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post #1 of 4 (permalink) Old 30th May 2007 Thread Starter
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Poor Fuel Economy???

Hi all

If I've posted this in the wrong section can somone please let me know.

Iím hoping someone can help me work out if I have a problem with my Lag II fuel economy.

Since buying the car in December 06 it consumes fuel much faster that I had expected for a 1.6L engine. It seems to guzzle like a 2.0L and itís not even a 1.8L!

Hereís one example of why Iím suspiciousÖ

On 10/05 I filled the tank, £56 (ouch!). On 27/05 I put another £15 in. This £71 provided with: x1 Nottingham Ė Birmingham return trip, x1 Nottingham Ė Leicester return trip, Mondays Ė Fridays to and from work (12 miles round trip) between 10/05 & today, and the odd trip to the local shops. The fuel gauge needle is now on the highest red line....again!

The Laguna has been fully serviced this year, done about 55,000 miles and is a 2001 plate. If you need more specs just ask.

To help you help me I thought Iíd reset my Lag II computer whilst on the M1 and take some readings. Here are the resultsÖ

Over a distance of 6 miles at a constant speed of 70-75mph at 3200rpm the computer displayed a maximum of 47mpg.

Now Iíve never had a car with a mpg reader so not sure what the norm is for my spec of car based on the above criteria. Should I be getting better mpg or is this ok???

Also, but even more concerning, after leaving the motorway and driving through towns/junctions/traffic lights etc the mpg counter sticks until reset. It then provides readings over the next 1-2 miles before it gets stuck once more. This happens all of the time. So, in light of this how do I know the counter is providing an accurate reading? Is it??? Can I rely on it???

I could go on and on but Iím sure Iíve said enough for someone to throw some suggestions at me.

Am I expecting too much in the way of fuel economy or do I have a problem?

Thank you all for reading and for any suggestions.

Currently in jamesleicester's garage:
Laguna II 1.6 Expression 2001
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post #2 of 4 (permalink) Old 30th May 2007
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Hi James.

I'm not entirely sure if you have a problem, but your computer doesn't (I believe) have an instant fuel readout - what you are looking at is the average MPG. This will change more readily at the earlier stages after being re-set, and then changes will start to slow down in frequency as time/distance elapses.

What I would suggest is to brim the tank - re-set the computer & trip counter, then drive as you would normally until your next fuel stop - note the miles you have travelled, and the litres needed to brim the tank - divide this sum by 4.54 to convert litres to gallons, then divide the miles covered by the gallons used - this will give an average MPG figure. Which can then be compared with the computer to assess its accuracy.

Don't use the brochure figures as a benchmark - they are based on laboratory conditions, but check simple things like your tyres are inflated correctly, and that you aren't carrying excess weight in the car or a roof rack. Also, take into account congestion and delays adding to the time spent idling in traffic.

Once you have your own definitive figures calculated, I'm sure you will be able to assess your car's health.

Hope that helps,


This job should never be complete - the day I think I've done it all, is the day I resign.

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post #3 of 4 (permalink) Old 30th May 2007
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As Vel says, you need to calculate what MPG your car does on a full tank, at least, nobody wants to get maps out and start calculating distances for you.

Having said that 47 MPG at 70-75 on a motorway is extremely good MPG for your car.

My Lag 11 1.8 does at least 38 MPG all the time over 1000 of miles driving.

A problem well stated is a problem half solved !
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Last edited by davesss; 30th May 2007 at 11:52 PM.
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post #4 of 4 (permalink) Old 31st May 2007 Thread Starter
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Paul / Davesss,

Thanks so much for your advise. I will brim the tank as suggested and see what MPG my car does using the suggested method.

Currently in jamesleicester's garage:
Laguna II 1.6 Expression 2001
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economy , fuel , poor

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