Honda Insight Forum banner

1 - 20 of 21 Posts

·
Registered
Joined
·
31 Posts
Discussion Starter #1
Is anyone seeing totally off-the-mark instrument calculations? I have an '01 5-speed, and on a recent 800+ mile trip across the country the MPG gauge for the trip was registering on the order of 57.5. Actual manual calculations done with an ordinary calculator at fill-ups were more on the order of 48.

Yes, the manual calculations were done beginning with a full tank, and calculating at subsequent fill-ups.

Now, I'm not necessarily crying at 48 mpg. It's a far cry from the 22 - 25 I see with my other vehicles. But 57+ would certainly be more desirable.

No lights are lit on the dash. Tires seem properly inflated.

Where might I start to get my manual calculations more in line with the computers'? I am new to Insighting. Perhaps there's a thread in here somewhere which the rest of you are more familiar that might read off a list of 10 or 15 things the beginner can check on his own.
 

·
Premium Member
Joined
·
9,861 Posts
I don't think you are using the trip buttons right.
Explain more.
 

·
Registered
Joined
·
938 Posts
just a hunch. you may be looking at the lifetime mpg. Like Willie said. more info would help (what mpg screen/mode ect are you veiwing)
 

·
Registered
Joined
·
31 Posts
Discussion Starter #4
Well, I was using the range MPG function- the function that shows a double-sided arrow, as such: <=====> I simply reset the mpg which, as I understand it, calculates an mpg over a specific distance, from point A to point B. I reset it to 0 when I filled up, and after having driven 600+ miles over a 800+ mile course, the dash was registering 57.5, but manual calculation was more on the order of 48. By the time I was 600+ miles away from my starting point, I had stopped twice to fill up. Each fill-up was for about a half tank. I simply added up the two fill-up gallon purchases, and miles driven up to that point / gallons purchased = close to 48 mpg- a considerable discrepancy over the dash calculation.
 

·
Registered
Joined
·
2,009 Posts
If you are continuing to fill your tank after the filler nozzle clicks off, you can start to fill the charcoal evaporative control canister with liquid gasoline. Gasoline from this canister, normally only vapors from the tank unless the tank is overfilled, is sucked into the air intake and, therefore, doesn't pass through the injectors. This fuel vapor-rich air causes the amount of fuel injected by the injectors to be reduced to maintain the proper air-fuel ratio. The amount of fuel that passes through the injectors is used to calculate fuel efficiency. Therefore, the reported fuel efficiency can be higher than it actually is if you overfill your tank. Might this explain your fuel efficiency discrepancy?
 

·
Premium Member
Joined
·
9,861 Posts
To get a better (closer) reading, you should have reset the mileage at each fill up. Then divide the amount to fill up into the mileage shown.

HTH
Willie
 

·
Hypermiler
Joined
·
3,650 Posts
Well, I was using the range MPG function- the function that shows a double-sided arrow, as such: <=====> I simply reset the mpg which, as I understand it, calculates an mpg over a specific distance, from point A to point B. I reset it to 0 when I filled up, and after having driven 600+ miles over a 800+ mile course, the dash was registering 57.5, but manual calculation was more on the order of 48. By the time I was 600+ miles away from my starting point, I had stopped twice to fill up. Each fill-up was for about a half tank. I simply added up the two fill-up gallon purchases, and miles driven up to that point / gallons purchased = close to 48 mpg- a considerable discrepancy over the dash calculation.
The double arrow you refer to <====> along with an mpg indication is likely the lifetime mpg (lmpg) and the number of miles the car has been driven with that lpmg. (readable by activating the fcd button?, left side of dash) As soon as my lmpg updates itself with a new figure the mileage resets itself to zero. (about 400 miles ago my lmpg improved to and reset itself to 50.0 mpg, and the mileage next to the arrow symbol reset itself to zero.)

