Gotta go have another look at my '06 LX's owner manual for the gas tank size. 13.9? I am interested in seeing how accurate the gas gauge is, and tracking my gas usage more carefully. How many bars equal a gallon? And does it change as you go down? Getting @ 30 (not complaining) in a mix of city driving with and without the a.c. (have had the car for little more than a week). Waiting for a long highway trip to see if it gets close to the claimed 40. My '91 Accord got a pretty consistent 34 on the highway. The new car should do better; 1.8 vs 2.2 engine size, couple hundred pounds lighter, rpm at 72mph 23-2400 (auto) vs 2800 on the Accord (manual). We shall see. But it is still green, just ticked over 1000mi on the odo.

 

You can't really rely on the accuracy of the gas gauge to determine fuel economy. They're never that accurate. They can give you a "general indication" of how you're doing on a given tank by noting how far you get before the first light drops off, how many miles you've achieved when you get to half a tank, etc. Beyond that, the only way to know for sure is to top off the tank, reset the trip meter and drive. When you fill up again, top the tank again and divide the number of miles driven by the number of gallons consumed. That'll give you your fuel consumption. If you really want to be **** about it, always fill up at the same station and pump. That way the car will always be sitting at the same angle and you'll be reasonably assured that you're filling the car up to the same point.

I have always found that from time to time, I'll get one tank that does exceptionally well or one that is pretty bad on the mileage numbers. I tend to discount these, especially if I'm filling up at a station that I'm don't normally use, because I can't be sure that I getting a typical top off of the tank. Averaging out the mileage numbers should give you a better idea of how you're doing over the long haul.

FWIW!

Drive Safe,
Steve R.

 

Here's the best--most accurate--method to measure your fuel efficiency:


1. The best way to accurately measure Miles Per Gallon (MPG) is to fill your tank to the first auto-off click at the pump, then reset your trip odometer to zero. Now go drive. Next time you stop to fuel up, fill your tank to the first click, then write down how much fuel that was (or just get an automatic reciept). Now write down the mileage on your trip odometer. Then divide that mileage by the amount of fuel you put in your tank, and you've got a fairly accurate idea of your MPG. To make this more accurate, try to fill up at the same pump each time and reset your trip odometer before you restart your car. (This all sounds simple, I know, but so many people go by the "tank of gas" method that I thought this was worth re-explaining). If you really want to be accurate, do it at the same time of day when the temperature is the same.

2. Now why is this all important. Yes, yes, it's good for the planet, and that's fine. But it's also good for your wallet--an immediate payback, especially now. For example, I currently own two vehicles:

My Ford Explorer: 400 miles takes 20 gallons of gas. Gas costs $3.10 a gallon. To drive 400 miles thus costs me $62. This is about 15.5 cents/mile. (This is all easy arithmetic--just divide and conquer).

My Honda Civic: 400 miles takes 10 gallons of gas. Gas costs $3.10 a gallon. To drive 400 miles thus costs me $31. This is about 7.25 cents/mile. I now have $31 I can use to buy a case of beer and two packs of Marlboros (or put into my child's college fund, or contribute to the American Cancer Society, or use to buy groceries, etc.).

Clearly, this will add up over the course of the year--it costs half as much to drive the Honda as it does to drive the Ford Exploder, so, if all you need is transportation from Point A to Point B, there is no reason to drive the SUV. If there is some functionality that the SUV provides that the Civic does not, you then have to perform a Cost/Benefit Analysis to see if that functionality is worth the extra cost.

You can get even more deeply into this, by figuring in the cost of the vehicle and so on. You can even figure out the Total Ownership Cost (TOC), manufacturing to disposal, taxes, tags, license, insurance, maintainance, repairs, tires, and so if you want to take the time, and get a real view of what this all costs. Or you can go to Yahoo Autos and they have a neat tool to figure this all out automatically (it appears to be pretty accurate).

Monitoring fuel mileage is also a great diagnostic tool. If your MPG suddenly drops, you know it's time to start figuring out why.....

Hope this helps.

I'm expecting to do the Interstate no AC windows down run this week, despite temperatures being 100+ degrees! Wish me luck!

 

Agreed, although as I was reading this, I was thinking, "only if you fill up at the same pump and station," and then you added that! I hadn't thought of the temperature part. I'm sure it's a factor but I'm not sure it's that big of one on a tank by tank basis but it you "really" want to be **** about it, it's something to keep in mind.

