Hyundai Sonata 2015 Driving Cost Analysis

just married

I‘ve been keeping track of my gasoline and maintenance costs since I purchased my 2015 Hyundai Sonata. As of writing this article, the car is about 875 days old and I’ve visited the gas station 78 times. With a 2.4L 4-cylinder engine getting 185 hp, the advertised combined MPG is at 28, with 24 city and 36 highway.

Every time I filled up, I recorded:

Threw it all into a Google Sheet and calculated some metrics to see if I could gain anything interesting from the data. I wanted to see how much it costs to use this vehicle over time as well as how my driving habits affected those costs. I always drive in Eco mode, except on rare occasions when I’m going up a steep path then I’ll go into Sport.

Here are my results!

Note: Starting July 1, 2016 I moved and began taking the bus to work. That shaved my commute from 32 miles to 2 miles a day (still drove to the bus station). As you’ll see, this event is very apparent in the charts and will be the basis of most of my analysis. I also drove to Las Vegas the same weekend so you’ll see a spike in distance driven at that moment.

Days and Distance Driven Between Fill-ups and MPG

A nice overall view of my driving habits. As noted, prior to 7/1/16 I was primarily commuting 32 miles a day for work, mostly by highway. When I started commuting by bus, you can see that I didn’t have to get gas as often. My MPG dipped as a result of driving shorter distances and mostly locally. Average distance driven between fill-ups moves with my MPG.

You can break up MPG into Cost per Gallon and Cost per Mile.
MPG = CPG/CPM

Cost per Gallon

The gas prices I paid (blue), as well as the local retail price from the EIA (red). I live in Los Angeles. Steadily creeping up…and it seems I mostly overpay. Chevron with Techron ftw.

LA Retail Price Source: U.S. Energy Information Administration https://www.eia.gov/dnav/pet/hist/LeafHandler.ashx?n=PET&s=EMM_EPMR_PTE_Y05LA_DPG&f=W

Cost per Mile

How much it costs to drive my car per mile. It heavily depends on the cost per gallon but note that it starts to creep up a lot faster than the price starting in January 2016. Not sure what the exact cause is but it’s very likely a combination of wear and tear of vehicle parts plus less conservative driving as I’m getting more comfortable with the car.

Odometer

Odometer over time. The trend clearly changes after 7/1/16. If I project using only the data up to 7/1/16, my mileage today (September 2017) should be around 33,000. The mileage I save by taking the bus adds up to a lot over time!

Miles per Day

An estimated average number of miles I drive per day, which is based off calculations per fill-up. Realistically it’s less than 5 miles every weekday and large spikes over the weekends. The weekend of 7/1/16 was the trip to Las Vegas.

Cost per Day

Cost per Mile multiplied by Miles per Day. It looks like it’s decreasing overall which is good. The decreased amount of driving is overcoming the increased cost of driving. This includes maintenance costs like oil changes, filters, and tire rotations too.

Driving Efficiency

I tried to come up with a metric that could measure how efficiently I was driving. The Efficiency Index compares the [current cost per mile relative to the total average cost per mile] to the [current cost per gallon relative to the total average cost per gallon]. The difference between these two indices tells me how much better or worse the cost of my driving was while taking into account the cost of gas at that time. The more positive the number is, the more efficiently I was driving.

The early months of driving saw very low efficiency due to the high cost of gas. Once that was alleviated, my driving efficiency shot up. Over time however, the cost per mile steadily increased (mentioned above, likely due to wear and tear and less conservative driving).

I have no control over the cost of gas, so how effective does a change in driving habits affect my total cost? The next chart will show!

Discussion: I needed a way to quantify the aggressive/conservative nature of my driving. Obviously MPG is the catchall result, but was there something underlying that could help me see how the driving habits affected MPG itself? The component of MPG that shows this is cost per mile, but unfortunately that depends on the cost per gallon. By finding the difference between their respective relativities, I can separate out the effect of driving…but it also factors in the effect of price. Not a perfect measure for what I wanted to do with the MPG analysis, but in the end it does provide some nice info on my overall efficiency!

MPG Compared to Driving Efficiency

This is the last chart, I promise. Due to limitations in Google Sheets, I couldn’t label things properly while trying to split the data in the same column into two sets. The blue dots represent MPG prior to my move on 7/1/16 and the red dots represent the MPG after the move. The horizontal axis is the driving efficiency index from the previous chart.

Very clearly, switching from normal combined driving to mostly local leads to a 4-5 MPG impact. The effect of driving conservatively vs aggressively might make a difference of up to 3 MPG if you drive strictly locally. But it doesn’t seem to make much of a difference when driving combined – cruising on the highway washes it out. Data is still a bit too scattered to be sure though.

Blue – Combined Driving, Red – Mostly City Driving

Summary Stats (as of September 2017)

• Odometer = 25,514 mi
• Total gallons filled = 909.23
• Total cost = $3,058.03
• Combined MPG = 28.06
• Avg Cost/Mile = $0.12
• Avg Miles/Day = 29 mi
• Avg Cost/Day = $3.49

Conclusion

• I’m performing as expected compared to the advertised MPG. I’m about 1 MPG above advertised.
• Having moved from normal driving to significantly decreased driving made a good comparison between combined vs city. Pleasantly surprised at how much insight I gleaned from just 4 pieces of data.
• Cost of gas is slowly creeping up.
• I’ve driven ~7,500 miles less than expected in the last year between taking the bus vs if I were to drive to work.
• I might be driving more aggressively over time, and I suspect wear and tear is affecting my mileage too.
• Due to decreased distance driven and fewer highway miles, my average MPG has gone down.
• The above two points led to my cost per mile to increase significantly.
• Despite that, my cost per day is decreasing due to overall lower average miles driven per day.
• Driving habits have little effect on my MPG, if driving combined. Moderate effect if driving mostly locally. Stop-and-go traffic has a greater effect on my MPG than whether or not I drive aggressively/conservatively. (Driving conditions vs driving habits)

Well, thanks for hanging in there and reading. Hope you found something as boring as MPG a little bit less boring.