Use your trip button, right side of your instrument panel (left of the kph button), to get accurate indications of mileage and mpg per trip / tank, dependent on how you use it. I find my 'tank fill' (actual) mileage to be very near identical to my trip meter (indicated) mileage.

Do you still have an owners manual ? Good descriptions are in the om for trip meters.

..Bob
 

·
Registered
Joined
·
4,008 Posts
The double arrow <====> indicates segment mode... the FCD button mode.

Sent from my Nexus S using AutoGuide.Com Free App
 

·
Premium Member
Joined
·
2,825 Posts
I think the dash MPG calculation is a fairly good approximation ... if you want to do better by all means ... but that is much harder than most people think.

Most gasoline Pumps when tested by your state department of weights and measures only has to be within 2% to pass with no fine ... ie get that little date sticker on it... when it reads 10.000 gallons you might have 9.8 gallons or 10.2 gallons and still pass and get a sticker in some states.

Depending on your state some pumps that fail only get a fine and are not taken out of service ... while other states take the pump out of service ... but even if a given pump were say 10% off and taken out of service ... the gas station doesn't give anyone a refund ... etc ... the best that happens is that they get fined and the pump gets taken out of service until its error % is small enough for your state standards.

Also what provides the energy is the molecules ... sense a given number of molecules has a set mass but not a set volume ... volume of the same number of molecules varies with temperature and pressure.

So , if you want to get a very accurate MPG count the 1st thing ... is a highly accurate method of measuring the amount of fuel put in ... the best method is a precision scale ... weigh the empty container ... weigh the combined ... ___ milligrams of fuel were added.

As other have said there is also a potential issue with gallons until the tank is full ... officially the I1 Gas tank is 10.6 Gallons ... but there are people who have pumped over 13 gallons in.... so is pumping 10 gallons full ... or 13 gallons full ... well it turns out they are both full... another good reason not to use a more abstract concept like 'full' and instead a more precise measurement like ___ Milligrams.

Also the distance counter is based on an assumed circumference of a tire ... but a newer tire will cover more inches per rotation than a worn tire for the same number of rotations... so the best way to know the distance is with a more accurate method ... like a measured mile... GPS can be good , but don't make the mistake to think it is 100% ... every form of measurement has a +/- margin or error / resolution limit.

But that's just my two bits.
 

·
Registered
Joined
·
1,814 Posts
My gas calculations are usually very close to what the display shows. Typically the display is less than 2% off from what I calculate. My calculations are typically a little lower than the fcd, but sometimes the fcd is slightly lower. I have also read that temperature affects the actual amount of gas, that the pumps are calculated at a given temp (72?). I believe I read an article that people in Canada have complained that ov a year time frame the average temp is less than the cal temp, so in the long run they are getting jipped. People in warm states might be getting more than they are paying for.
 

·
Registered
Joined
·
155 Posts
Very often I find that different pumps will fill up my tank to different levels. If I calculate my mpg manually and come up with a low mpg average, on average the very next time I calculate at fill up it will come up high. If I divide the two it comes up to what my fcd shows. Trust the fcd!

Sent from my DROID RAZR using AutoGuide.Com Free App
 

·
Registered
Joined
·
1,732 Posts
My gas calculations are usually very close to what the display shows. Typically the display is less than 2% off from what I calculate. My calculations are typically a little lower than the fcd, but sometimes the fcd is slightly lower. I have also read that temperature affects the actual amount of gas, that the pumps are calculated at a given temp (72?). I believe I read an article that people in Canada have complained that ov a year time frame the average temp is less than the cal temp, so in the long run they are getting jipped. People in warm states might be getting more than they are paying for.
If I remember correctly about the USA pumps, the oil companies said it would cost too much to put the temperature compensated pumps in.

Except in Hawaii, where I think the state demanded they put them in and it wasn't too much to do. :p
 

·
Moderator
Joined
·
6,933 Posts
On average, the FCD is accurate to within 1%. But it can swing as much as like 8%.

