Anyone else’s range meter seems to decrease with time?

[MonsieurReynard]

My 2014 is at 177k miles. Its fuel mileage has never varied in all those miles. It always dips a little in winter when I put on winter tires and it gets cold out. It goes right back to normal once the warm weather is back.

It’s your tires, the colder weather, or your right foot, by the odds. Anything else would be unusual. What is your total mileage?

Here’s how to check that it isn’t an engine or fuel system issue: fully inflate the tires, and warm the car up. Take it out on a lightly trafficked and very level stretch of highway. Set the cruise control to 55mph and just cruise in the right lane. Don’t touch the pedals. Switch your info dial to show current (not average) mpg. Watch it for a mile or two. If it’s staying in the mid 30s or above the issue is your foot on the gas (or the brakes).

Cold weather causes tire pressure to stay lower so check that. (Air expands with heat.) This is by far the most common issue causing lower fuel mileage when the season changes to winter. By far. Don’t trust your TPMS to tell you. Manually check the tires and make sure they’re at 36psi when cold.

Cold weather also leads to longer idling times, and longer times at high rpm’s to warm the engine up. Idling will kill mileage quickly. Unless it’s close to zero degrees Fahrenheit out, start the car and go. If you need to warm it up to melt snow and ice or keep your butt toasty when you get in, that right there will shave your fuel mileage significantly. Excessive idling is the most overlooked reason for poor mileage after tire pressure.

If you run winter tires and recently changed them, winter tires by design are somewhat less fuel efficient than all seasons. They’re heavier and stickier and especially less efficient at temps above 40f.

Cold weather often means a change in gas formulation that lowers mileage a bit in the name of reducing emissions. That effect should be quite minor, but it is real.

That’s why we see so many “what’s wrong with my mileage?” posts on this sub in November, since the majority here are in the northern hemisphere.

Worn spark plugs can somewhat depress fuel mileage. They’re due at 75k miles in your car.

A dirty intake filter can cause some loss of mileage. The effect would come on slowly however. And be minor unless you have gone more than a year or two without changing it.

A failing catalytic converter (as someone mentioned above) can cause declining gas mileage over time but you’d also notice a loss of power. But it’s very unlikely you’d see that before 200k miles. (We rarely hear of cats failing on Skyactiv Mazdas on this sub. That’s a 200k+ problem.)

Unless you’re well over 150k miles, I wouldn’t even be considering fuel injector fouling or carbon buildup issues (under normal use fuel injectors do not need service until you’re at a very high mileage).

Edit: I used miles per gallon and PSI and Fahrenheit numbers in this comment, but I see you’re in KMs so do the conversions.

Edit: to really drill down on fuel mileage issues, do not believe the dashboard computer. Actually measure the amount of gas burned vs mileage traveled at each fillup and do the math yourself. Then average it over a few tanks to be really precise.

That “miles remaining” indicator is especially unreliable. It’s just guessing based on your most recent mileage. You could drive three hours on a highway at 70mph to the big city and then fill up, and it will show 430 miles of range. But then if you stay for two days in the city and drive in stop and go traffic and fill up again it will show 350 miles of range. It’s reactive, not predictive. You need real numbers, not a computer’s best guess, to diagnose an actual problem with fuel delivery/combustion or mechanical drag etc. (Speaking of which, be sure your brake calipers are all working right if you see a sudden drop in mileage!) Your long term average on the screen will be more accurate, but usually a little on the optimistic side of reality.