Once you've checked your tyre pressures, it's most likely just the nature of the engine. As far as I know, Skyactivs are not turbocharged and better suited to constant speed than stopping and starting.

I suppose it really depends upon how short the trips are, though I suspect something else is going on here. I presume the brakes aren't been ridden either. Did you actually have the brakes checked by a mechanic to see if they were binding (stuck on shoe(s) and/or warped discs)?

I own a 1st generation Mazda3 1.6 petrol, and aside the the occasional 'Italian tuneup', my mpg has never dopped (over a run) below 34mpg, and that was in heavy traffic.

Your car on an average driving pattern (borne out by the data in HJ's 'Real MPG' section) should be averaging around the 45mpg mark, and likely around the high 30s in heavy traffic.

Obviously for using a car for just short trips to the shops will reduce that (and not do any non-EV any good at all) down to the low 30s because petrol cars will always use a rich mixture for the first few minutes upon a cold start, but to me, something seems off if you're only getting low 20s mpg out of it.

I take it you've done a 'brim-to-brim' mpg check rather than used the trip computer, most of which aren't that accurate?

A sensor of some kind may be giving a false reading for one reason or another and may need cleaning/clearing of debris or a faulty one replaced or a dodgy connection rectified. Not sure wheteher clogged fuel injectors would give that sort of problem, or at least to that degree.

If it was, it should be reasonably simple to clear it using (via the fuel tank) shop-bought injector cleaners, which are a decent, relatively alternative to using branded super unledaded. I'm also presuming that other people haven't experienced similar problems in your area - perhaps bad fuel?

Other than that, a check for fault codes via the OBD port might be worth it Just guessing on my part. Others here are more technically qualified on diagnosing such issues.

I'm currently getting around 32mpg average per tank mainly urban driving at the moment in my Mazda6 estate. In my last place of work which involved some A road driving, I averaged about 45mpg.

My urban commute is about 6 miles each way and isn’t overly congested thankfully, I tend to travel at quieter times (outside of the school run window). Short runs shouldn’t really be an issue, at this time of year, mine is warmed up within the first mile (start stop system kicks in when it is).

If in very heavy start stop traffic, I could probably expect to do a bit worse than I currently am, however 25 does seem on the low side. Might be worth rechecking that your brakes aren’t sticking a bit, strip them apart and regrease the pins, and also pump your tyre pressures up a bit. The pressures on the door jamb can be a little on the soft side so try adding an extra 2psi in. Also after a good long run in mine recently after many months of urban crawling, the engine is running like a metronome, so maybe a good thorough Italian tune-up is all you need. Get it nice and hot to burn of any carbon that my have built up on the inlet valves.

In comparison, my wife's CHR hybrid can exceed 70mpg on the days that i borrow it (just spotted your other thread). Even still, it would take many many miles of driving to make back the cost of changing car so I wouldn’t recommend you do so on a knee jerk.

What do you mean by a short trip? I can easily average 45 in my MX-5 1.5 Skyactiv-G (129bhp), and the those with the 2 litre cars say they get up to 5 mpg less. Unless you are literally driving a few hundred yards, it does sound as if there is something amiss even allowing that the MX-5 is probably 25% lighter.

Mine is currently showing an average of 40 on the current tank, over about 280 miles, but that includes 52 miles around Castle Combe circuit at just over 20mpg, so driving there and back worked out at about 50.

Skyactiv-G of that vintage do have a 'high' compression ratio by traditional standards. I've seen 13/14/15 in the spec for different applications.

Mazda chose this unforced induction strategy rather than turbos because in the real world it is more economical. Under the previous convention the mpg of some turbo petrol cars was 20% or more worse than the official combined figures. It does sound as if there is something not quite right.