In an earlier thread, I was trying to understand why the miles-per-gallon calculated by the car was higher than the actual (i.e., how many miles I drove between fill-ups divided by the actual gas I put in)

I can understand the calculation being off a bit in any single tank, particularly if there wasn't a complete fill one time and the car took more gas another.

BUT...

As I compare the computer readout with my actuals over several consecutive tanks, I'm ALWAYS coming up with a difference.

Simply put...

The car is regularly reporting MPG approximately 2 higher than what I compute.

Last tank was almost pure highway. Drove 383.5 miles. Car said my MPG was 30.1 as of the time I pulled into the gas station. I expected to take something like 12.7 gallons. Instead, I took more like 13.6 - MPG turned out to be 28.2

If this was a one time fluke I'd shrug it off - but now I'm thinking there's just something unreliable in how it calculates MPG.

Have others had a similar experience with the car over-reporting its MPG?

 

The car is always going to be a little more optimistic. I track my mileage and have noticed the same thing. Essentially, it boils down to the fuel sensor in the car being more optimistic than it should be.

 

Which is also why it indicates low and the light comes on early. Better conservative than sorry.

 

everyone knows that the computer readout is always wrong(regardless of car)...the only real way is to do it the old fashion way and fill up your car(reset mile counter) drive around for awhile, then top it back off at the sae gas station and pump..

divide the miles driven by gallons used.

 

Mine is always 1 to 2 MPG optimistic as well.

 

Just out of curiosity... What year models do you guys own that have this issue on?

 

I have a 06 and mines Mine has always been at least 1 to 2 MPG optimistic.

Later

 

do you realize that complaining about 29mpg instead of 31mpg is like splitting hairs? who cares? 2 less mpg over a tank = ~30 miles less. i'd say that you guys shouldn't worry about $2 every time you fill up, but then again, i see more and more posts about how you're 18 and daddy bought your TSX, how it won't go 167mph, etc etc.

ugh.

 

Well, im not really complaining or anything, but i could see 30 miles less is about 1 gallon, and if you fuel up every 3-4 days, thats a difference of 104 gallons to every year. Then again, its only about 300 bucks difference every year, which is basically 1% of the car

BTW, I haven't seen any posts lately regarding a 167mph tsx o.O?

 

It was just a post that some kid was on here asking about if the TSX was electronically governed becuase he took it up to 120mph and it woudln't go any faster. Everybody basically responded with

 

My 2005 has always done this. The issue is that the computer is wrong and that it can be and is accurate on other automobiles. Also, on mine the displayed current MPG on the computer is so jumpy as to be unusable. Again, this works fine on other cars I have driven.

My only other complaints involve the GPS navigation, but I guess that is another thread.

The car itself is great!

 

My MID says an average MPG of 18-19MPG, and when I do it the old fashioned way I caculate 18-19MPG. Now.....don't get me wrong, I am not happy with this....should be getting at least 20-23. I do mostly highway mileage. Anyone else find these low MPG with 3G TL's?

PS: Love the car in every other possible way


Edited: Sorry just realized this was a TSX forumn

 

How do you know the gas pump is accurate? That is just one more variable to consider. Maybe you only pumped in 12.7, but they charged you for 13.6, if it errs in their favor, I doubt they'll be in any hurry to recalibrate it. I have no idea what the standards are for those things, just throwing out another thing to consider. Years ago, before cars had computers, we would always fill up at the same gas station, and use the same pump, to maintain as much consistency as possible for figuring the mileage, however, unless you fill it to the very top of the filler neck without any air space, how do you know you filled it to the exact same level as last time? One pump's auto shutoff might trip sooner than another, or one pump might pump faster, causing the fuel to foam more and that would shut it off sooner. I guess what I'm saying is, with these other variables, i'm more inclined to believe the trip computer. We have run our MDX till the Range shown was single digits ( 6 or 7 miles I think it was) We were cutting it very close, but it was accurate. I remember years ago most GM computers would show the range until 40 miles were left, and then it just said "low fuel" so when you need it most, it was useless.

 

Gas stations are regularly inspected by weights and measures agency, and they MUST comply. I can't say I've seen stations who were off too often.

 

I'm sure that's true, but how would you know if it was off ? We've all seen it where if you put a full 5 gallons in a 5 gallon can it will be flush with the threads in the cap, I can't imagine that the "full" mark would be right at overflowing, with no air space, just too many variables in my opinion.

 

-Ha. Like everyone else has said in the thread the all cars mpg readers are always very optimistic. Besides unless you go to some gas station in the hood the pumps arent likely to be off because they are required to be checked by the law twice a year(in my state).

edit - i see the moderator already replied to your post.

 

If you want to be sure, carry around a graduated can of gas, and the first 5 gals, pour it in the can to measure the pump's accuracy, then pour it back in the tank and resume your fill-up.

 

I worked at a gas station for almost two years in college. We were inspected by weights & measures four times during that period and never needed to recalibrate anything. And these were with some fairly old and crappy pumps. Unless you are filling up at a REALLY old station I doubt there will ever be any measurable drift between W&M checkups.

What I *would* expect variation in is the amount of gas you can fit into the tank on any particular day. Between thermal variations in the density of gasoline and some random factor in when exactly the pump stops I wouldn't be surprised to see a variance of half a gallon or more.

 

Maybe the takeaway is simply this...

The MPG calculation on the car will always lack precision - and if you're looking for precision, you're out of luck.

However, if you want a good guideline, it is useful.

(e.g., 29 vs 31 is splitting hairs, but 29 vs 23 makes a difference)

 

http://www.kron.com/Global/story.asp?S=4118380

Do gas pumps cheat?

 

That's another good point, and I'm not sure about the TSX, but I had an issue with a 95 Jetta running out while indicating 1/4 tank. The shop replaced the tank thinking it had deformed due to tempurature variations and physically reduced it's capacity due to being one of the first plastic tanks, I guess they just didn't have any experience with them. It ended up needing a new instrument cluster (to replace the fuel gauge) but maybe that is a valid concern with some plastic tanks ? Or maybe they just were grasping at straws ?