The display software does report the effect of non-propulsive or energy generation only activities of the ICE in the consumption screen. Both the 30 minute history graph and the tank/trip average will drop pretty seriously if you sit and burn fuel without actually going anyplace.

The energy display shows energy paths; where the energy is coming from and where it is going. The consumption display shows exactly that, it displays instant consumption, in the form of a bar graph and then also shows 5 minute averages in bar graph form for the last 30 minutes. Additional information is stored there such as average FE, which is your true target, not instantaneous mileage, and any values associated with power regeneration from braking or coasting.

The ICE will run without moving the vehicle for 2 reasons. To create engine heat to bring the block up to optimum operating temperature, to warm up the catalytic converters (and to provide heat for the cabin) and to charge the battery should the computers ask for charging when the vehicle is not moving. One of these conditions is always displayed, ICE charging battery without vehicle movement. The other, warming up, is not displayed on the energy display. But both charging and warming up do show up in the average FE on the consumption display.

Lots of us have noticed the "discrepancy" between the display's average and the ones we calculate. I have come to the conclusion this is based upon variances on the quantity of fuel we are able to put into the tank from fill-up to fill-up. I have come to believe that the display is more accurate because it is measuring FE based upon fixed and constant measurements. We calculate FE based upon distance traveled and amount of fuel used to fill-up which can vary wildly. The car does it based upon fuel metering and actual consumption, which reduces variability significantly.

Unless I'm not understanding your desires I think the information you want is on the display, just not necessarily where you expect it.

Good luck!

 

Thanks for the reply JeromeP. I get what your saying and concur that some portion of the ICE running without propulsion is being aloowed for. I want to say your 100% right but something about this just isn't making sense to me. Maybe I'm making it harder than it is. It wouldn't be the first time. Thinking out loud - I'm remembering the display showing 0.0 mpg with the engine running with no propulsion on occasion. That is absoulutely correct but is it possible the data this is true for is being thrown out of the averaging because of divide by zero errors or that it is believed to be insignificant? I suppose that would depend on the time frame used by the SW. Am I being obtuse? I would think that changing the SW to show/calculate with 0.1 MPG and including the previously discarded data (0.1 MPG for "x" time for 0.01 miles as an example) would be more accurate in the long run and would give me my low rather than high display result for current MPG by the tank, and maybe be within 1 percent of my fill-up method of calculating it. Like I said, I'm probably making this too hard and you're probably right. I may be expecting 100% accuracy where it is not possible for the factors you mention.

 

I noticed this morning that during the 1st 5 minutes of driving (warm up time) that when approaching a stop sign the MFD indicated green battery charging flow only and 99.9 MPG, AND the engine was running. This seems to me to be the reason the tank MPG figure works out to be higher than actual MPG. If the engine is running shouldn't the display show less than 99.9 (infinite) MPG? Maybe Toyota will update the MFD and the calculation SW to show/use engine activity without propulsion or charging to allow for this one day.

 

Especially now that it has been much colder, I've noticed the somewhat anomalous condition of the instantaneous mileage showing some number less than 99.9 with no energy flow. This happens at the low end of an extended glide (20mph or less), or when I am coming up to a stop (green arrows + less than 99.9, even more strange). This happens only in the warmup period in warmer temperatures, but seems to happen consistently when it is below freezing - it seems like the ICE is less prone to shutting off completely, but you can still "glide". The first time this happened I thought it was totally unintuitive ("no energy flow/green arrows, how can the instantaneous not be maxed out??").

 

Let's see if I can respond to posts 12, 13, and 14 competently.

Locutus, I've seen the condition you describe also. It basically seems totally normal to me. The vehicle is coasting or coming to a stop, but the ICE is running as part of the warm-up sequence. So, you can't get an instantaneous full 99.9 mpg because the vehicle is consuming fuel, although not directing it to the wheels. It is then calculating the instant economy based upon your speed while coasting or braking. I think this is proof positive that the vehicle is taking into account fuel consumption while warming up.

abowles, the 99.9 mpg limit on the display is because of the divide by 0 error that occurs when trying to calculate MPG and a limitation by the system to 3 digits. miles/gallons can produce no reasonable result when fuel consumption is 0. Other software versions for countries that use the metric system often times use liters per 100 miles. Since the denominator of the equation is always populated by a value greater than 0, they actually always get a value, the lower the value the better. However when monitoring mpg, the higher the value the better. If you are truly coasting with the ICE off your instant mileage becomes infinite because you are not using fuel at all. On the other hand with the ICE running and you are coasting and you see the 99.9 value in the instant economy display, that would indicate that the vehicle is getting mileage that is better than 99.9 mpg. Some have suggested that the discrepancy between their manual FE calculations at fill up and the calculation the car uses are due to the lack of "accuracy" past 99.9 mpg, however the onboard computers store all of this information as raw values and then calculates the average FE based upon total miles driven over total gallons used.

I'm still inclined to believe that the car has a better idea of actual gallons used and as such the FE number it provides on screen is more accurate than what we generate based upon our fill-ups.

 

Thanks LocustofBorg and JeromeP for your thoughtful replies. I'm going to cogitate a little more on it for my part. One thing I started doing 2 fill-ups ago to take another variable out is to fill-up at the same station, same pump, same level of nozzle insertion (as close as possible), same clicks (1), and as close to the same temp as possible. Maybe this will match the display MPG to the fill-up MPG more closely.

 

Okay. I filled up last night and manually calculated 53.24 MPG. The MFD showed 54.5 MPG. That is ~ a 1% difference, which is a reasonable margin of error (unless your working on a trillion dollar budget ). I'm thinking my fill-up technique is making the difference there. Not an original idea. I borrowed that from someone - I'm remembering over at PriusOnline.

 

I would call that a good fill up. I bet you didn't put in more overall volume in that fill up than you did in the one just previous, i.e. the tank was filled to nearly the same level as your previous fill. Essentially that is the goal when trying to calculate mileage. If you have even an extra 1/2 gallon of fuel in the tank than when you started that could cause a pretty significant difference in MPG than if you got the levels nearly the same.

However, I doubt that anyone would be worried about this discrepancy if the vehicle informed us of how many gallons it used over the course of a tank and then we could do our own MPG calculation using miles between fillings and the fuel volume consumption over that same period. We would come up with the same number the car does. And on top of that when filling the tank we could also take into account how overfilled or under filled the tank was as compared to the previous tank.

 

Hi All:

___I do not know if this will help in the discussion or not but the Prius II does record fuel consumed and distance traveled above 99.9 mpg’s. When you are into the 100 - 130 mpg range over lets say 30 miles, you can drive off at a given FE of lets say 45 mpg and when the averaging display kicks down to 99.8 mpg, you can back calculate what you actually received above 99.9 over the 30 miles traveled previously using the reset trip mileage. This is from when you started to when you finished the > 99.9 mpg’s segment and the distance until you saw the tick down to 99.8 mpg’s while at 45 mpg’s. It worked about as good as could be expected until Ken1784’s SuperMid consumption meter arrived which did in fact take metric calc’s as far as you could possibly take the Prius II’s extreme FE at the time.

___Good Luck

___Wayne R. Gerdes