Yeah, my CEL lights all work and are good.

 

I've just remembered that your Fit is only rated at 31 mpg combined (35 hwy and 28 city). Here's the EPA ratings:
https://www.fueleconomy.gov/feg/bymo...onda_Fit.shtml

The EPA ratings are done in a lab under ideal conditions, so not wind/air drag, no cargo, without electrical load on the alternator (music, AC, lights, GPS). The hwy rating is likely based on driving at a steady 55-60 mph (100 km/h).

In city driving (depending on actual traffic and how short the trips are), 25 mpg doesn't sound out of line at all.

Also for your 4 x 3 hr highway trips, you should have noticed much higher mpg (at least in the low 30's mpg range) if you drove the car under ideal conditions:
* no other passengers (especially heavy ones ) and no cargo. The impact of weight is 1-2% extra fuel for every extra 100 lbs (you need to account your own weight here too). So if you pack the Fit to it's max rated capacity of 850 lbs (including all passengers & cargo) this will reduce the mpg by at least 8.5% and up to 17% versus EPA.
* no fast driving (any 10 mph you drive over 50 mph tends to reduce your mpg by 10%), so driving at 80 mph burns up to 30% more than driving at 50 mph. 45-50 mph tends to be the ideal sweet spot for most passenger cars to hit their max mpg.
* no hills (since you burn more fuel climbing the hills than you save when going down them)
* no cold weather (cold air being denser than hot air, so it's literally harder to drive through it).
* properly inflated tires (at least 32 PSI when cold). You mentioned your tires were around 32 PSI. Did you measure them when before, or after driving? Even if you measure the tires "cold", but it's a warmer day, that pressure will drop when the weather cools.

 

I think Honda would tell you that 28mpg is not totally abnormal for winter. You are only a few MPG under the EPA estimate, and many people will run under it.

If you were getting less than 20mpg, I would say something is wrong enough to look more in depth. At 28mpg, it's unlikely anything is that bad. Emissions, timing, fuel problems tend to tank MPG even if something relatively minor has failed. I think you are OK to wait until spring and see if it gets better. Or if in the mean time things get worse or you get noises, smoke etc, then that would be a good indicator to bring it in.

Don't suppose you "warm up" the car at all before driving .. I don't think this has been asked yet. I do, when <10F. It takes a toll on MPG.

 

Stick with NGK plugs - you may want to replace coils too (if you do go with OEM coils). Replacing coils can save you a lot of stress as the coils can fail without warning.

 

Can I admit I don't know what you mean by 'the coils'?

 

 

I'll have to look more into that. What would be the benefit gained, and rough cost?