Consumption & AVG MPH Display

Each trip odometer (A and B ) has it's own stats that are updated while the car is in READY mode (i.e. "on"). So CONS MPG is the MPG you've gotten and AVG MPH is your average speed.

Some people assume that the MPG and MPH are only calculated while you're moving, which would actually be misleading.

 

MPG is Miles Per Gallon and MPH is Miles Per Hour. Not much to explain.

 

The MPG is your average gas consumption that you have attained in all of your driving. And the avg MPH, is just the average speed when factoring all the different speeds that you travel

 

An earlier poster alluded to the fact that the MPG and MPH numbers are being calculated so long as the car is in Ready position. What this means is that even when you are driving 70 on the highway, you'll not see anything nearly so high as your average MPH, because you start and end at 0 MPH, and it takes some time to get up to speed and down to a stop. The same thing applies to the MPG calculations.

 

I still share the same confusion as the person who posted the initial question, regarding one basic point related to the "CONS" MPG number on the 2010 Prius instrument cluster. Is the number calculated for the entire time since you last reset the trip odometer (which would make the most sense), or does it calculate for the past 15 minute or 30 minutes, or some other algorithm?

It makes the most sense that the number would be since you reset the trip odometer, but the owner's manual does not say, and only refers to the 1 minute (showing 15 minutes of history) and 5 minute (showing 30 minutes of history) "past history" version of the display, which has the same "CONS" number at the bottom as the Hybrid System Indicator display.

 

The "CONS MPG" under the A or B trip odometer is averaged from the time you reset it. For instance, I reset the B trip odometer every time I fill the tank to get an estimate of my MPGs for the tank. I use A to see a lifetime average. Many people use variations of this. Therefore, it does not average it every 1-5-10 minutes, it is averaged from the time you reset your trip odometer for A or B.

 

what about 5 mins calculations? every first 5 mins stays around 20~ mpg, 50~ mpg afterward. is that about right?

 

I'm not sure you are being clear. The important thing is that consumption mpg and MPH are calculated from whenever you reset trip A or B. So if you set trip A 500 miles ago, you get the averages since then. You are correct that time sitting in ready mode, and not moving, is averaged into the figures.

 

Here's the variation I use. I reset the B trip odometer at each fillup. I use a spreadsheet to track my lifetime mileage and also the difference between the Prius MPG calculation and the pump calculation. I use the A trip odometer for single trips or as a daily average so I can see how my mileage correlates to certain routes and speeds or my daily commute.

 

I'm still at a bit of a loss to understand how the average MPH display is working. Something is awry.

I get that it's basically taking the number of miles you've driven, the number of hours that the vehicle has been in READY position and dividing one over the other.

Here's what I don't get.

So about 50 miles into a new tank I took my lunch break in the Prius. I kept the car in READY position for 1/2 hour and the average MPH did not change from 28. The number of hours changed by .5 and the number of miles didn't, so it should have gone down.

This morning I noticed on my drive to work, the average MPH read 37 when I got on the freeway and by the time I was at work it read 35. Yet I was on the freeway the entire time and didn't slow below 40MPH for more than a minute or so. The mph should have gone up.

There's something wrong here, either with my expectations or with the display.

 

This is surprising to me, as well. Since your car was in READY mode and not ACC or IG/ON, I would expect the data to continuously update. Did you check to see whether the 1- or 5-minute consumption bars were being updated?

I have a hard time believing this could be the case, but I suppose it is possible the time factor is, literally, rounded to the nearest hour before the calculation is made. If that were the case, then your half hour would not make a difference (you were at 1.8 hours before and 2.3 hours after -- both would round to 2 hours).

The other option is that you were looking at a consumption screen from a trip odometer that wasn't reset at your fill-up, but it continued on. At your average speed, once you get up to about 600 miles on the trip odometer, a 30-minute stop is not necessarily going to make enough of a difference to change the average speed. For example: 600 miles for 21.1 hours averages out at 28.4 mph, rounded to 28. 600 miles for 21.6 hours comes to 27.8 mph, or 28.

Unless you have a very short ride on the freeway, were at the start of a tank, and had several blocks of slow, side-street traffic getting to work, I can't come up with numbers to help explain this one.

I suggest there also could simply be a lack of knowledge on our part about exactly how and when the calculations are made.

 

Thanks for the well-thought-out reply.

I hadn't checked the 5-minute numbers, I'll look at them today. At the moment I'm about halfway through a tank so changes aren't as obvious as they would be at the beginning of a tank. I do know that the trip meter had been reset at the last fillup and the MPG numbers were acting normally (which is to say, extremely responsive to changes in driving.)

Sadly, my ride on the freeway is over forty miles each way and I m quite certain that it read 37MPH as I entered the freeway and 35MPH when exiting.

Your theories are excellent and I really do appreciate them but this is just hinky.

 

I agree. It sounds a bit odd.

There's always a chance you've made an error or saw things the wrong way. Perhaps you could keep a log for a few days, writing down the basics from the consumption screen: Miles, MPG and MPH.

I do this for each tank and for each change in driving (city to highway), but I also do it for every little trip I take when it is reimburseable. I have lots of numbers around, and they all seem to work out fine.

And we can't escape what is right infront of us: It could be that something just isn't right in your system, because your numbers don't work out very well.

 

If it's just me, and just that one display, I don't care much. If other people are seeing this problem, it would be interesting to find out.

 

I've noticed that when the car is in drive, but I'm stopped at a stop light, the MPH reading can decrease. You may need to have the car in drive in order for it to register???

 

Well, I sat in the car for 30 minutes with it in Park and READY. The average MPH did move from 35 to 34 about 20 minutes in, and the 1min consumption gauge did keep moving. It still doesn't "seem right" but again, I'm not super worried about it. However, if I were doing it, I wouldn't count the time the Prius was standing still. I'd say that average speed is only the average when speed >0.

 

I would almost agree with that -- well, really, no. No, I think I'll disagree. Well, maybe . . .

The problem here is that although the ICE may not be running and no gasoline is being consumed, gasoline will have to be consumed to recapture the energy used while in Ready mode. It works this way in standard cars, and they are not usually measuring ave mph in accessory mode. But they DO measure it when the ICE is running.

I could see having the feature inactive unless the car is in gear, but there are plenty of times where the ICE will be running even with the car in P.