What could cause lower than expected MPG [mechanically]?
 

Hey folks! After being car-free for three years, we picked up an '09 Honda Fit Sport AT. I used to have an '07 Fit Sport MT back in 2010, and got 42 MPG in that puppy without trying. Before I even knew about hypermiling.

Now, however, we've got a new-to-us Fit with 121,000 miles. It's the automatic with the select shift. I always use the select shift and I'm the main driver. Most P&G is done engine-on, mostly because I'm worried about using the ignition that much (since you can't bump-start), and because bump-starting is much safer in terms of reaction timing in case you need to act quickly.

That said, I still think I should be getting much better mileage than currently. I've only averaging 30, and the most recent fill-up was 350 miles of all 50-60 MPH roads, barely any traffic, barely any hill-climbing, etc. The fuel efficiency gauge on the dash projected 41 MPG, and from what I know of my previous Fit, it was very accurate. Unfortunately, I got almost 6 MPG less than that, and that seems to be the trend in this vehicle.

Therefore, I'm looking at mechanical reasons for this discrepancy. I've changed out the coolant, AT fluid and air filter, and replaced spark plugs. The transmission shifts like *butter* now. In a couple weeks, I'm changing the oil and filter, but they're not in bad shape now anyways. Tires on all tanks except this last one were at 29.5 PSI all-around. The sidewall says 51 PSI max, so I filled up to 45. I was really hoping that'd get me into the 40's. Bummer.

I do think that the valve clearance needs adjusting, but the car isn't idling strangely or anything, so it's not a top priority. I do need to do it soon, though.

I know that the 2nd gen Fit isn't as efficient as the 1st gen, but still.

Any thoughts?

The usual stuff.
MAF may be dirty or worn, oxygen sensor wear and need to be replaced, remove roof rack if you have one, add low rolling resistance tires.

It seems like the automatic Fit gets much lower fuel economy than the manual. Ecky can speak into it more with his S/O's Fit, but IIRC manual vs automatic is something like 10 mpg difference?

I'll add brake drag, wheel bearing and alignment.

My XFE had a evap solenoid go bad that was causing the Fuel Trims to max out taking it from 40 mpg down to low 30's, (essential a big vacuum leak) but it would run bad too, rich miss fire at low loads. Replaced $300 worth of other parts till unplugging the electrical connection to it and it returned to nomal. Replaced it yesterday for $32 CEL for it being disconnect hasn't cleared yet waiting to see if it will go away on it's own.

Edit: My CEL cleared it's self today.

Good point.
How are the tires wearing?
Brake drag is easy to diagnose at least and usually pretty easy to fix.

Toyota Rav4 do the same thing. The sticks get 30 something and the automatics are in the teens.

These have always been the issues I discover on used cars. Wheel bearings won't directly affect mpg but as they continue to fail they can cause an alignment issue.

Good call.

There is some front brake rubbing noise at low speeds. There's also a sway bar end link (I think) that needs replaced.

I've never worked on brakes before, so should be fun!

Tire wear seems fine, but they're relatively newer tires. Previous owners installed them just a few thousand miles before I purchased it.

The question is were they replace to hide something.:eek:

Go get a cheap tire depth gauge. Even with only a thousand or so they will still indicate uneven wear

if your only avg 30 your only doing slightly better then my 6.0 liter v8 hybird which is getting 25 on the highway... :D

Looks like your getting the correct MPG
Model: 2009 Honda Fit 1.5l
MPG: 27 city / 33 highway

Model: 2007 Honda Fit manual 1.5l
MPG: 33 city / 38 highway


they increase the size and different engine hence less MPG

Needs a baseline:

Top off fuel at an Interstate fuel station near home. Early on a weekend morning.

Fill slow to first automatic cutoff. Ease onto Interstate ramp and engage cruise control just below 60-mph before entering main lane. Travel 100-miles outbound, and using a pre-planned exit and crossover with no stops, return to that pump in the same way.

Refill at same pump in same way.

This test can be replicated by anyone. At any time. Only temperature and traffic volume differ.

Remember: cruise control ONLY. This IS NOT about highest possible MPG number. It’s the baseline for all other comparisons.

As you make this drive note instant mpg. In the future, any changes will show themselves here. There’ll be a high on this device, and you’ll have the trip Average. These are for comparison purposes.

