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Discussion Starter · #1 ·
Ok so....99.9L/100Km. What the heck?

both my wife and I struggle (in pleasure that is!) to get the best possible efficiency out of out car and we are getting very adept at maximizing the fuel we do use and this comes hand in hand with learning how the car functions best in various situations et al blah blah.

However in the first 5mins of operation (esp. now that it's getting colder) the car will run the gas motor for a couple of mins we assume to warm the "juices" and get everything up to operating temp and so on. Unfortunately the "current" usage reads 99.9L/100Km during this period (usually the first 5mins) and that actually seems to register towards our average!! That cannot be correct at all. There is no possible way ANY car could be that inefficient to use basically 1L per KM equivalent.

Can someone explain this glitch in the matrix? Exactly what is happening during this period of operation and why / how could it be possible to use 1L per Km of fuel during idle. This to me seems to be a falsehood and it's unfortunate because it ruins our average that we strive so hard to achieve with our new found "Prius driving prowess"(tm.).

Help!
 

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John,

if you use any fuel at all while the car is at a stand-still, you get an euqation that looks like x / 0 which in practical terms is 'infinity' meaning as long as you continue to remain where you are, no amount of fuel burned will get you there...

That said... keep track over the next 5 - 10 tanks ... compare the MFD averages with the actuall amount you pour into the tank... (keep totals to eliminate tank by tank errors) ... You should find that the MFD is accurate to within about 3%...
 

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Discussion Starter · #3 ·
very interesting. Infinity eh? Archimedes woud be proud!

So then it actually does get counted towards our average then??! We have been keeping records of every tank so far but still the fact that we go from 5.2 to 6.7 after we run the heat (due to the infinity value you mention) to me seems bunk even if it's not completely true which is what I think you are saying?!

Can you re-comment on that if possible?

tx!
 

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In the U.S. version where miles per gallon is reported instead of litres per mile, we get the infinity thing when the car is moving but the ICE is off. In that case, it reports 99.9 miles per hour, dto the inversion of the numerator and denominator. It seems a lot more satisfying to be getting infinite gas mileage from time to time, rather than consuming an infinite amount of fuel to go nowhere.
 

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John Burke said:
very interesting. Infinity eh? Archimedes woud be proud!

So then it actually does get counted towards our average then??! We have been keeping records of every tank so far but still the fact that we go from 5.2 to 6.7 after we run the heat (due to the infinity value you mention) to me seems bunk even if it's not completely true which is what I think you are saying?!

Can you re-comment on that if possible?

tx!
The overall average will be the amount of fuel consumed divided by the total miles driven. The fact that there is a period where you aren't moving just means that the number of gallons is going up but the miles is not. They are both running averages. Theres is no point in time where it is "calculated" so there is no way or need to throw out any data. It is also true that when the temperature goes down, the car does consume more fuel to keep the engine and the cabin up to temperature.
 

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John Burke said:
very interesting. Infinity eh? Archimedes woud be proud!

So then it actually does get counted towards our average then??! We have been keeping records of every tank so far but still the fact that we go from 5.2 to 6.7 after we run the heat (due to the infinity value you mention) to me seems bunk even if it's not completely true which is what I think you are saying?!

Can you re-comment on that if possible?

tx!

Yes, I am saying that it's not 100% true...it's merely the 'best representation' to what's happenging... but in the end, it all balances out

Also, remember at the start of a tank (or soon after a reset) the fluctuations will be much greater than after a few hundred km..
 

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Discussion Starter · #7 ·
tx. I still think it's lame that the design of the car (as much as I love it!) jumps to max possible fuel comsumption at idle which the gas motor is engaged. I know that actually the motor isn't using the equalivent of 1l/1Km but this is what goes into teh overall average. It shoudl read what is accurate where the fuel that is burning to warm teh engine(s) say is approximate to. Measured by the intake to teh engine (i'm not a mechanical engineer so this is not my problem to actually deal with I am just reporting it! :roll: ). what would be more accurate would be a readout that looks like this:

20L/0Km

.......instead of teh average ruining 99.9L/100km which is not actually true and is misleading. Nonetheless you are correct it does even out in teh end but 99.9 running for 5mins can take a 5.2 toa 6.7 in literally as i said 5mins. I just think there must be a better way to represent this accurately.

anyhoo tx for the feedback you guys.
 

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When standing still, idling at a stop light or while warming up in the driveway, all cars consume huge quantities of gasoline (more that 1 liter) to go 1 kilometer. Why? Because they're burning gas but not making progress toward that kilometer. In fact, they could burn the entire 45 liters in the tank and still not finish the first kilometer. When it comes to gasoline consumption, it's better to move than stand still.

That's why cars which cannot stop their engine while sitting still get such lousy consuption numbers compared to the Prius in city driving. Remember, city driving is at lower speed, so much less air resistance. Thus, if it weren't for the waste of idling (while stopped or moving very slowly in a traffic jam), all cars would get better city consumption numbers than highway consumption numbers.
 

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You are thinking that the car is taking the number 99.9 and incorporating it into your average mathematically. This in fact is not happening.

You are seeing 2 different formulas in operation.
1. your instantaneous and 5 minute readings:
1a. instantaneous: fuel used/KM driven within 2 seconds. If you are at a standstill, this will max of course, even if you used a teaspoon of fuel!
.000001/0 is still infinity.
1b. fuel used/miles driven over 5 minutes. See 1a, except the numbers will be a bit larger, and you may have some miles in there, instead of 0.

2. Tank average, or average since reset.
This is STILL fuel used/KM driven.
Even if 1a shows 99.9 even though you used only .00001 liters, that .00001 liters is added to your tank average.