I do tend to top off the tank when I fill up. I know, I know, I'm not supposed to do that but I've found that I can get another 2 gallons in the car after that first auto-off click. On my Civic, that's another 60+ miles down the road. It probably does throw my averages a little but I think that part will cancel itself out over time. So far, I've filled the car two times since the original tank of fuel it came with. I got 31.9 on the first tank and 31.7 on the second. Looks pretty consistant to me, so far, and I'm not going to worry about a stray tenth here and there.

FWIW!

Drive Safe,
Steve R.

 

first tank on an ex for me was 35 went down to 33 when i was using ac non stop as it has been near 100 several days its supposed to be 102 here tomorrow. 2.85 i get cheap gas. compared to everywhere else

 

I'm thinking that there must be an SAE standard for gasoline loading pressure-activated back-check valves that are utilized at all gas stations, just as there is for the neck of the car gas tank and the nozzle of the pump, across the country. Maybe it's not as iffy as it seems...!

I think wild variations in temperature may make some difference--if I'm not mistaken gas comes out of the underground tank somewhere around 57 degrees F. If your car has been parked in the sun, the gas in the tank might be 120+, and thus occupy more volume in the tank. Hmmm. Any ideas?

"I'm not ****, I'm just an engineer!"
--An Anonymous Roman Road Builder, 178 B.C.

 

Maybe, but I'm not convinced of that. I've seen significant differences in fill pressures/delivery rates (gallons per minute?) depending on the station I'm at. Some fill relatively slowly while others others really crank it in. The faster the delivery rate, the earlier the system will shut off.

Just a thought.
Steve R.

 

Everything you always wanted to know about fuel tanks but were afraid to ask, from the National Institute of Standards and Technology (NIST):

http://ts.nist.gov/ts/htdocs/230/235/archive/B-014.pdf


One quote that caught my eye:

"Attempts by drivers to fill the fuel tank beyond the pump's automatic shut-off point can result in fuel being drawn into the pump's or vehicle's vapor recovery systems."

 

Yup, heard that one before. Whether or not I've ever had that problem, I can't say. Considering that when I've topped the tank, I'm not leaving the pumps rubber seal hard down on the filler neck of the car, I hold it in a position where I can see what's going on, so I'm not too worried about having contaminated the vapor recovery system of the pump. As for the car's, I've not noticed any unusual symptoms one way or the other and I tend to believe that I would have somewhere along the way so I'm not convinced that I've hurt the car's vapor recovery system either. I could be wrong. With me, it's just a habit that goes "way" back to when we didn't have to worry about vapor recovery systems!

So far on my Civic, I've added about two gallons to the tank "after" the first auto shut off of the pump. The last fill up clicked off at around 8.9 gallons. I put right at 11 gallons in the tank total and still came up with a 31.7 mpg average. If I'd done the calculations at that 8.9 point, I would have gotten 39.1 mpg!! Hmmmmm, gotta think about that one again!

Just kidding, that tank wouldn't have been valid because I topped the previous tank too. I'll have to try a "no more than the first auto shift off" fill up for a few tanks to see if I see any significant difference one way or the other.

On a previous conversation: CivicStealth, you getting close to posting your results on that "no AC, windows open" tank? I'm really curious to see what your results are!

Drive Safe,
Steve R.

 

Well, I tried to do the windows down, higway speeds test, but my efforts were foiled by the real world (DAMN! Can't we just keep this theoretical!).

At any rate, I end up at 40.84 MPG for the same course. HOORAY! Cheaper to to run with windows open than with AC!

BUT....

I could only maintain an average speed of 65 mph, sometimes 75, sometimes 55 and at two points traffic came to a complete halt.

So, not a valid test in my book, even though it came out almost one MPG over AC/Windows up.

I have to admit I've been frustrated by this...if I was not so taken up by work (war on terrorism, kids in college, wife wants to redecorate) I think I could more easily gather data.

But then, can't you imagine Newton saying the same thing? Whoops! He was a bachelor. How about those Wright Bros?

Anyway, thanks for hanging in ther with me. I'm not in favor of overfilling the tank past the vapor/overpressure barrier. Did you read the article on gas tanks from NIST? It looks like any tank of any size will click off your gas station nozzle at "full" time, so they'll all be the same--except for Ethano (curse its name) and high temperatures.

DON'T OVERFILL. Go with the click.