Fuel consumption suddenly dropped

[rainbow-walker]

Not sure if this is the correct place for this posting, but anyway...

My 1.4(8v) Fabia normally does about 38mpg (the readout shows about 45mpg), and it has suddenly dropped to about 38mpg (readout showing about 28).

Its recently had its 60K service, with new front brakes, and I have also had two new front tyres fitted, and moved front wheels to back. I cant hear anything binding, and do about 80 miles per day, but the fuel consumption drop seems to be since the service (driving in a similar fashion of course).

Any ideas on what to check ? e.g. if they had put the air filter back badly could this have affected it ?

The engine note seems to have changed slightly, a little bit harsher - but cant be certain - could it just be coincidence and the engine is getting tired at 60k ?

Looking for any help or advice, what with this and the suspension problem (see Ask a tech section), I think this is the cars punishment for me looking at new cars !

Cheers,

RBW.

[A Laws]

I have a VRS and mine has dropped since it's November service.

At this time i got new tyres, which I think have contributed to the drop, however I feel the major cause is the temperature.

The average outside temp has dropped, to the point where the radiator never really gets hot, and the camshaft cover is only warm even after a 30 mile drive.

The ECU seems to be compensating for the colder engine by inducing more fuel, hence the reduction in fuel efficiency.

[rainbow-walker]

Ahh, now that would make sense, mine is petrol but I assume the argument is the same...

Thanks for the reply. I think the sensible option is to leave it for a few weeks and see if it improves.

Cheers.

RBW.

[A Laws]

Mine droped from 53 to 40mpg, and i was pretty annoyed to be honest.

To increase the temp a bit i've blanked off the lower grill, thus only allowing the bonnet grill to let air into the engine.

It seems to have worked a bit, my mpg has got better by 3mpg.

You can't win, this weather gives the ultimate performance for the car, yet the worst economy.

[rainbow-walker]

Does that apply to both diesel and petrol ?

[A Laws]

yep.

the ecu will add slightly more fuel to compensate for the cold.

People actually sell a 'Performance Mod' on Ebay which goes inline between the temperature sensor and ECU.

This is just a resistor, which fools the ECU into thinking it's colder, and hence pumps in slightly more fuel and supposidly increasing the performance.

So yes, the cold will cause your ECU to Pump in more fuel.

Going back a few years now, every winter we used to make up blanking panels to cover part of the radiator. - This would reduce the cooling effect of the radiator, allowing the engine to retain more of it's heat.

Rather than do this on the fabia, I just cut up an old rubber floor mat and tie wrapped it to the inside of the lower bumper grill to blank it off. This reduces the forward airflow over the radiator (and Engine) by half.

Theoretically you can blank off more, just make sure you don't blank off the air inlet pipe.

Try it......If it doesn't work you can always take it off.

[MagicBoy]

Have you checked the tyre pressures? My MPG dropped by 7mpg earlier in the week - checked the tyres and one of the rears looked slightly soft. Got the guage out and it was at 7psi! Pumped it back up and fuel consumption is back to normal.

[rainbow-walker]

Well, I dont feel so bad about the consumption dropping now, thanks guys.... MagiBoy, thats a good point as I had two new tyres a week or so ago, and havent checked the pressures since so they might have 'settled' a little.

I'll check the tyres tomorrow, and then give it a few weeks and see what happens.

Cheers.

RBW

[Tom_vRS]

My mpg dropped by 5-10mpg back in November. I put it down to the temperature, and 2 new Pirelli P Zero Nero tyres...

Tyre pressures do make a difference to mpg too.

[skidude]

I too have noticed a drop in mpg but I put it down to the extra 5 mins+ of engine idling whilst I scraping the ice off the windows!!!

Why am I here? It's New Years Eve for god's sake!

Happy New Year!!!

[Skodarulez]

Yup, take a look at the tyres. on my Octy I had 2 new tyres put on at the last service and checked the pressures about a week later, found that they were both at 24psi when I normallly do 32-34 at the front. Don't know why the (mobile) tyre fitter didn't put in more air.

[Skodarulez]

Why am I here? It's New Years Eve for god's sake! QUOTE]

It ain't a problem, man, not all of us are obsessed with the change of year. I'm switching off the machine in a minute and going to bed (only to be woken up by the fireworks at midnight.........)