Lets say your idle used .1 liters, and you drove 2 KM somehow.
This is not unreasonable, as even with 4L/100KM, you would consume .08L in 2 KM.
Also, your tank average is 5.6L/100KM before you idled, and you have 20KM on the 'clock'

So your 5 minute consumption is .5L/100KM but your instantaneous can still be maxed at 99.9.
You used 1.12 liters so far for your 20KM travel.
Now you used 1.23L for 22KM travel.
New average: 5.59 L/100KM.
 

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Dan, RSnyder, and melgish have all had good explanations.

Let me try to explain it a fourth way.

Let's use the Imperial units, which is what I see in the U.S. When I am in a similar situation, I see "0.0 MPG" Which means I am going ZERO miles per gallon of gasoline. That is exactly what is happening. I am going nowhere for my burning of gas. "99.9L/100Km" is just the metric equivalent. (It's what the car shows instead of 'infinity'.) No, it's not the best way to display it, but it would require significant extra programming to get it to say "?/100Km" instead. (edit: Sorry, that's supposed to be an infinity sign not a question mark, apparently this board doesn't like the infinity sign.)

The Imperial (U.S.) version has the opposite problem. While the metric version can display 'ultra-low gas use' numbers reasonably well, the Imperial version hits "99.9 MPG", even if you are using gas. (So the guys that managed to get 110MPG a few months ago had to use a plug-in tool to see what mileage they were actually getting.)

Basically, when it says "99.9L/100Km", take that to mean "using gas but not getting anywhere." The car keeps track of total gas used per total kilometers, so this 'instant' discrepancy doesn't matter over the course of the tank. (In fact, if you let it idle for 5 minutes using gas the whole time, then drive 5 minutes on pure electric, you will see one five-minute span at "99.9L/Km", and a second five-minute span at "0.0L/Km"
 

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redwein said:
In the U.S. version where miles per gallon is reported instead of litres per mile, we get the infinity thing when the car is moving but the ICE is off. In that case, it reports 99.9 miles per hour, dto the inversion of the numerator and denominator. It seems a lot more satisfying to be getting infinite gas mileage from time to time, rather than consuming an infinite amount of fuel to go nowhere.
I have the ScanGage and under some of these conditions the engine is running. I often see M.P.G. above 99.9. This data apparently comes from and/or is calculated from the CAN Buss. What you see on the MFD may not be what is going one. At the least there appear to be many times when the ICE is rotating and it does not show up on the MFD. Is it actually consuming fuel? I have no idea the scan gage suggest it is but it a device that is wedded to older technology.
 

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The scan guage is probably measuring MPG from the vacuume reading, but it may also be taking it from the injector timing.
The vacuume reading could be false, as you could be just rotating the engine at idle or greater speed, which would create a vacuume.
Taking MPG from injector timing can't go wrong, assuming the correct volume per unit time is assumed. Another source for fuel can be from the evaporative emissions system, but that should be negligible.
 

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This subject reminds me of this "math problem":

Abe drives around a 1 mile track at 60 mph.

Bob drives half way (i.e., 1/2 mile) at 30 mph. How fast does he need to drive to catch up with Abe?*

The answer to this may illustrate you can't average km/L or mpg, but have to invert it to L/km or gal/mi before averaging.

* The answer is not 90 mph![/i]
 

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At what point is Bob supposed to catch Abe?

Assuming a simultaneous start, at the 1-minute mark, Bob is 1/2 mile behind since Abe has done one full lap. 1800MPH might catch him up really fast, but 75MPH would do it eventually too...
 

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If you use another monitor such as the ScanGage you will see differences between that and the MFD. First the engine running when the MFD shows it off. Everyone should know that when they are sitting at a stop light in cold weather and the engine stops several min. after the MFD shows it off. Also on the ScanGage it can often show 127MPG, 22OMPG, etc when the MFD shows 99.9. I have absolutely no reason to believe one over the other but it is an observation. I would add that the gallons per hour on the ScanGage reflect the speed and the MPG, as you might expect, Not a conformation but interesting.
 

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mikepaul said:
At what point is Bob supposed to catch Abe?
OOps, I left out a key fact, thanks! Bob is supposed to catch Abe at 1 mile. Unfortunately, Abe crosses the line when Bob is only half-way. So the answer is infinity mph.
 

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I agree, the MFD only shows the engine running when power is actually being utilized from it, though I suspect it doesn't always show MG1 charging the battery unless you are parked.

The MFD's max MPG is 99.9. Last I knew, 127 and 220MPG is greater than the max 99.9 so 99.9 is correct for the limitations of the display. Maybe they could have shown 99.9+ when it is over, and something else when ICE is not consuming fuel at all, like --.-

MPG on the scanguage, as well as gallons per hour (assuming it is instantaneous or very short interval) is a valid indication that the engine is 'running'. RPM is not a valid indication, as the ICE can be made to spin without consuming fuel.
 

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Now that cold weather has arrived I am not sure that the ICE is not running to generate heat. With the ScanGage I am seeing more and more often the ICE running on ScanGage with the Gallons per Mile at .1 -.4 at a stop and the RPM at 900+ to 1400+. The MFD shows the ICE stopped but I can "feel" it running and if I turn off the tunes I can hear it. Conclusion the MFD is unreliable to indicate ICE function. I would like other arguments on this thesis.
 

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Again, MFD will only show if ICE is running for electric or kinetic power. Waste heat that is otherwise utilized for our or its comfort is not included.

What you would then need to monitor is MG1 electrical output and MG2 RPM. If both of these are 0, but ICE fuel consumption is >0, then it is running for heat.
 
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