Decent Highway Gas Mileage...
 

I think I got pretty good mileage on my 100+ mile trip from Colorado Springs back to Longmont.

http://i.imgur.com/B6UEG.jpg
45.9, got as high as 46.4 but the hills and stop lights kept running it down. Take off the 1-2 for the computer inaccuracies and its about 45 MPG.

This includes the several miles out to the high way with stop lights, climbing monument hill, a stop at Ikea, and several miles from the high way back home. Had the air conditioner on low for half the time and the head light on the other half.

This was to prove to a friend... "Its not what you drive, its how you drive it". Next trip will be back down at 30 mpg because its a hell of a lot more fun.

Whoa, going 45-55mph the whole time I assume? Takes some discipline to refuse to go faster than that in most cars haha.

Ha, that was 60-75, on roads with a speed limit varying from 55-75.

Its driving like my dad would, not fast not super slow...(in the slow lane with all the semis)

Damn you call that decent? Thats excellent mileage.

Wow that's actually really impressive. Maybe being in Colorado helps, theoretically holding 60mph at sea level will barely get you 45mpg or so. I think the air up there is like down 17% in density or something, that would be worth about 10% more fuel economy or so.

Could you see your reflection in the rear bumper of the 18 wheeler you were tailgating? ;)

(drafting can get you unreal mpg!)

Ive got a calculated 26+ mpg on my first few tanks in mixed driving. Then last tank I got 30! I haven't been afraid of revving it out either. Can't wait to see what it would do on the highway.

Dude you'd have to be drafting hardcore and going downhill the entire time to make this happen...

Sent from my Galaxy Nexus

You can't trust the mpg shown, since they tend to be off when calculating the average mpg (since they may not account for when the car idles, as it shows a blank "--.-" reading in those instances rather than 0 mpg, which is what is really what you get at that instant).

The best way to do it is to go by filling up the tank, driving, then calculating the mpg by taking the miles driven divided by the quantity of gas used to fill up the tank again. (It may not always be 100% accurate, but any variances will more or less get evened out.)

It's hard to tell, if the ECU could adjust perfectly it should be the same. Maybe the thinner air sits in a higher efficiency point of the FA20 for some reason. Would have to get a wide band o2 sensor to see if the ECU can get the AFR right.

The thinner air has less drag too, not that that is a big player on the twins cause of the .28 drag coefficient.

This is with a MT too, I wonder how well I could do with the AT gear ratio.

I would gladly trade whatever the high altitude affect is on MPG for the 34 HP it steals...:(

You're right, I had only used just over 2 gallons at this point and didn't want to refill up just to check MPG. The dash reading on mine has always been off +.5-2 MPG. (I still could tomorrow...)

Keep in mind the car may be more accurate than you think, gas stations are only legally required to be withing +/-10% on what they give you for gas. Since crooked corporations design the pump I would assume it always make it give you less gas than it says. There is no easy perfect way to measure MPG.

Toyota/Subaru have to be accounting for some of the idle time, because when you sit at a stop light, even though the dash says --.- MPG on the instantaneous screen, the average screen will decrease very slowly.

Sorry, but that's not true at all. That is a HUGE margin of error to begin with. And if that were really the case, people would notice with random tanks of gas being really terrible one week and really awesome another week but with the exact same driving patterns.

I actually have documented every tank of gas I've put into my car since I bought it, and I'd notice if there were something wrong.

The ECU does adjust. When the air is thinner, you lose power so you need a bigger throttle opening = less pumping loss. In a more abstract setting, having a lower starting pressure increases the maximum possible theoretical thermodynamic efficiency by increasing your "pressure ratio" although there's way too many things affected to say how this really affects the engine.

If the cruising power requirement were exactly the same you could expect maybe a couple percent efficiency increase. Since the air being thinner also reduces your aerodynamic drag (0.28 is pretty low for a production car but drag power is still pretty high at highway speeds) by 17%, your engine load just dropped like 9% (obviously depends on speed, which determines the ratio of aero drag to tire resistance). Since your thinner air is robbing more potential power from the engine than your cruising load has decreasing by, I think ~10% is probably a good estimate.

