poor mpg, should I be worried?

tescofan

hi, I've had my suzuki swift petrol 1.2L auto for about 8 months and the fuel consumption has been disappointing. On my regular 23 mile commute from the centre of Leeds to Huddersfield Royal Infirmary, I get at best 33mpg and this is usually with little traffic and 80% of the journey on the M62. I understand I'll never get the stated 55mpg but 33mpg on mostly motorways is quite terrible isn't it? I'm not heavy footed either, and stick to 65-70mph most of the way.

it's even worse in intra-Leeds journeys at 22 mpg. These are my own manual calculations done by me. I inflate my tyres once a month as well. Just wondering if this is poor or quite normal. thanks!

forgotmyname

Checking your tyres should be a weekly thing, not monthly.

33mpg for a 1.2 that does decent runs = something wrong.

Are you working it out properly?

Fill it up and run it down, then see how much fuel it takes to fill it up again.

Is it the 4x4 version?

tescofan

forgotmyname wrote: »

Checking your tyres should be a weekly thing, not monthly.

33mpg for a 1.2 that does decent runs = something wrong.

Are you working it out properly?

Fill it up and run it down, then see how much fuel it takes to fill it up again.

Is it the 4x4 version?

(odo now-odo last pump)/(number of litres) is how I calculate. Trip computer shows average 45MPG but that's obviously wrong. it's a 61 plate 1.2L FWD. what could be wrong assuming the tyres are properly inflated? (41psi front, 33 psi back as the recommended Eco pressure from suzuki)

PS. I've always assumed that the low mpg is cos it's an old fashioned four speed TC auto.

arcon5

I'd be interested in seeing emissions readings. MPG on a 4yr old 1.2L engine sounds awful. I get 44mpg from a 15 year old petrol focus with a 1.6L engine

agrinnall

The calculation is right (assuming you then convert from litres to gallons correctly) as long as you are filling to the same point each time, I've never been very sure whether the pump cut-off happens at different points depending on how the pump is set.

However, the answer is probably in your PS.

forgotmyname

Give an example of one of your calculations.

If the trip says 45 and your only getting 33, it sounds like something is not right.

AdrianC

tescofan wrote: »

Trip computer shows average 45MPG but that's obviously wrong.

Hmm. In that case, I'd probably say "Show your working!". The most likely cause for an arithmetic error is using the US gallon conversion (3.8 liters) rather than the Imperial gallon figure (4.5 litres) - and that wouldn't leave you very far off the difference from the trip computer figure that you seem to have.

Would you be prepared to post your log of fuel fills versus mileage, preferably extending over several fills?

PS. I've always assumed that the low mpg is cos it's an old fashioned four speed TC auto.

It certainly won't help. There's not a lot of power there to start with, and the torque converter will sap a good chunk of it.

Parkers gives book of 50mpg for the 1.2 auto, a bit worse than the 56 for the manual. They also give the autobox as one of their "cons" for the Swift.
http://www.parkers.co.uk/cars/reviews/facts-and-figures/suzuki/swift/hatchback-2010/49140/

Poor urban figure? Unsurprised. Especially if that's cold starts and short runs.

tescofan

here goes:
ODO last pump: 21503
ODO Now: 21707
Last Pump Vol: 23.7 Litres
204mi/23.7 = 8.61 mi/L

google "8.61 mi/L to mpg" to get 32.6mpg

AdrianC

23 litres per fill? You're multiplying errors with such small fill-ups, for a start. It's a 42 litre tank, use all of it. Measure it over a much longer period for greater accuracy.

And, yes, you're using the wrong litres/gallon conversion - 4.5 litres per gallon except in the US, so that's 38.7mpg straight off.

DUTR

tescofan wrote: »

here goes:
ODO last pump: 21503
ODO Now: 21707
Last Pump Vol: 23.7 Litres
204mi/23.7 = 8.61 mi/L

google "8.61 mi/L to mpg" to get 32.6mpg

21707-21503=204 miles
23.7L/4.54 =5.22 gallons
204/5.22=39.08 mpg

tescofan

the last 23L pump was to get the promotional 250 shell points, I normally get the full tanks anyway and they're not far off that mark.

Ah, so that's almost 40mpg then! How stupid of me, relying on google!! thanks all!