Calculating ICE vs Electric Miles

Northerner · Feb 14, 2023

Washingtonian said: ↑

I calculate mine a little differently. I bought mine new March 30, 2017. Since then I have a small book kept in the door panel where I write down the amount of gas and date for every fill up. I have added gas 28 times in the last 6 years for a total of 220 gallons. At an average cost of $3.50 per gallon that is $770. for gasoline. I roughly average 50 mpg, so 220 gallons of gas equals 11,000 miles. My total mileage is 25,500, so I assume the remaining 14,500 miles is on the traction battery. Between Summer and Winter I can go an average of 24 miles on a full charge. At 13 cents per KWH it costs roughly 80 cents to charge the car at home, which where It has always charged. 14,500 miles divided by 24 miles means I have charged it 604 times. 604 times eighty cents equals $483. for electricity. Looking at those numbers, it costs me $770. to go 11,000 miles on gas or a cost of 7 cents per mile. It cost me $483. to go 14,500 miles as an EV, or 3.7 cents per mile.
Of course there are a lot of fixed costs which have nothing to do with mileage, such as depreciation, insurance and license fees plus tires, a new 12V battery and oil and filter changes.
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I’d be interested to know something from you:
Does your car report the lifetime MPG? If so, you can calculate how much gas your car thinks you’ve used (since it was new) by dividing total miles by the MPG (eg, this is 88.8 mpg for my car). It would be interesting to see how that number compares to the number of gallons that you actually purchased according to your records.

Salamander_King · Feb 15, 2023

Northerner said: ↑

So my 2020 Prime reports that, overall, I have 37000 miles at 88.8 mpg.
If I were to assume 55.5 mpg for the ICE alone that means the rest of the miles were electric- so 3/8 electric and 5/8 gas powered.
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I can see your math, but your assumption of 55.5mp could be wrong. On a PP, it is just not possible to "look up" the gas-only mpg.

Northerner said: ↑

Does your car report the lifetime MPG? If so, you can calculate how much gas your car thinks you’ve used (since it was new) by dividing total miles by the MPG (eg, this is 88.8 mpg for my car). It would be interesting to see how that number compares to the number of gallons that you actually purchased according to your records.
Click to expand...

Here is the record of my past three Prius Prime lifetime data along with three other HEVs I have owned.

For example, the lifetime overall MPG of 2021 PP displayed was 104.2mpg for a total of 12678 miles driven. That means the car thinks 121.7 gals of gas were used. The actual gal of gas used was 127.8 gal. What car displays are on average ~5% more optimistic. This is true for all three PPs and two other Hybrid Gen3 and Nissan Pathfinder Hybrid. HCH did not have the lifetime mpg record on the dash.

Northerner · Feb 15, 2023

Salamander_King said: ↑

I can see your math, but your assumption of 55.5mp could be wrong. On a PP, it is just not possible to "look up" the gas-only mpg.

Here is the record of my past three Prius Prime lifetime data along with three other HEVs I have owned.
View attachment 237253

For example, the lifetime overall MPG of 2021 PP displayed was 104.2mpg for a total of 12678 miles driven. That means the car thinks 121.7 gals of gas were used. The actual gal of gas used was 127.8 gal. What car displays are on average ~5% more optimistic. This is true for all three PPs and two other Hybrid Gen3 and Nissan Pathfinder Hybrid. HCH did not have the lifetime mpg record on the dash.
Click to expand...

This is a very interesting post. I like it that there is only a five per cent error on the value the car calculates versus what the real gas consumption was! I am not surprised, however, that the error is on the “optimistic” side. Of course it is.
I acknowledge that an even bigger error might be introduced by my assumed lifetime ICE mpg… which I, confusingly, assigned two values for in my opening post. I first used 55.5 because it made the math easy for me when I noticed that the car registered 88.8 mpg: 5/8 ICE and, therefore, 3/8 electric. Later in that opening post, I used a different more realistic value … after thinking about winter here in the north. I reduced the ICE mpg to 50 mpg. It’s admittedly based more on a feeling than any sort of integrated analysis of real data, but that gave me 44% of my miles as having been driven using electricity rather than gas (rather than 3/8).

Salamander_King · Feb 15, 2023

Northerner said: ↑

This is a very interesting post. I like it that there is only a five per cent error on the value the car calculates versus what the real gas consumption was! I am not surprised, however, that the error is on the “optimistic” side. Of course it is.
Click to expand...

I kept a detailed record of all data displayed on the car and also gas pumped. Here is the breakdown of each fueling for my 2021 PP. Total of 16 fueling in ~15 months. As you can see, the car displayed mpg (read from Trip meter reset each refuel) can be off in either direction. So trusting the mpg displayed on a single trip can make a bad estimation.

left column number is calculated by distance traveled/gal gas pumped and the second column is read from the car Tripmeter corresponding mpg for the same distance traveled between fueling.

Northerner said: ↑

I acknowledge that an even bigger error might be introduced by my assumed lifetime ICE mpg… which I, confusingly, assigned two values for in my opening post.
Click to expand...

Since there is no easy way to look up the HV-only mpg on the PP, what I ended up doing was calculating the HV-only distance based on the electricity used for charging and car displayed efficiency data. Below is the final number from my 2021 PP. Everything is calculated except the lifetime miles/kWh which is displayed on the Drive Monitor 2. In my case, it was 5.0 miles/kWh from there everything else is known as numbers. The only thing is that I have made an assumption based on data corrected previously that from the wall it takes to charge the battery from 0% to 100% only 84% of that kWh actually ends up in the traction battery due to conversion loss, and other BTM functions.

Based on that assumption and the data I collected, the 2022 PP over ~13kmiles got 58.24mpg. The actual EV/HV ratio was 41% EV/ 59% HV.

assykay · Feb 17, 2023

Washingtonian said: ↑

I calculate mine a little differently. I bought mine new March 30, 2017. Since then I have a small book kept in the door panel where I write down the amount of gas and date for every fill up. I have added gas 28 times in the last 6 years for a total of 220 gallons. At an average cost of $3.50 per gallon that is $770. for gasoline. I roughly average 50 mpg, so 220 gallons of gas equals 11,000 miles. My total mileage is 25,500, so I assume the remaining 14,500 miles is on the traction battery. Between Summer and Winter I can go an average of 24 miles on a full charge. At 13 cents per KWH it costs roughly 80 cents to charge the car at home, which where It has always charged. 14,500 miles divided by 24 miles means I have charged it 604 times. 604 times eighty cents equals $483. for electricity. Looking at those numbers, it costs me $770. to go 11,000 miles on gas or a cost of 7 cents per mile. It cost me $483. to go 14,500 miles as an EV, or 3.7 cents per mile.
Of course there are a lot of fixed costs which have nothing to do with mileage, such as depreciation, insurance and license fees plus tires, a new 12V battery and oil and filter changes.
Click to expand...

Yeah Buddy, I also got the same calculation. Thanks for sharing your thought just before me so I get my accurate results confirmed.

Calculating ICE vs Electric Miles

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Calculating ICE vs Electric Miles

Northerner Active Member

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