[ekudamram]

Bought a '99 (V reg) 1.2 Clio Grande, it drives very well, it's nippy and overall I think it's a really good car. My one problem with it though, is the appalling fuel economy. Before driving it back, I put £10 in the tank, set the odometer to 0, and drove back on the motorway, I drove economically, with a light right foot, kept the revs at around 2,000 rpm, however, I only managed to get 27mpg, now this to me doesn't seem right.

What could possibly be causing this? Does anyone have any ideas?

Cheers

[Rufusw5]

Probably a dodgy sensor or something, you need to take it to a garage and have it diagnosed properly using electronic diagnostics equipment. Otherwise you're just guessing..

[CurlyBen]

How have you worked out the fuel economy? The accurate way to do it is to brim the tank, just using the fuel gauge won't give you a meaningful reading. Otherwise you've got a bit of a problem.

[M4LLY]

Take it to the garage

[ekudamram]

Is it easily/relatively cheaply fixed?

[rmhumphries]

(Original post by ekudamram)
Is it easily/relatively cheaply fixed?

Depends what the problem is. Some things such as the air filter will cost you about a tenner to do yourself, so £20-£50 at a garage. Some things, such as a hole in the exhaust will be much more expensive.

[JC.]

27mpg eh? My 3.5 V8 can just about do that on a motorway.

The silly electronic readouts won't give you anything meaningful. My old jag used to have one. It recconed I was getting 99mpg down a hill!

[CurlyBen]

(Original post by rmhumphries)
At least one user suggested a fix, another said to take it to the garage. Both of these could have an estimate of a price attached, even if it is a range (£30-£200 for instance).

Not to mention that the poster who gave a stupid reply is the one who also made an earlier reply which could have a estimate price.

Where? Suggesting a sensor fault isn't a fix, and without knowing which sensor is faulty you can't make any sensible kind of estimate. I'm not sure "Take it to the garage" really constitutes a solution with a price tag attached either.
The OP hasn't even said how he established this figure of 27mpg, so it's not that surprising the answers aren't all helpful.

[ekudamram]

I set my odometer to 0, and drove around. After using 3 gallons of fuel, I had only driven 83 miles, and most of this was motorway driving

[mphysical]

This is not how you measure fuel economy.
The small volume and low mileage creates an unacceptable error.
It is best to ignore this and do the job properly

[CurlyBen]

(Original post by ekudamram)
I set my odometer to 0, and drove around. After using 3 gallons of fuel, I had only driven 83 miles, and most of this was motorway driving

But how did you measure 3 gallons? As I said before, the fuel gauge is nowhere near accurate enough to measure fuel economy.

[JC.]

(Original post by CurlyBen)
But how did you measure 3 gallons? As I said before, the fuel gauge is nowhere near accurate enough to measure fuel economy.

Quite.
One of our cars will do 150 odd miles on the first 1/4 of a tank according to the fuel guage. Then the next 70 miles (again if you believe the fuel guage) use up 3/4 of a tank!

The ONLY way to do this propperly is, as has been posted higher in the thread, fill it to the brim, drive about a bit and then fill it again.

Chances are it's probably perfectly fine.

[mackemforever]

(Original post by ekudamram)
I set my odometer to 0, and drove around. After using 3 gallons of fuel, I had only driven 83 miles, and most of this was motorway driving

What you need to do to find our your economy is as follows:

1) Fill your tank, absolutely to the brim.
2) Set your odometer to 0.
3) Drive normally until your tank is almost empty.
4) Fill it up again, right the top top once more, and make a note of how many miles you had done at that point and how much fuel it took to fill your car again.
5) Use those two figures to calculate your economy.

[CurlyBen]

(Original post by mackemforever)
What you need to do to find our your economy is as follows:

1) Fill your tank, absolutely to the brim.
2) Set your odometer to 0.
3) Drive normally until your tank is almost empty.
4) Fill it up again, right the top top once more, and make a note of how many miles you had done at that point and how much fuel it took to fill your car again.
5) Use those two figures to calculate your economy.

This is definitely the way to do it, but even this won't give an entirely accurate result every time as different pumps cut off at slightly different levels (and it's even affected by the speed the fuel goes in!).

[rmhumphries]

(Original post by CurlyBen)
This is definitely the way to do it, but even this won't give an entirely accurate result every time as different pumps cut off at slightly different levels (and it's even affected by the speed the fuel goes in!).

The error of what I imagine is in the region of 1L isn't significant if you are filling ~50L through, if you did 500 miles, then filling 50L gives you 10miles /L, 51L gives you 9.8 miles/L, 49L gives you 10.2miles/L. So your fuel efficiency will be accurate to with +-0.5miles / Litre, and the type of driving you do / weight in the car / etc will affect your efficiency more than that error range.

[CurlyBen]

(Original post by rmhumphries)
The error of what I imagine is in the region of 1L isn't significant if you are filling ~50L through, if you did 500 miles, then filling 50L gives you 10miles /L, 51L gives you 9.8 miles/L, 49L gives you 10.2miles/L. So your fuel efficiency will be accurate to with +-0.5miles / Litre, and the type of driving you do / weight in the car / etc will affect your efficiency more than that error range.

Normally it's not enough to notice, I agree, but recently I was doing the same trip (250 miles or so, mostly motorway with a 20 miles A roads either end) almost every week so my fuel economy was pretty constant. One service station I stopped at had a VERY slow pump which put maybe 10 litres more in the tank and my MPG result went down about 5mpg. It's definitely the best method short of removing the fuel tank afterwards though (although some modern trip computers are very accurate too, as they work on pump pressure and injector opening times to calculate fuel consumption).

[Minardi]

Even the Defender can just scrape 30mpg on a run. As others have said, brim, calculate, etc.

[InconspicuousGuy]

if it's overfueling its usually a problem with a dirty MAF sensor under the hood, that would be my first port of call...can of carb cleaner for about 3/4 quid will do the job

[Kevmeister]

Besides the already discussed/suggested problems, and the inaccurate method of calculating your mpg, it could still be quite a few things.

The car may need a service - new plugs, oil/filter, air filter.

Also, driving with a 1.2 at 2k/rpm won't achieve the best mpg - peak torque won't be available at that point in a n/a petrol. You may very well be labouring the engine a tad.

If you open windows, use air-con, heated rear window etc etc, then your mpg will suffer.

[ThisIsTheLife]

(Original post by JC.)
27mpg eh? My 3.5 V8 can just about do that on a motorway.

The silly electronic readouts won't give you anything meaningful. My old jag used to have one. It recconed I was getting 99mpg down a hill!

You probably were getting more than that... assuming your entire journey was down such a hill, I'm sure you'd get a ridiculously high fuel economy. Mine cuts off at 99mpg too.