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Discussion Starter · #1 ·
With the T8, I'm seeing three different numbers, though I don't have that may miles on the vehicle, shouldn't atleast two of these three be identical?


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The TM on the dashboard starts from whenever the trip computer is reset (via the button at the end of the left side steering wheel stalk). The number shown on the "Driver Performance" app in Sensus starts from whenever it is last reset. But note that there is a check box in the corresponding settings to reset data after each trip. If this is checked, then anytime the vehicle is stationary for more than 4 hours, the counting starts over.

So, the first two can be very different.

I don't recall how the Volvo On Call app considers the start.

p.s. on the dashboard, you can also choose TA, which has its own logic for considering the start of data for calculating fuel efficiency.
 

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VOC will be for a given trip. Also all mpg calculations are based originally on the metric L/100km. You won't notice this until you get to very high mpg figures. 1L/100km equates to 235mpg. The next lower mpg number displayed will be 213.6mpg.
 

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I end up doing the miles per gallon (MPG) calc the old fashioned way: record mileage (or km for you metric folks) at every gas fillup. The old fashioned way says 46 MPG (over 6000 miles) while Volvo On Call says 49 MPG. I have no idea how Volvo calculates MPG . . .
 

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I switch my TM to calculate L/100 and reset every tank every tank, In winter I average about 7L/100km summer I get about 5.4 to 4.8L/100km I find that's the best way to get real world mileage.
 

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I end up doing the miles per gallon (MPG) calc the old fashioned way: record mileage (or km for you metric folks) at every gas fillup. The old fashioned way says 46 MPG (over 6000 miles) while Volvo On Call says 49 MPG. I have no idea how Volvo calculates MPG . . .
Car computers estimate based on fuel flow. There will always be a slight difference if you track MPGs between fill ups manually (miles driven/gal at pump) and use the trip computer TM average to compare. It also makes a huge difference if you just fill up to where the pump shuts off or if you risk “topping off” and potentially damaging the carbon evaporator cartridge. Our Volvos tend to be on the optimistic side most of the time about about 5%. Boxster is closer typically off from actual by 10-15% also on the optimistic side. Every once in a while they match actual miles/gal at the pump.
 

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Our Volvos tend to be on the optimistic side most of the time about about 5%. Boxster is closer typically off from actual by 10-15% also on the optimistic side. Every once in a while they match actual miles/gal at the pump.
Why is Boxster "closer" if it is off by two-to-three times as much?
 

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The VoC is the closest to real life consumption since it takes into account more miles driven. I was actually recording all trips from day one and everytime I refuelled checked the amount of liters in the tank. The mpg at the end of the year was not that different between real life and VoC.
The TM records since the last time it was reset.
The TA records since the engine starts and continues if you do not park the car for longer than 4hrs (I think). Past the 4 hrs it resets automatically and starts recording from scratch.
 

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Why is Boxster "closer" if it is off by two-to-three times as much?
Sorry, late night post - didn’t proof... I meant to write something like: closer to 10-15% off. Should have just said, “is usually more wrong than actual by 10-15%”. It also has the biggest variability from actual based on driving style.
 

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I am also having some discrepancy in mpg calculation and not sure why so much difference. I did a 550 mile road trip today and my TA showed 32.6 mpg for this trip but when I did tank refill and calculated based on full to full, it shows I only got 28.6 mpg. My last refill was only yesterday evening and put only 10 to 15 miles before the trip. Any idea why so much difference?

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I am also having some discrepancy in mpg calculation and not sure why so much difference. I did a 550 mile road trip today and my TA showed 32.6 mpg for this trip but when I did tank refill and calculated based on full to full, it shows I only got 28.6 mpg. My last refill was only yesterday evening and put only 10 to 15 miles before the trip. Any idea why so much difference?

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That’s likely because TA wasn’t cumulative for the whole 550 mile drive you completed vs TM which is if you last reset it at the prior fill up/the last time you reset it. It’s the Automatic Trip meter versus the Manual Trip one. The way the TA one works is cumulative for the recent drives and automatically resets to start over after about 4hrs of not driving/off. You’ll find more info about the difference between TM and TA in the owner’s manual.
 

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That’s likely because TA wasn’t cumulative for the whole 550 mile drive you completed vs TM which is if you last reset it at the prior fill up/the last time you reset it. It’s the Automatic Trip meter versus the Manual Trip one. The way the TA one works is cumulative for the recent drives and automatically resets to start over after about 4hrs of not driving/off. You’ll find more info about the difference between TM and TA in the owner’s manual.
It's confusing but to make my question simple, I reset my TM when filled up and took the readings at the next fill up and the readings between Volvo and my full to full calculations are way off. So not sure which one to believe?

