Honda Fit 2016.
My dashboard usually showing an average MPG of 30. Last year 2023 I had a starter issue so I had that replaced. Then 2 weeks later, my battery which was said by another shop to be good, suddenly went out. Got a new battery. This year, I notice that my MPG was reading 23 MPG. I haven't done the experiment and calculate the MPG but I know for sure my refueling frequently has not change. I am still concern so I took my vehicle to a local mechanic I often visit. Per their recommendation I change my spark plug and paid for a fuel injector cleaning. My MPG went from 23 to 24, then 25. This month it went down to 24.5. No change in frequently of refueling. I called my local mechanic and he had no more idea of what could b wrong so I took it to the dealership. They came back with 1 issue - serpentine belt is cracked and advise to self calculate my MPG and to keep my tires at 33 PSI to get better fuel eco, less weight in vehicle, and use cruise control as often as possible.

I keep things in my car but they aren't heavy. I drive some highway and more in town. I am not a heavy foot driver. I check my tires and do try to keep tires at 33 PSI n even when I don't check my tires PSI for a while ( when I was student and know nothing about cars) my dashboard had show an avg around 30MPG n haven't gone below 28 until now. I just haven't done the full tank to check my real MPG calculation. So overall, I don't understand and find it hard to accept that my dashboard avg, even if it isn't accurate, would suddenly tank to 23 MPG. I am not worry about the fuel but that there is a pinning issue with the car.

Have this happen to you? Do you have an explanation as to why the dashboard is doing this? The car computer?

 

You need to fill up the tank and from that do a bunch of driving - preferably highway - and figure out exactly what your fuel mileage is. As it stands you don't know if there is just some kind of instrumentation error or if you do indeed have some kind of a serious engine problem. Trying to speculate based on unknown information is pointless. What is your mileage?

 

mine has kinda done that too....its a 2015, ironically i replaced the starter also, because it failed, and the battery as a preventative item (8 years old)... i suspect its the fuel injectors on their way out (2015 has a warranty extension)..but if its runnin and driving...im more like....it is what it is...sadly ..

 

yep, i agree with woof. fill up, drive at least 40 miles, fill again to see how much gas you add, divide your miles by your gallons. reset the trip computer every time you do this so you can compare.

my money is on, the prior readout was cumulative over a long period of time, and after your battery replacement it was a new average starting in the winter months.

but you do need more info. just looking at the trip computer isn't telling you much, I'm afraid. 23 is low, but until you know if the display is accurate you don't know if you have an issue. you've replaced plugs and cleaned injectors and that's all a good start. make sure your engine air filter is changed regularly (given what your local mechanic did, I'd be very surprised if he didn't do that already). in fact, if your car is running well, no strange noises or smells, there's no codes, and the running gear is all in good condition, it's hard to say what is the culprit except guessing.

 

maybe try resetting the trip computer after a full tank? sometimes the readings can be off. not sure if it'll help, but worth a shot.

 

Current mileage is 74,441. I just got my car back from the dealership yesterday. I'll get back with the calculation when full tank is used up.

After I got my car back, this is bothering me - a constantly changing MPG. Usually, my car would update avg MPG after a while but it hasn't done update every few seconds or minutes. Yesterday when I got my car back, avg MPG is 26. The MPG would drop when I slow and brake, jump up when I accelerate, and in real time MPG drop as my car idle in the parking lot to it's lowest 18mpg. I texted the honda guy at the dealership and was told that is great because they had update software n advice me to drive on highway for 15 mins. I reset trip a and b and saw that the MPG went to "--.--" which I assume was an indication of 0 MPG. I drove on the highway for 30 minutes. I was able to get the MPG up to 32.5 but the MPG would constantly change. My last drive yesterday was showing a 30 MPG. My car has never done this before. From 2022-2023, my car maintain a steady 30 avg even after I reset my trip a and b. Can a software update make such a big change like this? Or is this normal and I just miss out?