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Put me down as seeing about a 5% difference between real world and what the car says. We have calculated mileage so many times I now just subtract about 1 MPG from the computer and figure that's about the true number. FWIW we get about 20 to 21 MPG on our 2.0t on average.
 

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2019 Santa Fe Ultimate 2.0T HTRAC
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5% is a reasonable tolerance due to the many inaccurate (5% lol) data in manual calculation.
 

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Don't mean to bust anyones bubble - - but the MPG readout on the dash is 99% accurate.
Seems not everyone agrees with you:
 

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More examples:
 

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2020 2.4 SEL FWD
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@2019SFRED

Interesting discussion here about the Holy Hyundai computer. I ain't buying it but maybe mine needs a flash. Yet another thing for the list to cover during my initial dealer service visit. Some people may swear by the absolute accuracy of computers but I've been using them on daily basis for more than 30 years. I know better.

According to the Hyundai programming, my car made 31.9 MPG over the previous 749 miles. This picture of my display takes the car back to the last reset of this screen after filling at 318 miles. The math says the car made 30.56 MPG. I actually used 24.51 gallons. If the car was really making 31.9 MPG, I would have used 23.48 gallons.

For a slightly deeper dive, we can go back to 165 miles and the very first fill of the car on 12/21/19 when I started keeping the records. 902 miles. To travel these 902 miles I used 29.729 gallons. If the car was actually getting 31.9 MPG, I would have used 28.27 gallons. So, either I put 1.46 gallons in my boots or the certified and inspected Top Tier pumps (Shell) I use have collectively robbed me for 1.46 gallons over these five fuel fills. I don't think so. They were certified in December. I looked today.

So here's yet another 5% discrepancy. This time between the fuel actually used and the fuel I should have used if the car was really making 31.9 MPG.

Another thing about this trip computer seems very strange. With a freshly filled tank, the Hyundai programming gives me a DTE range estimate of 453 miles. With an 18.75 gallon tank and the car telling me it's getting 31.9 MPG, seems like the car would project a range of something more like 575-600 miles. Not 453 as shown in the picture taken at the gas pump.

My ancient Dodge Intrepid R/T does a much more accurate job at this task with its 16.9 gallon tank and typical average of 28.3 MPG. It gives me a DTE of 450 miles on a fresh fill.

The carputer does tell me something else interesting. When the engine is running, I keep the car moving along at an average of right at 40 MPH with my mostly country road driving to the various cities and towns I visit. I reckon I should be getting a lot better than the EPA estimates but I don't believe I'm getting as good as Mama Hyundai wants me to believe. Time will tell.

444974


If anyone thinks the gauge says the tank isn't fully filled per the picture above... that's parallax. Here's one taken after I got home with no parallax.

444975
 

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@2019SFRED

Interesting discussion here about the Holy Hyundai computer. I ain't buying it but maybe mine needs a flash. Yet another thing for the list to cover during my initial dealer service visit. Some people may swear by the absolute accuracy of computers but I've been using them on daily basis for more than 30 years. I know better.

According to the Hyundai programming, my car made 31.9 MPG over the previous 749 miles. This picture of my display takes the car back to the last reset of this screen after filling at 318 miles. The math says the car made 30.56 MPG. I actually used 24.51 gallons. If the car was really making 31.9 MPG, I would have used 23.48 gallons.

For a slightly deeper dive, we can go back to 165 miles and the very first fill of the car on 12/21/19 when I started keeping the records. 902 miles. To travel these 902 miles I used 29.729 gallons. If the car was actually getting 31.9 MPG, I would have used 28.27 gallons. So, either I put 1.46 gallons in my boots or the certified and inspected Top Tier pumps (Shell) I use have collectively robbed me for 1.46 gallons over these five fuel fills. I don't think so. They were certified in December. I looked today.

So here's yet another 5% discrepancy. This time between the fuel actually used and the fuel I should have used if the car was really making 31.9 MPG.

Another thing about this trip computer seems very strange. With a freshly filled tank, the Hyundai programming gives me a DTE range estimate of 453 miles. With an 18.75 gallon tank and the car telling me it's getting 31.9 MPG, seems like the car would project a range of something more like 575-600 miles. Not 453 as shown in the picture taken at the gas pump.

My ancient Dodge Intrepid R/T does a much more accurate job at this task with its 16.9 gallon tank and typical average of 28.3 MPG. It gives me a DTE of 450 miles on a fresh fill.

The carputer does tell me something else interesting. When the engine is running, I keep the car moving along at an average of right at 40 MPH with my mostly country road driving to the various cities and towns I visit. I reckon I should be getting a lot better than the EPA estimates but I don't believe I'm getting as good as Mama Hyundai wants me to believe. Time will tell.

View attachment 444974

If anyone thinks the gauge says the tank isn't fully filled per the picture above... that's parallax. Here's one taken after I got home with no parallax.