For me, at least.
 

·
Registered
Joined
·
17 Posts
Just did my first full tank in the car: display showed 57.1, fillup calculation added up to 57.0958. :)
 

·
Registered
Joined
·
4,008 Posts
I've tracked the FCD in my HCH1 over 21000 miles now (every fill up, actual mpg and the displayed FCD recorded).

The result: The FCD is actual MPG + 1.99.

I also tracked my I1 the same way over 36000 miles.

The FCD was actual mileage + 1.08.

Sam
 

·
Registered
Joined
·
131 Posts
If I remember correctly about the USA pumps, the oil companies said it would cost too much to put the temperature compensated pumps in.

Except in Hawaii, where I think the state demanded they put them in and it wasn't too much to do. :p

This seems so ironic since Hawaii has the smallest temperature variation of any place in the states. In the 14 months I lived there I don't remember it ever being over 90, usually not over 85. And it seemed like a cold snap when it got down below 70 at night and I had to shut the windows to stay warm. Where buildings typically don't have AC or heat, demanding temperature compensated pumps seems foolish.
 

·
Registered
Joined
·
1,732 Posts
Cold vs warm gas

Gasoline expands when it warm and there are less molecules per volume than if the fuel was cooler. Therefore cold states/Canada get more energy per gallon of fuel by volume (the pumps dispense fuel by volume) than warm states if the pump isn't temperature compensated.

At the same time the station storage tanks are typically underground and the temperature is more stable underground (which is normally the average temperature of the location). Admittedly the storage tanks are usually under the pavement at the station and that might increase the temperature at the tank in sunny, warm states.
---

Honda emissions canisters are usually pretty small and I can't imagine that the Insight canister and it's hoses can hold ~3 gallons of fuel. Typically the canister is higher than the top of the fuel tank so liquid fuel shouldn't get into it.

[After studying the blow up drawings of the Insight fuel system.]
There is also a "two way valve" which allows air to enter the tank as fuel is used up but builds up a little pressure in the tank before it releases air (or perhaps fuel) into the canister. The ECM tests for that pressure and will throw a MIL if the air pressure doesn't exist (for instance if you don't tighten the gas cap properly).

But there might be enough fuel separator volume in the gas tank to hold a gallon or so if you put the fuel in slow enough. It would depend upon how far the air vent tube from the filler pipe extends down into the fuel tank (which creates the separator area), if the car is level etc.

In a good fuel system design the two way valve would be attached to the very top of the fuel separator volume so under a normal filling session no liquid fuel should be able to get to the canister. If nothing else the air pressure in the fuel separator won't be high enough to pass through the two way valve.

I usually fill my cars by slowing the fuel flow down when the tank is within a gallon or so of where the nozzle is going to kick off. Then I even the $$.xx up to some amount and stop. I also try to go to the same station/pump if possible.
 

·
Registered
Joined
·
1,732 Posts
This seems so ironic since Hawaii has the smallest temperature variation of any place in the states. In the 14 months I lived there I don't remember it ever being over 90, usually not over 85. And it seemed like a cold snap when it got down below 70 at night and I had to shut the windows to stay warm. Where buildings typically don't have AC or heat, demanding temperature compensated pumps seems foolish.
[conspiracy theory] I wouldn't doubt that the gas companies didn't mind doing it because they could then claim that the new pumps didn't save people money. [/conspiracy theory] ;)

Especially so when you see this,

The table below displays the average monthly temperature in Honolulu Hawaii.

Temperature by: Fahrenheit
Honolulu Temperature Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Annual
Avg. Temperature 72.9 73.0 74.4 75.8 77.5 79.4 80.5 81.4 81.0 79.6 77.2 74.1 77.2

The average year round temperature is only 5° above the pump certification temperature.
 

·
Premium Member
Joined
·
9,861 Posts
1 - 20 of 21 Posts
Top