITTY) GAS. Don't get gas from places like Arco, 76 and some other ones. Not that 87 octane gas is bad, just dont buy it from bad places. Those places buy the gas from bigger companies like Cheveron for cheap because cheveron or some other company can't use it because it doesnt meet their standards. So pay the extra 25cents and get the good stuff hehe

 

Yeah, there are way too many different driving conditions, so i'm not surprised that people are getting 5 MPG differences. And from the site JJB mentioned, the way they determined the highway MPG is by driving no more than 60 mph on a highway!!! come on guys, I'm pretty sure you guys don't drive slower than 70 mph on highways (a modest guess) Running at higher RPMs will obviously consume more gas.

 

The way you match or better EPA estimates is by driving smoothly, and shifting early and staying in as high a gear as the engine will tolerate.

Note that this doesn't mean slow acceleration. Your engine is most efficient when running at about 80% load. So, by accelerating moderately hard in each gear, but shifting early and getting up to cruising speed rapidly and then into top gear will result in the best economy. BMW demonstated this in the '80's, possibly as an explanation to justify its Eta series, but it did show that full-throttle acceleration to get up to speed and then running in the tallest gear was much more efficient than slow acceleration and/or running in lower gears. (Gas engines are very inefficient at low loads.)

Running around in a lower gear at high revs will use more gas than running ar lower revs and higher load. The P5 can be put into 5th as low as 30 mph, but 35 mph is probably a better speed. So, when you are cruising around in traffic, you just put it into top gear. If you're cruising around in 2nd or 3rd at those speeds, you're just wasting gas.

My '98 Accord (4-cyl, 5-spd) is EPA rated 25/31. If I can keep it under 70, I can match or beat the highway numbers, but I have averaged 28.8 mpg during the last 3+ years/46k miles. The worst tank was 25.4 mpg.

My '90 Protege LX hasn't been doing that well lately (22-25mpg), but it's an autocross-only car (2000 miles, 7 races and 4 practices with 2 drivers in 5+ months) that carries 2 people and 200+ lbs of stuff in it when not racing. Although I did average about 30 mpg (with one tank at 38 mpg driving around Yellowstone) on my summer vacation/racing trip (over 3800 miles).

My new car ('02 Altima 3.5SE 5-spd) is too new to tell, but my trip computer says I'm getting about 26 mpg so far in about 50% stop and go driving. But then again, I haven't gotten on it much yet as it's still new.

 

Davard, you brought up a couple of points I was gonna mention plus more.

I agree about cruising with the top gear. More bang for the buck. Less rpm for higher speeds.

I haven't worked out my rpm for cruising at certain speeds (on relatively flat terrain of course, as different slope grades will affect the rpm required to maintain a certain speed), and what the best speed to cruise at is. My theory is, the faster you get to a location, the less time you spend using gas, the less gas you use. e.g. If i am driving 40km/h, my rpms are around 1800rpm. If I am driving slight above 60km/h (about 62??), my rpm is about 1800 rpm again. I need a bit more gas to get to 62 of course, but if I get there fast enuf and spend more time cruising, I will save gas. (btw, I drive an auto if these numbers seem weird.)

In that example, I am in different gears of course to be cruising at those speeds. What I want to figure out is what the optimal cruising speed is on highways, as I will be in the same gear from about 60km/h and up.
e.g. 120km/h is 1.33 times faster than 90km/h. But will I be using 1.33 times the amount or more gas than at 90km/h? That would depend if the rpms will be 1.33 times or more I believe.

btw, in reply to other posts, a decrease in fuel economy could be due to the longer warmup (and even for those who don't warm up, idle is higher when you are in gear w/a cold engine compared to a warm engine, for autos at least). I noticed a fuel economy drop when I got a nail in my tire, which caused my tires to be underinflated.

 

Hey, just to poke a couple holes in your theory.
you're theory about getting there faster hence less time on the road is a little incorrect. By that logic the faster you go the less energy you use, hence if you get where you are going in an instant you use no energy. I don't think that holds true. What you are missing is that your engine is spinning faster and more gas is being pumped in by the injectors.

Unfortunately as your car speeds up, things like wind friction against the skin of your car increases, rolling resistance increases, drag increases. You must use extra gas to fight all these. Eventually you're car will reach a terminal velocity dictated by the power of your engine. This is why the US likes the 55 mph limit cause it saves gas. The slower you go the more gas you save (to a point) The question is, what is more important to you, the money or the time you will save by going faster.

Stocker
Cheers

 

That's what I said. I haven't checked the ratio of rpm to speed in my top gear yet. I'm sure it's not a linear curve, so there's gotta be a sweet spot somewhere.. =).

 

FWIW, you save gas by getting to your cruising speed faster than accelerating slowly. Less revs will use less gas in this technique.

The optimal cruise speed for fuel economy depends a lot on gearing, as well as drag coefficient, tires, etc. On cars that are geared taller, the speed is generally higher than for car that are geared short.

For example, my '90 Pro LX is turning 1500 at 30 mph. Optimal speed for fuel economy seems to be 40-45 mph (2000-2250 rpm). Any slower and you are too far down the torque curve in high gear, requiring proportionately larger throttle openings and consuming more fuel.

With a car that is geared tall, the optimal speed is a likely higher. My mother had an '85 Buick Century with 3.8L V-6. At 55 mph (1400 rpm) cruise speed, it got about 26 mpg. At 70 mph (1800 rpm) it got nearly 30 mpg. My Protege gets about 35/30 mpg at those speeds (2800/3500 rpm). Bumping it up to 80 mph (4000 rpm) and the mpg drops to about 27 mpg.

 

I disagree with this. I have done many accelerating mass problems. (Turbines, motors etc) Accelerating a large mass quickly always takes more energy than accelerating it slowly. Not to mention the reduction in stress on your car by accelerating slowly.

Stocker

 

I think slope grades will not affect engine rpm at a given speed due to fixed gearing. Say 4000rpm at 80mph in 5th. That is constant. The engine just needs more gas to maintain that rpm when going uphill. Am I making sense?

 

We got 34mpg on the way back from Erie (350miles)