Average MPG has dropped since service and MOT?

bill_the_bus

Had my car, 63 plate 1.0 ltr petrol Fiesta, in for a service last week and my average MPG has dropped considerably since getting it back. Have had it 3 months and drive the same 30 mile route to and from work and been averaging 57-58 MPG in that time, resetting a few times. Since the service it is gown to around 47 MPG. It was only in for a standard service but for some reason it had replacement spark plugs also, he says as the car has high mileage (58000) so may have needed them, had a major service last year so should have been replaced then. Any suggestions to why this may have happened or is this normal and maybe it will setyle down.

When daughter bought car 4 years ago it was bought as an eco boost but I cannot find anything to say it is so may be just the basic.

BoGoF

Has this coincided with the cold snap?

Cold weather affects your mpg.

forgotmyname

And im guessing your using the trip computer for the figures?

So the buyer before you did long steady runs and got a really high MPG figure. You bought it and even though you only average 47mpg the mileage you have done didnt make a dent in the AVERAGE mpg.

But at the service it was reset and now its showing an average of 47mpg which is exactly the same as you were getting before. Or the car sat in the workshop running for a little while doing zero MPG.

And then as mentioned the cold weather so your heaters and lights have been used more and takes longer to warm up which uses more fuel in the process.

wgl2014

I would double check some basic things, are your tyre pressures correct or brakes rubbing (I would hope not just after a service). Is the Aircon on when it was off before?
Also have a look and see what oil was used, modern engines run thin oil to maximize economy. Was the service done with a different grade to the last one? Have the correct spark plugs been used?
As others have stated the recent cold weather is likely to have impacted the economy, longer time to warm up and extra time sitting idling whilst your windows demist.

If after checking the above you are still concerned I would give the garage a call and see what they suggest.

droopsnoot

forgotmyname wrote: »

So the buyer before you did long steady runs and got a really high MPG figure. You bought it and even though you only average 47mpg the mileage you have done didnt make a dent in the AVERAGE mpg.

OP did say the reading was reset a few times during the three months.

facade

The real test is are you putting 20% more fuel in each week, to go the same distance?
My Renault Nee-San does 7 miles to the litre going to work, at the last fill up I had to put a couple more litres in than I expected, due to the cold weather, less than 10% more.

WobblyDog

In my 1.25 litre Fiesta the fuel consumption does worsen during the winter, hovering at around 46mpg. It's closer to 50mpg during the summer. I'd like to know why. I record fuel consumption carefully. I don't think it's entirely due to time taken to warm up the engine, because I don't make many short journeys.

BoGoF

https://www.holtsauto.com/redex/news/how-cold-temperatures-affect-car-fuel/

tykesi

WobblyDog wrote: »

In my 1.25 litre Fiesta the fuel consumption does worsen during the winter, hovering at around 46mpg. It's closer to 50mpg during the summer. I'd like to know why. I record fuel consumption carefully. I don't think it's entirely due to time taken to warm up the engine, because I don't make many short journeys.

So what else do you think it is?

My Civic averages 40-42 MPG in the summer and in the winter this drops to 34-36. This has been consistent over the five years I've owned it so what else do you think could cause this at certain times of the year, every year?

WobblyDog

tykesi wrote: »

So what else do you think it is?

My Civic averages 40-42 MPG in the summer and in the winter this drops to 34-36. This has been consistent over the five years I've owned it so what else do you think could cause this at certain times of the year, every year?

My fuel consumption spreadsheet also shows strong seasonal variation. My guesses as to the causes are as follows, but they are all just qualitative hand-waving, I wish someone would do some quantitative experiments and attach numbers to each factor:
1) Engine spends longer warming up at the start of each journey.
2) Engine never reaches optimum temperature, even on long journeys, because the engine cooling mechanisms are designed to cope with the hottest summer days, and can't be turned down low enough.
3) Increased electrical load due to headlamps and heater fan.
4) Increased rolling resistance on wet roads.
5) Increased rolling resistance of cold hard tyre rubber.
6) Increased air density causing greater aerodynamic drag.
7) Increased oil viscosity causing extra friction in engine.

System

10% drop in my Mondeo from November to around February.