I use fuel buddy app. I put the fill up info called for and it works out the same as if I calculate it myself.

Another long trip! Fuel Mileage update.

Actual mileage considerably less than what the gauge indicated.

Fuel economy gauge showed 23.3, actual MPG was 21.7. Driving only on freeway cruise control set at 81 with a crosswind.

Higher gas consumption should be expected if cruising @ 81 (mph) with a crosswind....that's just north of 130 Km/hr, a speeding offence here in Canada... Our max legal speed limit here is 100 Km..100kph= 62.13712 mph that's quite a difference...not condemning your speed, just saying at 81 mph you can expect the 2 mile loss due to speed, wind resistance and other factors!

5.0 Candy, I don't think Roboref was complaining about the mileage he was getting rather he was stating that the mpg he calculated manually did not agree with what the trip computer was telling him. I have kept track of my own gas mileage manually ever since I got my first car in 1979 (when trip computers were not available) and for the majority of cars I have owned, my calculated mileage has always been less than what the trip computer calculates.

I understood it the same way....and did not see his post as a complaint either...I was merely bringing to the table that these other variables tend to slip by what the onboard computer calculates, I calculates mine manually as well and pretty much find the same thing,not sure if it's a system glitch or it's designed to report slightly more inflated numbers to pacify customers.
As a perfect example, hit the reset button back to zero when you're driving in 6th gear @ say 100 km/hr...it will start adding up pretty quickly,BUT take your foot of the gas, and it will start to lower those numbers pretty fast....does that mean you're actually running on less fuel? not exactly....it's looking at air mass sensor, fuel pump pressure,fuel air mixture, cam position and timing and assuming a given number, or at least that's how I understand it!

The mpg I calculate manually is always less than what the onboard trip computer calculates....just as the mpg reported by the manufacturer is always higher than what is actually achieved.

First the speed limit was 75 mph and you can routinely run at 81-83 and not be stopped ( have passed numerous policemen without issue). Love wide open spaces in Texas and New Mexico!

I am glad to get the additional information on the algorithm for computing the MPG. I am somewhat surprised that it is still not more accurate though with the upgraded electronic monitor available. This was the same trip that we made in September and the calculated MPG was still higher with mostly same conditions. I was hoping with the additional miles driven that the MPG might go up some.

This vehicle is a replacement for road trips of a 2005 MB e320 and with its 6-cylinder engine driving the same way, same trip we could get 25 MPG albeit with premium fuel. The other thing that is puzzling is the calculated fuel mileage is about the same for city driving ( within 1 mpg), which doesn't make sense. I am going to try driving a segment on our next trip to Texas at a 75 MPH cruise just to see. I know every vehicle has a sweet spot for speed to optimize mileage.

Just sharing experiences.

Just did a trip from NH to Montreal over Thanksgiving weekend and averaged 23.2 with snow tires on it, 18".

Mainly speed limit drive, 55-70, due to weather conditions.

Was averaging 22.1 on the daily drive but that was on the summer tires.

I have a 2015 MKC 2.0 FWD. My lifetime calculated MPG over 20,584 miles is 24.45 MPG. My highest MPG on a tank of gas was 31.71 in August 2016. My Lowest was 20.85 in December 2015. I've had 4 tanks of 30-32MPG and all were on trips - meaning 100% highway driving.

At some point in there, after reading the Premium might give me better MPG in one of the posts one this board, I tried premium gas for several months. The MPG breakout was Regular 24.42 MPG (Based on 17.3M miles) and Premium 24.91 MPG (Based on 3.2M miles). Not a huge difference in MPG so I use regular considering the cost difference of around .40 cents a gallon.

The MPG calculation that the MKC makes (and every car I have ever had with this feature) is typically 1-2 MPG higher than the actual calculation. On the 31.71 MPG tank, it was quite a bit higher at 36.2 MPG.

FWIW, since I have had the smartphone app, my lifetime MPGs have been:
2005 Jeep Wrangler Unlimited - 15.74 MPG (regular) - High 18.67 MPG on a trip
2005 Chrysler 300C Hemi - 17.81 MPG (required mid-grade 91 octane) - High MPG 25.64 on a trip (used cylinder mgmt to shut down 2 cylinders on highway driving)
2007 Jeep Wrangler Sahara 4-door (manual transmission) - 17.3 MPG (regular) - High MPG 20.72 on a trip
2010 Acura MDX - 20.59 MPG (required premium 93 octane) - High MPG 25.12 on a trip
2011 Jeep Wrangler Sahara 2-door - 16.8 MPG (regular) - High MPG 19.61 on a trip
2013 Lincoln MKZ Hybrid - 41.08 MPG (regular) - High MPG 44.78 daily driving (trips killed the MPG on the Hybrid, daily driving yielded best MPG)
2015 Lincoln MKC 2.0 FWD - 24.45 MPG (mostly regular) - High MPG 31.71 on a trip
2017 Lincoln MKZ 3.0T FWD - 22.63 MPG (regular) - High MPG 28.86 on a trip

KenZ thanks for some serious science there.
My 2015 2.0 MKC FWD, now at 43,000 miles, has settled into an average just over 27 mpg. ( I have a 2 lane fairly rural commute at 50-60mph mixed with Interstate on half my weekends at 78:-) )
I stay on Regular unless towing my 2500lb boat, then I go Premium and suffer at 16mpg. But the power is quite adaquate.
Without a doubt, there was some fairly significant loosening up of the drivetrain over the last 10k miles: the average used to run in the mid 26s.
Top up your tire pressure at least once a month.