View attachment 444975
Your methodology of checking MPG over multiple fill-ups goes a long way towards validating your conclusion, especially when it comes to variations with when the gas pump kicks off. However, DTE indicator might not be based on long term computed MPG so I’m not sure it contributes to the overall MPG error discussion. In my other car, the DTE is based on the MPG over a fixed number of previous miles - something like only the last 60 miles. The SF might be doing something similar and also looking at other factors. Per the SF Owner’s Manual:

“The range may vary significantly based on driving conditions, driving habits, and condition of the vehicle.“

This implies to me that they’ve got more to their algorithm than just multiply long term mpg by number of gallons in the tank.
 

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Better to have the DTE be pessimistic than the other way around.
Anyway, I wouldn't really care about its reading until it goes under 100 miles. Maybe more if I were in Montana.
 

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2019 Santa Fe Ultimate 2.0T HTRAC
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Carputer result has average algorithm applied. Manual calculation does not. The two results cannot be same. However, the error should be consistent.
 

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So here is the rub.
Every car's gas tank design is different. We had a 08 Versa that would take 10 litres after the first pump click to actually fill. A friend has a cruze that can take 6 and yes just yesterday Our 19 SF's can take 5.25 litres after the first click on a gas pump, it might have even taken a bit more I stopped when I saw liquid. More of an experiment really.

As the fuel sloshes around in the vehicles tank this causes variations in gas level during filling. causing the gas pump to click off at various points. Not really knowing when you tank is actually full.

To Gates - - this might be where your missing gallon is, you never pumped it back in. The gas pump "thinks" your tank is full.

I have said this before the only way you could actually tell that you are filling your tank to full and that you are replacing what was used is to weight the car during filling.

Many of these articles do not address this - - - I honestly can not see why. It is a basic dynamic principal.

Our gas pumps have not changed much at all in decades. Liquid flow return and pressure will turn them off.
 

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‘19 Santa Fe Ultimate 2.0T FWD (Machine Gray/Espresso Gray)
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So here is the rub.
Every car's gas tank design is different. We had a 08 Versa that would take 10 litres after the first pump click to actually fill. A friend has a cruze that can take 6 and yes just yesterday Our 19 SF's can take 5.25 litres after the first click on a gas pump, it might have even taken a bit more I stopped when I saw liquid. More of an experiment really.

As the fuel sloshes around in the vehicles tank this causes variations in gas level during filling. causing the gas pump to click off at various points. Not really knowing when you tank is actually full.

To Gates - - this might be where your missing gallon is, you never pumped it back in. The gas pump "thinks" your tank is full.

I have said this before the only way you could actually tell that you are filling your tank to full and that you are replacing what was used is to weight the car during filling.

Many of these articles do not address this - - - I honestly can not see why. It is a basic dynamic principal.

Our gas pumps have not changed much at all in decades. Liquid flow return and pressure will turn them off.
I’ll stick with this logic regarding over-pumping. It makes no sense to risk destroying your carbon canister filter.


 

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2020 2.4 SEL FWD
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To Gates - - this might be where your missing gallon is, you never pumped it back in. The gas pump "thinks" your tank is full.
I'm not missing a gallon. Over the 902 miles, I pumped in 1.46 gallons more than the trip computer claims the car could possibly use. As I said, time will tell.

Properly filling a fuel tank isn't rocket science. It may take a little more time but the years of filling up my diesel pickup trucks has taught me the patience required.
 

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2020 Santa Fe SEL 2.4l FWD
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I’ll stick with this logic regarding over-pumping. It makes no sense to risk destroying your carbon canister filter.
Your a smart man. On another auto forum I participate in there is currently an individual searching for help in replacing his carbon canister. He lent his van to his Father-In-Law who upon returning it wanted to be kind and pump as much gas as he could into the van to repay his Son-In -Law for letting hem borrow it. Unfortunately he pumped gas into the canister and the Son-In-Law got a check engine light indicating the problem with the carbon canister.

It is not a good thing to try and pump as much gas as you can into a car tank
 

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Learned my lesson regarding overfilling the hard way.

Had a brand new BMW with only about 1000 miles on it when the CEL came on. Dealer said the evaporative emission system was flooded with raw fuel from overfilling, and the damage would not be covered under warranty. I complained to BMW USA, and received the same response. The warning about overfilling was in bold capital letters in the owners manual.

Had to pay $1200 out of my pocket for the repairs. Lesson learned.
 

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My 2 cents worth.....
I've tracked MPG since new on my SF. The vehicle consistently thinks it gets .8 to 2.5 MPG better than hand calculation. I've tracked every fill up since new, so either the fuel is leaking or the vehicle calculations for MPG is off (I've never seen fuel leaking so calculation is a bit off). However, this seems consistent with most vehicles, including my 2016 F150. All modern vehicles are all controlled by computer and mileage is calculated via computer as well. Since my F150 was off by .8 to 1.8 MPG, did some searching on the forums and found a post where one is shown how to go into "engineering test mode" on the F150. From there, one can adjust the AFE Bias (this is what calculates the MPG in the Ford F150). By adjusting this, my truck is now -.1 to .3 MPG off from hand calculation (I've tracked MPG for over 25,000 miles). While it will never be spot on every fill-up (for many of the reasons already posted), it can and should be much closer than it is. The Hyundai (and every modern car) does have a way to get into the equivalent of the F150 "engineering test mode" where this can be adjusted. Usually, the manufacturer engineering department will not disclose this information to Dealership Service Departments unless they are working on a very specific issue, so it is not widely known that it exists, and you probably won't find a dealership that will share the information (even if they know it). However, I'm convinced there is a way to adjust the calculation since it is all computer controlled.

