2013~2016 Weird fluctuation from CX-5 Trip Computer

[Hammer46]

Is anyone experiencing weird fluctuation in the Current MPG readings on their Trip Computer?
Mines just over 81K miles and at 45 mph on a flat highway I get huge fluctuations between 18 mpg and 87 mpg. Some times it'll read around 60.5 mpg which is about correct for that speed but then it'll bounce low into 45.9 mpg then back up to 60.5 again.

Any assistance is appreciated in advance.

 

[theblooms]

That's normal. Set it to average instead of current and it won't move like that

 

[GFrosty]

Is anyone experiencing weird fluctuation in the Current MPG readings on their Trip Computer?

Definitely normal.

The CX-5 has two calculations going: the Current value, and the Average value.

Current -- as pointed out, it will fluctuate. If you're going up a long hill, for example, the engine has to work harder and the fuel economy will be worse. Whereas if you're just plodding along at 60mph on the highway, on the flats, the engine doesn't have to work anywhere near as hard, and so fuel economy will be much better. On my own 2916.5 CX-5, I've see it as low as 3.5-4mpg briefly, if really hitting the throttle and heading up a hill. It's disappointing, I suppose, but it's normal, as that is how much fuel the engine is consuming at that time.

Average -- fuel economy over time. On my CX-5, if I reset trip "A" then it'll reset the fuel economy statistics. Whereas if I leave it and instead use trip "B" for seeing how much mileage I've done on the current tank or trip, then it'll average the fuel economy since the last resetting.

So far as I know, all the CX-5's work this way, with Current and Average.

If I'm going for a long trip, I'll reset trip "A" in order to see what the trip's fuel economy is. Else, it would get averaged-in with all the city/mixed driving I have been doing the past few months.

 

[Berniehel]

Is anyone experiencing weird fluctuation in the Current MPG readings on their Trip Computer?
Mines just over 81K miles and at 45 mph on a flat highway I get huge fluctuations between 18 mpg and 87 mpg. Some times it'll read around 60.5 mpg which is about correct for that speed but then it'll bounce low into 45.9 mpg then back up to 60.5 again.
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Any assistance is appreciated in advance.

Yeah, mine does the same! I think it’s pretty normal since the trip computer reacts to even small throttle changes, road conditions, and wind.

 

[ADS-B]

I took a long trip with my little CX-5 these days. Drove from Houston area all the way to Denver. On a 1.000 mile trip, fuel economy average was at 27.2 mpg but yesterday I was blown away: filled up the tank in Colorado Springs. From Springs to Denver, my car registered 35.8 mpg! I was blown away! This is the best mpg ever recorded on my car and I did not do anything in particular, just drove as usual, given the freeway traffic on I-25 between these two cities.

 

[GFrosty]

I took a long trip with my little CX-5 these days. Drove from Houston area all the way to Denver. On a 1.000 mile trip, fuel economy average was at 27.2 mpg but yesterday I was blown away: filled up the tank in Colorado Springs. From Springs to Denver, my car registered 35.8 mpg! I was blown away! This is the best mpg ever recorded on my car and I did not do anything in particular, just drove as usual, given the freeway traffic on I-25 between these two cities.

Is it relatively flatter, that route from CS to Denver? 800ft elevation difference, but I've no idea of the particular route's hills.

Add a bit of tailwind, and I could see the fuel economy jumping by quite a bit. Particularly if just setting things to cruise control and letting the "zoomers" pass you by.

What's appalling to me: the CX-5 fuel economy heading up the mountains through the Reno area, versus when coming back the other way. Something like ~50-70mpg typical on the downhill leg, for a couple dozen miles, versus nearly single-digits going back uphill. One of the reasons I set the "info" display to "miles to empty tank", myself.

 

[N7turbo]

I took a long trip with my little CX-5 these days. Drove from Houston area all the way to Denver. On a 1.000 mile trip, fuel economy average was at 27.2 mpg but yesterday I was blown away: filled up the tank in Colorado Springs. From Springs to Denver, my car registered 35.8 mpg! I was blown away! This is the best mpg ever recorded on my car and I did not do anything in particular, just drove as usual, given the freeway traffic on I-25 between these two cities.

Happens to me every time I drive to Colorado. First time I noticed that was in my 2000 Grand Prix with the 3800 V6. It's the elevation. Your engine takes in less oxygen-dense air. The computer mantains the AFR and puts in less fuel. Thus, less power and fuel used.

 

[ADS-B]

The computer mantains the AFR and puts in less fuel. Thus, less power and fuel used.

Thanks for the info. I knew it was due to the elevation and air density but I figured that the computer will put more gasoline, not maintaining the ratio. Good to know!

 

[ADS-B]

Is it relatively flatter, that route from CS to Denver? 800ft elevation difference, but I've no idea of the particular route's hills.

Not really, it's ups and downs, from 7000 feet to 6000, back to 7000, drop to 5500 and so on. Speaking of altitude, I was baffled by the way Mazda infotainment shows your elevation on the screen, I am talking about the 8 inches screen. You go to the "Where am I" or something like that. When I left Houston everything looked fine, elevation shown in feet. But once you start climbing, let's say you reach Amarillo, at 3500 feet, Mazda, for some weird reason, does not show your elevation in feet anymore, it shows it in... miles! At some point I checked the altitude and I was at ... 0.7 miles! Who in the world wants to have the information in miles!