I remember some over sensationalist dateline stories about gas stations saying that it could be off by +/-10%, but after some random googling it looks like they are checked to ~0.5% every pump once a year. Looks like >90% of pumps are accurate when tested. So maybe .2 MPG variation...

1 internet point to you.

I have also wondered how accurate the pump auto click off point is, I have had random occasions where the pump would click off after 2 or 3 gallons even though I was on an empty tank.

~10% sounds reasonable.

A small part may be related to the fact the at altitude premium gas is lower octane, having a higher BTU per gallon. Of course most gas sold at higher elevation has 10% ethanol which would partly counteract this.

As far as I know trying to guess which fuel has more BTU per gallon is a total crapshoot, fuel varies so much and no oil companies are saying exactly what they're putting into the fuel.

45mpgs thats AMAZING, I barely get that number in my GOLF TDI (DIESEL)

How many miles since you cleared it? I can clear my average MPG and go down a hill for it to show 127MPG and take a picture of that...

Having said that, I have seen excellent mileage with this car. The best I've seen was 39MPG on the display (37.8MPG actual), which is still amazing. This was over the course of ~400 miles as well.

Right, though again, as long as you always fill up, it'll even out. I know what you mean though, but it's usually more of an issue if you fill up and don't need much gas, such as after driving 50 miles rather than going on a 300 mile trip (in which the gas pump shutting off too early or too late wouldn't skew your mpg too bad).

You just have to be consistent. Personally I fill up at the same gas station >95% of the time and do the same thing -- fill up, let it click off, then fill until it clicks off again.

It probably did help that Colorado Springs to Longmont is a ~1200 feet drop in elevation, but still, this is pretty dang good.

Very true. I have been averaging around 30mpg so far.

That's a significant drop. You should try the other direction too as a round trip route will produce more accurate results.

That would be great, but cannot take the MPG number unless you drive round trip. Isn't it EPA rated at 30 MPG highway?

Not all that accurate. They work by a diaphram and venturi effect. Basically if you look in the pump nozzle you will see a tube. The tube goes past a diaphram and back into the nozzle. As the fuel flows past the tube in the nozzle it creates a vacuum that pulls air into the tube (the Venturi effect) past the diaphram. When fuel reaches that tube then the vacuum is lost which causes the diaphram to move sutting off the pump.

Basically if you get the nozzle of the pump into the fuel filler hole slightly askew, where there is not a free flow into the gas tank, then gas will back up to the nozzle and cause it to shut off before the tank is full.

Lower Octane gas may or may not have a higher or lower BTU. While there is a relationship between BTU and Octane it only really applies to the pure forms of each different chemical, and is only a casual relationship not a correlation. Since Gasoline is a mixture of many types of Chemicals, two mixtures can have the same BTUs but different Octane ratings.

wow nice for a 10mi drive I did with cruise control set at 65 I get only 37

After a 180 mile trip, the average read 38.1mpg. Not bad for a sports car.

I have 6813 miles on mine. My overall avg is 33.8.

I've managed a calculated 42 MPG on an entire tank of gas several times this summer (not just 42 over a relatively short distance, but 42 for the entire tankfull). This was mostly highway driving, manual trans, with two adults packed for vacation.

I could have had better mileage if I babied it, but I wasn't driving for mileage necessarily.

Imperial (Canadian/British) or US gallons? Imperial gallons are a lot bigger and falsely inflate economy figures.

Yeah, a 42 mpg average in this car is a little bonkers when not even a Scion iQ gets that.

Well now, there is egg on my face. That's what I get for using some online calculator. You're absolutely correct, the math was way off.

725 km = 450.494 mi
48 L = 12.6803 US gal

450.494/12.6803 = 35.5271 mpg

Hey, 35.5 mpg is still pretty solid.

I recently refilled a tank on a road trip from WI to MI.

I got 36.37 mpg. with 91 octane fuel.

This was with stop and go traffic for 30 minutes in downtown Chicago.

I have a manual trans.