Just as a side, based on the information I found on the F150 Engineering Test Mode and how to adjust the MPG calculation, this was posted by someone who worked for a company with a large fleet of trucks. The company tracked miles and gas consumed, and started accusing employees of skimming fuel from the tanks. Eventually, the company turned to Ford for an explanation. Long story short, instead of employees stealing fuel, Ford Engineering stepped up and told them how to adjust the MPG calculation. Of course, then it was eventually posted on the internet..... I cannot confirm every detail I've mentioned, but I can confirm the change to the AFE Bias under the Engineering Test Mode in my truck did make it track MPG pretty much spot on. In order to get into Engineering Test Mode on the F150, there is a sequence of button and door open/close combinations that reveal Engineering Test Mode in the Speedometer Cluster. If only one could figure out how to get into Engineering Test Mode on the Hyundai, we could adjust the MPG calculation to be much close to real MPG.
 

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My 2 cents worth.....
I've tracked MPG since new on my SF. The vehicle consistently thinks it gets .8 to 2.5 MPG better than hand calculation. I've tracked every fill up since new, so either the fuel is leaking or the vehicle calculations for MPG is off (I've never seen fuel leaking so calculation is a bit off). However, this seems consistent with most vehicles, including my 2016 F150. All modern vehicles are all controlled by computer and mileage is calculated via computer as well. Since my F150 was off by .8 to 1.8 MPG, did some searching on the forums and found a post where one is shown how to go into "engineering test mode" on the F150. From there, one can adjust the AFE Bias (this is what calculates the MPG in the Ford F150). By adjusting this, my truck is now -.1 to .3 MPG off from hand calculation (I've tracked MPG for over 25,000 miles). While it will never be spot on every fill-up (for many of the reasons already posted), it can and should be much closer than it is. The Hyundai (and every modern car) does have a way to get into the equivalent of the F150 "engineering test mode" where this can be adjusted. Usually, the manufacturer engineering department will not disclose this information to Dealership Service Departments unless they are working on a very specific issue, so it is not widely known that it exists, and you probably won't find a dealership that will share the information (even if they know it). However, I'm convinced there is a way to adjust the calculation since it is all computer controlled..
Have you (or anyone else here) ever checked the odo/speedo for accuracy? Inaccuracy here would goof up the mpg figures too.

I'll have to do that the next time I make a run of more than a few miles on the interstate.
 

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Your a smart man. On another auto forum I participate in there is currently an individual searching for help in replacing his carbon canister. He lent his van to his Father-In-Law who upon returning it wanted to be kind and pump as much gas as he could into the van to repay his Son-In -Law for letting hem borrow it. Unfortunately he pumped gas into the canister and the Son-In-Law got a check engine light indicating the problem with the carbon canister.

It is not a good thing to try and pump as much gas as you can into a car tank
I agree with you, Digger and PMCErnie. Both my Santa Fe sales guy and one for my 2012 Camry 8 years ago were emphatic about NEVER filling past the first click.

I am back from a month in Hawaii followed by a big family event this past week so haven't really paid much attention to car forums since mid January but find things like this and ISG "entertaining" to say the least. I really can't say being off .5 or .8 MPG really matters to me from one method to another. After some checking almost 18 months ago when my 2019 SF was new I found the actual miles/gals was slightly higher than the computer MPG so I quit manual calculations. I looked on a long trip this weekend and over 4900 miles w/o a reset I've been averaging 25.5 on a 2.4L, probably since early last summer. I compare that to a 16 long term MPG average in a Jeep Gr Cherokee I had prior and am HAPPY with this torqueless Santa Fe that does what I need. MPGs this past weekend trip seemed a bit down, around 27-28 highway, however half the tank was top tier gas from mid January.

I plan to occasionally scan the computer MPGs occasionally, good enough for me. And the ISG still never kicked in despite 57 F in southern Wisconsin.
 

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If the manual states fuel tank capacity is x amount of gallons then you should be able to fill it to it's maximum,, it does not say to only fill to less than the amount stated.
 

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This thread has pretty much run it’s course, as well as rambled all over the place. The OP never confessed his remote start habits, but I suspect that was one of his problems.
 

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If the manual states fuel tank capacity is x amount of gallons then you should be able to fill it to it's maximum,, it does not say to only fill to less than the amount stated.
Yes but because you have no idea how much fuel you have in your tank already it is advisable to fill to first click on the pump.
 
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