As example, I “know” my pickup can be loaded to just over 1,000-lbs above TARE, and, at 59-mph/1,725-rpm I won’t EVER fall below 24-mpg despite weather, traffic volume or other extraneous condition. Over my initial period of familiarity (the first 10k Miles for anyone), I adjusted myself to what the truck wanted. So that 24-mpg is dependent. It’s my adjusted baseline for the South Central United States.

An empty vehicle save driver isn’t a test. The test comes with a load. As against the empty baseline, how does it fare?

A plan has these elements. Be inclusive. Downhill mpg in an empty car is meaningless by itself.

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Some responses are noting that the AT gets less than the MT, and you're noting that I'm getting the EPA estimate. However, both of these comments disregard that I am not driving under EPA testing conditions. If I were, I would get somewhere around 25 MPG combined instead of 30.

I believe the trip MPG estimate on the dash to be fairly accurate in these vehicles, and trust that the vehicle should be getting at least what the estimate says.

I think I understand. Take a 100 mile trip directly from a fuel station next to the interstate. Travel another 100 miles back to the same fuel station. Cruise at 59 the whole way. This is my baseline.

I'm not sure what you mean about after that though?

We weren't saying that the AT is rated lower than the MT - if I remember correctly, the AT is rated higher than the MT in the EPA tests. However, in real world eco-driving, the MT will get much better fuel economy than the AT.

A vehicle is designed for a load. How well does it do (have you learned) once it’s loaded?

There’s all the time in the world to learn when things are easy. Not so when they aren’t.

Empty MPG is a baseline against which Loaded MPG is compared. Sort of like highway against city. Takes practice to do it well. In turn, that practice leads to accurate prediction.

What’s the initial spread? What’s the percentage reduction possible? How is route-planning affected? Etc. Driving around empty is like jacking off.

When your family is aboard, and luggage-laden, is not the time to explore the differences. It’s too late.

It’s funny to see many here confuse frequency of vehicle condition (empty or laden) with importance.

Next to nothing is as unimportant as empty vehicle MPG. Vehicle specification AND operation have to work together when it counts. That’s when loaded.

Empty solo is covered by reduction of annual miles to achieve the same ends. The percentage change. The baseline numbers are just a control, they have no meaning in themselves. That’s vehicle weight or mpg when empty. Numbers baked-in at purchase.

It’s only when loaded, that counts. Tire life, brake life and “the life” of a gallon of fuel. Pretty much equal importance in evaluation. They’re confirmation. One can’t sacrifice longevity or reliability (or utility, IMO) to enhance MPG and ever argue “Economy” with a straight face.

The relation of Average MPG & Average MPH is key. The latter tends to predict the former.

It’s possible to greatly reduce the discrepancy between highway MPG and city MPG only. Same between empty & loaded.

Only loaded MPG matters. Empty mpg brags = paint color choice brags. Anyone can do it (defined course with cruise control). Loaded, city or highway is another matter. Percentage reduction between highway & city is the game.

Maximum utility would be loaded, and towing a trailer. As that second vehicle is a separate discussion, nonetheless it points us towards what is possible with just a gallon of fuel. Weight, and aero.

So, there’s a beginning. And an end. A framework. Not just what someone pulls out of their hind end.

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This is my exact experience with the 07-08 Fit, yes.

Different drivers, but my SO is regularly getting 45-49mpg in her 07 manual Fit, whereas my brother averages just about EPA in his 08 automatic - low 30's. The auto has much better top gearing than the manual, so it's not intuitive to me why this is.

Here's my guess: the auto seems to hold onto gears much longer - she shifts somewhere around 1500-2000rpm - and I expect the torque converter isn't locked up all the much in the auto.

Have him read Percent of Engine Load via an easily read gauge. You do the same.

Thirty plus years ago, I got thrown for a loop, tho. I had a mechanic look for why my car engine ran unevenly & gave low MPG. Cost me $300 & he still didn't solve the problem. I never thought it was the brakes, because the car seemed to coast pretty good, while in neutral. Eventually, the coast-down DID become more so. I went to Les Schwab for what I thought was an unrelated brake problem. At the time, while other mechanics wanted $300, Les Schwab did it for $160. My new brakes were wonderful, AND the engine ran evenly, with good MPG. Yeah, I didn't see that coming...... & neither did my first mechanic.

URabbit, do you know what your coolant temp is cruising on the highway? I don’t care what the gauge looks like, I’m looking for a digital number from a scanner / code reader / scangauge, or if there is a digital readout in a driver information center.

If you’re running slightly cooler than you should, there won’t be many symptoms. You would have reduced heater performance and fuel economy, but either of these could be minor enough a lot of people wouldn’t notice