Poor fuel economy? *Please read this!* (the *definitive* poor fuel economy topic)

[culzean]

changing to lower gears to increase engine braking before the box is ready to change down itself will put more energy into the gearbox, the energy of slowing the car has to go somewhere, either into the brakes as heat or to the gearbox components as ---, you guessed it as heat,  - you choose.  (one of the rules of thermodynamics is that all energy eventually ends up as heat).

[guest4288]

OK, so the CVT fluid or the components of the box may heat up, but does it follow that this will induce more wear?

[madasafish]

Heat  eventually degrades oil characteristics meaning wear will accelerate...

[Chris_Music]

I can't for the life of me work out why my current Jazz can't get as good MPG as my last Jazz, even though they are both the same model!

Old Jazz used to easily get between 55-60mpg from motorway driving and 45-50mpg from town driving (Jazz dial mpg readout).

Old Jazz was a 2005 Sport with 110,000 on the clock. The spark plugs needed changing, the oil was almost black, it basically needed a major service service. Front two tires were on about 2.5mm, rear were on about 6mm.
It had a K&N panel filter, but I don't think that would make a massive difference on the MPG, and it had been on there for about 30,000 miles. I even managed to get 73mpg out of it, travelling from Hertfordshire to North Wales and back on a full tank, nearly 550miles ! I always ran it on Shell VPower.

Poor Jazz got written off earlier this month !

New Jazz is a 2006 Sport with 70,000 on the clock. Car was getting 33mpg when I bought it, but it needed a major service and had a binding rear brake.
Car now has 4 new tyres, new oil, new oil filter, new standard air filter, new NGK spark plugs, new rear brake calliper, all brakes checked for binding and brake fluid flushed out and changed. I have been running it on VPower for 2 and half tanks now. Tyre pressures are all correct.
I am still struggling to get 50mpg or over out of the car driving on motorways, and barely got 180miles out of half a tank of fuel !
I can't think of anything else that could be affecting the MPG. I really don't think its the K&N filter on the old car, especially since I hadn't cleaned it out for 30k! And especially since the old one desperately needed a service and still got me 73mpg!

Can anyone think of anything else that I might have missed?

Cheeers!

[guest4218]

Hi i think is the weather and winter which are giving bad mpg i noticed with my Jazz in summer i was getting 55 mpg now is winter i get 50/51mpg and the only thing i chaanged was fitting 2 new falknes.

[Chris_Music]

Hi i think is the weather and winter which are giving bad mpg i noticed with my Jazz in summer i was getting 55 mpg now is winter i get 50/51mpg and the only thing i chaanged was fitting 2 new falknes.

Has the weather really changed that much in 4 weeks that would make the difference between an older/higher milage car that badly needed a service getting higher MPG in late October than a car thats just had a major service with everything changed in November? I never remember the cold really affecting my MPG that much the last two winters, maybe 2 or 3mpg!

[DV]

The cold weather would make up to 10% change in fuel consumption.
Check if the water temperature sensor wire has not got any resistor built in (the engine controller would think it`s even colder outside so more fuel would be injected for better performance = cheap tuning).
Is there any oil consumption? Checked tappets?

[guest1393]

Hi There,

In the winter my 04 drops from 43mpg to around 34 mpg on local journeys in the hills of West Yorkshire.

My wife in a 57 who only does short local journeys i.e. school runs drops from around 39mpg to around 31mpg. 

Cold engines and cold air through the intakes drops it terrably as does putting the heater n (hardly use the A/C in the Summer).

Regards,

Andrew

[Chris_Music]

I agree the cold weather affects the MPG, but the weather isn't winter cold yet. Its been 8-10 degrees at night and hasn't dropped below 0 degrees yet, still yet to get ice on my car!

[guest1844]

First suspect is always brakes binding even a tiny bit. I was surprised when I changed the front discs/pads on mine to get several mpg improvement. Just take the pads out, clean them up and put them back.

[peteo48]

On cleaning pads, when I had a VW, there was always an item on the service invoice for brake cleaner and I was told that they routinely cleaned the brakes. (whether they did or not I'll never know).

The other thing with the VW was the brake pads lasted at least 3 or 4 times as long as Honda ones do. This makes me think that Honda pads are made of a softer material and possibly the dust generated causes the brakes to bind?

Just a theory but the brake binding issue seems to crop up quite a lot on this site but also civinfo.com

[madasafish]

My fuel consumption -over the same journey and routes ahs dropped 8% in the last 3 weeks with colder weather. Happens every year.

[guest4492]

Hello

I have Honda Jazz SE sports 2003, 1.4 engine. I have noticed a significant drop in fuel efficiency from 39miles/gallon to 32.5 miles/gallon . There is no improvement even after full service last week including oil and filter changes and wheel alignment.Also, I get the car serviced every year. Either it could be because of poor car service or something else. Six months back, one of the main part of exhaust was replaced since it was quite corroded and wondering if it could have made a difference. Please advice.

Thanks
PK

[madasafish]

It's winter

[guest1521]

Winter...

http://www.theaa.com/motoring_advice/news/aa-fuel-for-thought-increased-cost-of-winter-motoring.html