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Low MPG in 1.6 D 2nd Gen

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Hero_uk1:
Hi Guys

My cars giving me low mpg (39MPG) when driving round town, is this normal? On autotrader its showing as 53.3 mpg (urban), i know autotrader isn't very accurate but my figures are way off.

My cars had full service history, had oil, filter and air filter replaced 2 weeks ago but still still get low mpg.

Have checked caliper to see if they are sticking but they aren't.   Checked tyres for pressure and they seem fine (32psi all round).

What MPG are others getting in 2nd Gen mazda 3 1.6 Diesel?

Please help!

Ian345:
My Gen 2 1.6D (don't have any more) gave slightly better results - just over 40mpg around town and up to about 50mpg on a run.

Less than 40mpg around town in these high temperatures does seem a little low, but depends on your driving style and the traffic conditions.

Most cars will give no-where near the advertised mpg. HonestJohn truempg is a good place to look for some real data.

Hero_uk1:
Thanks for the reply Ian. I would say im not an aggressive driver and change gears when it displays on my screen.

red_imps_2003:
I'm afraid I don't know what my typical mpg is in my 2nd gen 1.6d, as my daily commute is two thirds motorway and we tend to use my wife's smaller (petrol) for weekend runarounds. 39mpg doesn't sound too far off what it 'should' be, though, from my more casual observations.

How are you determining that figure, incidentally? Are you going off the on board display or using the brim-to-brim method? The latter is generally more accurate. Also, over what period of time? Have you just been measuring ad hoc journeys or was it over a more extended period of time? I would venture that urban journeys are more prone to fluctuations in mpg than regular stints on the motorway. As well as the tyre pressures already mentioned and the things you have already ruled out, how much weight you are carrying in your car (including passengers) can make a difference.

For what it's worth, my car typically averages mid-to-high fifties at the moment but, as I say, that is predominantly motorway miles and I drive very much with economy in mind over performance. The figure drops substantially during holidays when I do more driving around town.

If you are doing mainly urban miles, as it sounds, then you will need to be mindful of your DPF. It may not be getting much opportunity to regenerate (burning off the accumulated particles it has trapped) and risks becoming blocked. It may be worth sticking the odd bottle of Wynns or Millers DPF cleaner in and taking it for the odd 20-mile round trip on the motorway if that is not part of your regular routine. I also put a dose of Millers Diesel Power EcoMax (about £15 in Halfords or from Amazon) in the tank every couple of refills, which 'feels' as though it makes things run more smoothly.

It could be worth investing in a cheapy OBDII reader and downloading one of the many free sensor/fault code apps to see if anything pops up to give you further clues. I bought the one at https://www.amazon.co.uk/gp/product/B01N30RQNH/ref=oh_aui_bia_detailpage_o04_s00?ie=UTF8&psc=1 and the 'Torque Lite' app, which seem to do the job for less than a tenner.

Engineer Andy:

--- Quote from: Hero_uk1 on July 27, 2018, 10:06:02 AM ---Thanks for the reply Ian. I would say im not an aggressive driver and change gears when it displays on my screen.

--- End quote ---

You might find that the continuously very hot weather means that the mpg suffers because the A/C is not on 'eco' mode and is drawing more electrical energy and, as a consequence, fuel.  I just checked my mpg for my annual holiday down in the West Country and found that it was 'only' 39mpg, including two long runs of around 300 miles on the motorways, whereas when I've been (same place) in early-mid September, my car's averaged about 42-44mpg, so about a 10-15% reduction, probably because the external temperature was that much lower and the A/C didn't have to work so hard.  The traffic was about the same under both circumstances.  See what happens this week as temperatures are generally 5-7degC lower than the last week or so.

I would also check some of the go-to systems that can get clogged (DPF, CAT and EGR) - it may be worth buying some additives/cleaners, but also I would actually check to see IF the service work was actually done - another forum member reported (at my local dealer as well) that some of the consumables weren't replaced at the service despite being charged.  As you'll read on the forum, the quality of the service depts can vary considerably from dealer to dealer, compared to makes like Honda and Toyota.  Even more so an indies.

I suspect that you may find multiple causes, e.g. the A/C reducing it a bit and one or more of the other components mentioned needing a clean of some sorts, possibly coupled with a decent length drive and an Italian tune-up.  Bear in mind that a) 39mpg from urban only driving (even if using the brim-to-brim method) isn't that bad, especially if traffic levels are really high (I normally get 33-35mpg on that sort of journey with my 1.6 petrol) and b) the calculation method can make a decent amount of difference to the figure.  Trip computers aren't that accurate, though they are improving - nor can sat nav info be relied upon for mileage as it doesn't really know (and this take into account) differences in terrain (i.e. when you're going up and downhill), especially older systems.

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