Mpg Puzzle
Author
Discussion

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
Here's an odd thing (or maybe not?)

The little Fiat Sedici I run (aka a Suzuki SX4 with the 1.6 107 bhp petrol engine also used in Swifts) is doing better mpg (37+ plays 35+) now that it's doing 2x3 miles per day stop start miles on the Rail Station run than it used to do when doing longer and more mixed journeys.

Puzzling - it has always returned between 35 and 35.5 mpg since I got it, regular as clockwork, so this is a noticeable improvement. I was expecting perhaps low 30s as it's got quite an aggressive auto choke on start up, and it barely gets warm by the time I'm parking either at home or at the station.

Maybe just the warmer weather, perhaps - what do you think? It also had an oil change to a full synth (from what I don't know) at about the time the last tank went in, so that might have had some modest effect, too?


fezst

257 posts

153 months

Tuesday 5th August 2014
quotequote all
This is pretty boring.. I mean it's 2mpg difference we are talking

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
Thanks for the input and taking the trouble to comment - it's very much appreciated.

trickywoo

14,164 posts

259 months

Tuesday 5th August 2014
quotequote all
107 horse in something that size probably meant that you were working it harder than you might think on the longer journeys.

Aerodynamics can't be that good either hence performing better on a short low speed run.

Your tyres might also be harder due to the hot weather.

TLandCruiser

2,877 posts

227 months

Tuesday 5th August 2014
quotequote all
Someone call Sherlock Holmes!

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
TLandCruiser said:
Someone call Sherlock Holmes!
I have - he says there's no chance of solving this one without lapsing into unconsciousn...

xRIEx

8,180 posts

177 months

Tuesday 5th August 2014
quotequote all
trickywoo said:
Your tyres might also be harder due to the hot weather.
I thought it was the other way round?

dave_s13

14,028 posts

298 months

Tuesday 5th August 2014
quotequote all
Get a pushbike or some trainers you lazy bstard.

dave_s13

14,028 posts

298 months

Tuesday 5th August 2014
quotequote all
xRIEx said:
trickywoo said:
Your tyres might also be harder due to the hot weather.
I thought it was the other way round?
Increase temp = Increase in pressure = "Harder" tyres???

donaircooleone

451 posts

206 months

Tuesday 5th August 2014
quotequote all
dave_s13 said:
Increase temp = Increase in pressure = "Harder" tyres???
I imagine the small increase from pressure is probably masked by the softened and slightly warmer compounds of the tyre.

xRIEx

8,180 posts

177 months

Tuesday 5th August 2014
quotequote all
dave_s13 said:
xRIEx said:
trickywoo said:
Your tyres might also be harder due to the hot weather.
I thought it was the other way round?
Increase temp = Increase in pressure = "Harder" tyres???
See what you mean, I automatically assumed rubber 'hardness'.

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
dave_s13 said:
Get a pushbike or some trainers you lazy bstard.
Funnily enough I bought another one yesterday, but I'm bludgered if it's going to be used for the station commute (more than once, given the chances of it still being there in the evening of the first day!)

I think an earlier poster's probably there or thereabouts given the nature of the engine which has a pretty high peak torque rpm (4k IIRC?) so enforced pootling at low rpm may just make that slight difference. Tyre pressures I adjust pretty regularly, so I'd discount that factor.

I was just surprised - first time by how uneconomical it was when I was doing journeys that I thought should have been so, and how relatively economical it was when I definitely hadn't expected it to be.

R6VED

1,491 posts

169 months

Tuesday 5th August 2014
quotequote all
fezst said:
This is pretty boring.. I mean it's 2mpg difference we are talking
Harsh but undoubtedly fair :-)

chris333

1,034 posts

268 months

Tuesday 5th August 2014
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chaps...why the hostility? This is a car related website. The OP had a valid question. I'm sure he was probably expecting the mpg to go down to 25-30 for the short trips (which would have been my guess).

If you just want to talk wheelmanship, fezzes and getting the back end out, there are plenty of other threads.

thatdude

2,660 posts

156 months

Tuesday 5th August 2014
quotequote all
It is quite odd, because my MPG drops in my civic (1.6, 110 hp) until the engine is warmed and off the cold running map. I should think if I was doing short trips every day that it would drop to below 40, instead of its current 47-48 (average range over 17,000 miles)

2 mpg can be easily accounted for by differant fuel (summer blends?) and better oil (changed it recently for something decent?)

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
chris333 said:
chaps...why the hostility? This is a car related website. The OP had a valid question. I'm sure he was probably expecting the mpg to go down to 25-30 for the short trips (which would have been my guess).

If you just want to talk wheelmanship, fezzes and getting the back end out, there are plenty of other threads.
I'm rather dull these days, I guess (Think Billy Bragg "Brickbats" wink) - certainly when compared to the days of fast cars and bludger the cost! I was however genuinely puzzled by this as it was counterintuitive to me and wanted to see what others thought

I did post with some slight trepidation, because of the proliferation of PBCDs on here, but hey, I'm old enough to take some ribbing. (Except perhaps from someone who has thus far contributed the square root of naff all to Pistonheads, perhaps smile)

Bonefish Blues

Original Poster:

36,519 posts

252 months

Tuesday 5th August 2014
quotequote all
thatdude said:
2 mpg can be easily accounted for by differant fuel (summer blends?) and better oil (changed it recently for something decent?)
Yes, absolutely, but combined with a dramatically different journey profile, I thought it odd that it still went the "wrong way".