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Will anyone believe this? Do I believe this?

I am the original owner of a 1996 Plymouth Breeze with 170K- 2.0 L 4, 5 speed manual. Between Saturday and today I drove 408.2 miles- all highway, all at moderate (45-62 mph) speeds, and used 8.082 gallons of gas- 50.5 mpg. Very moderate weather- no AC, not that it works anyway. Window sticker MPG was 36 highway/ 25 city. I do drive like I’m not in a hurry, because I’m not. I believe I followed the same protocol in filling my tank both times.
I usually get in the low to mid 30’s in an urban driving situation and have seen low to mid 40’s in a similar all highway situation.

I think something is off - whether the odometer or a gas pump you used. Aside from that 400 miles isn’t really enough to go on, in part because even small changes in the amount of gas make a difference. So small changes in the sensitivity of pump auto-shut offs are in play. If you get low-mid 30s “urban” I’d buy as high as 40 on a trip like this. But not 50.

But by all means do it a few more times until you rack up a few thousand miles. If you’re still at 50 we’ll have something to talk about.

I don’t think the odometer is off- I was on a route I have taken a lot in the past, and nobody has moved Shawano, WI or Milwaukee. If the gas pump I filled up at is off- and they are selling 10 gallons for the price of 8- I’ll go there all the time. I agree that the amount I put in could vary with the auto-shut off and how much I put in after it shuts off, but by how much?

It can be off by a lot. A gas mileage reading based on 400 miles and one or two fillups is not reliable.

Thanks. I’m not sure I’ll be able to replicate the all highway, moderate speed situation real soon. Whether or not I hit 50 mpg it sure taught me the value of moderate highway speeds. There are a lot of people out there in a big hurry and I’ll bet none of them like $4.00/ gallon gas.

I suspect that the pump cut off early, and that you – being a knowledgable driver – did not try to top it off. So there was probably room for a few more gallons in there.

Yeah, just a short fill. See if the next tank is unusually low mpgs.

The best you can do to check fuel mileage with one tank is to refill at the same pump with your car parked in the same direction. Gas station parking pads can be out of level to a differing degree, making it possible for an air pocket in your tank to make an inconsistent refill in addition to the other possibilities listed. Otherwise, check fuel mileage over more than two tanks and you should do reasonably well with your calculation.

I certainly did not try to pump in the last ounce - or dollar- so there could be some room in there. The gauge- that I don’t trust a whole lot- does show it as over the F mark.

Your report is based on a single tankful of gas. Your calculations are meaningless. As others suggested, it was not a complete fill. My Plymouth’s fuel gauge used to behave the same way. You could easily have added another 2.5 gallons if you tried… and your mpg would have been calculated at a normal 36 mpg. But if you prefer to believe in a 50.5 mpg trip, I’m happy for you.

I think I started the post with a healthy degree of skepticism- I didn’t want to imply that I got 50 mpg, only that- for one reading- it looked like I did. I may have underestimated the variability in amount of gas in a “full” tank depending on gas tank position, etc. Perhaps the fact that during the first fill the trunk was full of stuff and during the second it was not accounts for a gallon or two.

A big tailwind could easily account for it too…

Well if I ever have 12 hours and $40 to burn I’ll fill it until I can reach the gas with my finger, drive in circles at 45 mph to negate the wind, and refill it to the same point. Or not.

Not being in a hurry can certainly result in vehicles breaking the EPA fuel mileage ratings, sometimes by a lot. There certainly may have been an error of some sort in your situation, or some unknown variable, but driving slow and steady will get some pretty impressive figures. My dad had an old Cavalier five speed and always drove like he wasn’t in a hurry, and could easily and consistently break 40 mpg, even with a trunk full of tools and passengers in the car. The car was originally rated for 22 city, 33 highway according to fueleconomy.gov

I think 50.5 is possible under the right driving conditions especially with the 5 speed. I’ve had several highway tanks between 45-50 mpg in my '97 Escort wagon 2.0L 5 speed manual. My best tank ever was 49.85 mpg on a cool summer day. It was cool enough I didn’t need the a/c and was driving interstate with the c/c set at 55 mph. I’ve broke 50 mpg on strictly highway trips a few times in my '88 Escort 1.9L 4 speed manual. It’s best tank ever is 54.42 mpg. I check my mileage with each fill up and always fill the tank to the cap so I know my numbers are correct. The '88 almost always get somewhere between 40-43 mpg in mixed city/rural road driving. I keep a close eye on fuel mileage so if it drops I know I have a problem and can hunt it down before it costs me a fortune in $4. a gallon gas. A few months ago I drove my mom’s '99 Mecury Grand Marquis 4.6L automatic on a road trip, the total mileage was about 541 miles and I made the complete trip on less than a tank of gas… I filled up when I left town and when I returned I filled up at the same station and had averaged about 31.5 mpg in a full sized sedan hauling 4 people and luggage.

Math error, transcription error, bad gas pump, or memory failure.

You could easily do that if it were 400 miles down hill. Otherwise, it may be a combination of slight errors on a good day when 40 mpg was reachable. My 02 Prism standard could do low forty mpg under ideal conditions you discribes. I doubt it was that much better but it does show the error doesn’t have to be that great. Do it again and write us back and we’ll all apologize. Then, resell it back to Chrysler to show them they can actually make a high mileage compact they can reverse engineer.

If the needle on the gas gauge was reading empty and it filled up with 8 gallons, I’d suspect you got lucky at the pump. Bet its fixed by now though.

You ( & we ) must ALWAYS use the law of averages over the course of several tanks of fuel.
Even using the ‘‘first click’’ theory of filling up leaves a lot of variablilty as to just how much is in there.
So you average it out through those variables.
How much fuel in tank.
Temp and weather.
Fuel quality.
tire pressure.
weight.
rates of acceleration and overall speeds.

I agree with just about everybody.( Maybe not the math error and memory failure.) Yes, if Chrysler could make a vehicle capable of 50mpg highway in 1996 they might not have had 4 owners while this car has had one. I think gas pump shutoff variability and weather and even orientation of the car at fill up play a role. If I report my next gas mileage it will be mostly city driving and not real comparable. And to get two tanks in a row of highway driving I’ll need to go 1000 miles, and who wants to do that in a 96 Breeze?