426miles - TM says 26.9 MPG, tank refill took in 17.78gallons which translates to 24 MPG.



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It's confusing but to make my question simple, I reset my TM when filled up and took the readings at the next fill up and the readings between Volvo and my full to full calculations are way off. So not sure which one to believe?

426miles - TM says 26.9 MPG, tank refill took in 17.78gallons which translates to 24 MPG.





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Well that also raises the issue of reliability of the pump readings. In my country often fuel stations found to have trigger mechanisms to pump air inside the fuel tank together with fuel charging you for more than what you actually think you have refuelled.

Truth must be somewhere in between
 

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Thought I read today in the manual that a TM reset only resets the miles driven.... but could be mistaken


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Discussion Starter · #15 ·
Ok, so a couple hundred more miles on the car and they're lining up closer now... Anyone know what's up with VOC showing 15gallon gas tank?


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It's confusing but to make my question simple, I reset my TM when filled up and took the readings at the next fill up and the readings between Volvo and my full to full calculations are way off. So not sure which one to believe?

426miles - TM says 26.9 MPG, tank refill took in 17.78gallons which translates to 24 MPG.


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If you're resetting TM at each tank fill up, then that's your most reliable reading of miles drive, efficiency, and average MPH for each full tank of fuel you purchase. If you read your manual it may help you understand better how TA works. In a nutshell it automatically resets itself automatically after about 4hrs of inactivity which is why it's only good for current trip activity or current day activity depending on your daily routine. Look it up and you'll not be so confused ;) - also the Driver Performance is yet another way to track efficiency. I like using that one to track the "life to date" efficiency but you can also set it to auto reset after each drive. All of this is in the manual if you're interested in demystifying them and knowing more about the details and then come up with your way of using them to help you track how you drive.
 

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If you're resetting TM at each tank fill up, then that's your most reliable reading of miles drive, efficiency, and average MPH for each full tank of fuel you purchase. If you read your manual it may help you understand better how TA works. In a nutshell it automatically resets itself automatically after about 4hrs of inactivity which is why it's only good for current trip activity or current day activity depending on your daily routine. Look it up and you'll not be so confused ;) - also the Driver Performance is yet another way to track efficiency. I like using that one to track the "life to date" efficiency but you can also set it to auto reset after each drive. All of this is in the manual if you're interested in demystifying them and knowing more about the details and then come up with your way of using them to help you track how you drive.
When I said confusing, I meant your analogy of my initial post. TA and TM I understood recently after going through the manual multiple times. What I am trying to find is why there is so much difference in MPG calculations between Volvo and tank to tank.

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Oh wait, now you're really getting into the weeds without checking if you've reset both at the same time. Experiment and you'll see. The Driver Performance will tell you over how many miles it's calculating. Lower in the screen of Driver Performance screen it'll tell you how many miles have been driven. The snippet you're showing of 110.8mpg is over the distance recorded in the lower portion of that pane. Odds are the distance for the 110.8mpg indication doesn't match the distance being tracked in the Trip Computer's TM odometer.

I use,
  • the TM to record mpg, mph, hours driven, and distance between fill ups
  • TA to monitor trips during the day, typically my morning commute vs. afternoon commute since by the end of the day if I didn't run errands or have to travel between buildings at work it will have automatically reset
  • Driver Performance to track lifetime MPG, distance, hours - although lifetime since it landed in the US and not since our OSD

The key is they're all independent and at least TM and Driver Performance can be set to match or you can use them to track different things. For example, you could use Driver Performance to track a vacation (multi-day road trip as an example) and TM to track each tank. I think once you realize that they're not coupled you'll be less concerned about the fact yours don't seem to match out at any given time. RTFM if you remain confused and none of the collective experience here seems to be helping you, or experiment a little by resetting them at different times and intervals. They work well and report accurately based on fuel flow, driving style, etc. How the trip computer actually tracks efficiency is in the manual, too.
 

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I am getting no where on this inconsistent fuel consumption thing. My full tank to full tank calculation shows 17 MPG where my Volvo says 25.5 for the same miles in TM. Why is the difference so much? Isn't it misleading with so much difference?


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It also makes a huge difference if you just fill up to where the pump shuts off or if you risk “topping off” and potentially damaging the carbon evaporator cartridge.
Thanks for this tip, I also heard this from a non-Volvo mechanic so I'm assuming it's likely valid for our Volvo . . .
 
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