Poor fuel economy from a diesel – does this sound right to you?

We own a Renault Megane GT DCi (150bhp), and with honest gentle driving at national speed limits are acheiving 42mpg.
This is a combination of motorway and urban driving. The stated economy for this car from various sources is 51mpg (up to 58mpg).
I have seen ‘real world’ figures mentioned on one site of 45mpg combined, but this was a slightly different model.

The car has only covered 23k, drives extremely smoothly and pulls well. From what I can tell there are no mechanical or fuelling problems or symptoms.

Should we be getting more or is this just a very disappointing turbo diesel with inflated mpg advertising?
What should I check for?

It doesnt sound much, but If it were acheiving 50mpg id be very happy with the car as a whole. As it stands, 40mpg is niggling away and persuading me to drop a load of cash and trade for something else.

I have a Magane Grand scenic with the 1.9dci engine.

I do most of my driving aroudn town and get less than 40mpg – I can get this up to 45-50 on mixed roads if I’m *really* careful with my right foot and drive for economy.

I think it’s not bad for a heavy car with a turbo engine, tbh – I used to struggle to get the right side of 30 on my Old School Saab 900 2.0 Turbo…

40 mpg is indeed poor.

You could look at your driving style. You need to get up to speed with middling acceleration and then hold as constant a speed as you can, then lifting off well before any traffic lights or roundabouts and coasting in. If you want to do even better lift off at every opportunity and just touch the throttle reeally gently so that you slow down very slowly. This can annoy drivers behind you though if you take the piss.

You don’t have to be slow in acceleration, but you do have to be really smooth and have a light touch, and use the accelerator and brake as little as possible once up to speed.

Some people don’t realise how they drive – I had a lift with a bloke who was always hard on all the pedals, regardless. Boot down, brake hard ALL THE TIME even on the motorway at overall perfectly reasonable speeds – he thought his driving was perfectly normal, I was almost sick in the passenger seat.

Also check tyre pressures.

Drive a 2litre Volvo V50 RDesign Diesel.

Consistently get between 50-55mpg combined – obviously bit more if a doing a long motorway drive.

Make of that what you will.

<edit> but then of course it is a Volvo so can’t have it all ways 😉

42 doesn’t sound unreasonable for urban driving, its about what we get from a VW 140bhp diesel.

one thing that is recommended with Renault Diesels is to really boot them every now and again – somethign to do with the emissions control stuff getting sooted up if you don’t get a bit of pressure going through the turbo and engine.

The suggested advice is that as a rule of thumb, take the stated economy figures and multiply by 75% to get to real world numbers.

Changing your car for the sake of 8mpg? A complete waste of time and money.

Blimey! my 140bhp VW does 50-55 urban/combined and 60 moterway and i’m not very timid!

42mpg is the best I can manage in ‘driving Miss Daisy’ mode. If I had my own way with the right pedal i’d be getting around 34mpg.. which is rubbish.

Im peeved as my 12 year old Golf estate Tdi (90bhp)was thrashed every day and never fell below 47mpg

If you are not doing many miles then it will automatically be poorer than ‘average’, and there is nothing like a modern TD for having a variation in mpg it seems.

And it is showing an Urban of 30mpg…

so your golf produce 40% less power and used 15% less fuel to do so?

sounds like the “diesel used:bhp” ratio shows a fairly frugal Renault engine?

42mpg on a 150hp car unreasonable? id say not to be honest, ive lost 2mpg since december to present with the cold mornings etc…

if you are driving steady 60mph roads then you should be getting more, but general driving duties in towns with plenty of stop/starting and traffic and life in general id say 40-45mpg on a 150 horsepower car was pretty reasonable?

wwaswas
one thing that is recommended with Renault Diesels is to really boot them every now and again – somethign to do with the emissions control stuff getting sooted up if you don’t get a bit of pressure going through the turbo and engine.

I’ll give that a go, we’ve not owned the car long and I know that it only covered 300 miles or so in the year leading up to us purchasing it, It has crossed my mind that it needs a good blast to loosen up.

Its in spotless condition for a 4 year old car, perhaps the previous owner drove slowly everywhere.

Audi A3 with PD130 engine in does an real average of ~39mpg.

it is the quattro though which loses a bit..

Passat estate with same engine in, driven the same on the same route does ~47mpg

so your golf produce 40% less power and used 15% less fuel to do so?

sounds like the “diesel used:bhp” ratio shows a fairly frugal Renault engine?

Well, when you put it like that…

But in defense, the Golf was ragged – whereas the Megane is being cosseted around, mainly changing gear at 2000rpm or less.

I did get 55 out of the golf when carefull with it. The figures wouldnt look so good on the Megane if I was heavy on the right pedal.

Now you mention “only did 300 miles in a year” that does suggest that the thingummy clogging up doodah might be an issue for you.

However from my detailed technical knowledge of the gunged up thingummy issue (read an article about a bloke who did sod all miles in his Jag diesel and complained that it had this problem) I’m afraid that giving it a blast at this stage won’t help – IIRC (and I may well not tbh) the giving-it-a-blast thing was to stop the problem occurring, and once the problem HAS occurred the solution involved replacing some expensive (in a Jag at least) bits.

There may be someone else with more knowledge on this than I….

2l volvo v70 diesel here..22k on the clock… as just about all my driving is round town now, I am only getting 32mpg 😥

This car will not be with me much longer 😆

Civic 2.2 Diesel, which is quoted at 54 mpg and over the last 2,800 miles has averaged 44.3 according to the on board computer.

Not Miss Daisey driving, but normal driving, not ragged everywhere!

have a look on the renault forums;

http://www.renaultforums.co.uk/showthread.php?t=111310

the EGR does seem to get blamed for poor economy.

Jeez, that’s poor I reckon.

I had a Megane dci estate as a hire car in Belgium a few years ago – original shape Megane. No idea what engine was in it, but from it’s performance, I reckon it had at least 100bhp, probably more..
I got 58mpg from that (computer indicated, admittedly) without even trying. Ratio of urban/motorway, probably 20/80.

My currentl 130bhp Ibiza diesel (1.9 VAG PD engine) does 55mpg when driven ‘normally’, nearer 60mpg when really being careful & the lowest I have seen was about 44mpg on a erm, spirited drive to Cornwall with two of us in it, 2 weeks of “pack the kitchen sink” camping gear and 2 bikes on the roof!

Many people just drive their cars around at low rpm. They need a bit of exercise!

Give the car an Italian tune-up (warm it up and drive along in low gear at high rpm for a sustained period, using plenty of welly), it can work wonders.

The more expensive alternative is a German tune-up, which involves driving flat-out down the autobahn as much as possible, which can produce also excellent results and a nice holiday.

Change the air filter, clean the air-flow meter and clean the EGR system.

Be happy with around 50mpg on a run, but don’t be expecting miracles.

so your golf produce 40% less power and used 15% less fuel to do so?

No.. the 90 or 140bhp figure is the MAXIMUM bhp. When driving along the amount of bhp you need to maintain a steady speed on the flat depends on the aerodynamics and the tyres. That’s why vans are less economical than cars.

The 45mpg or whatever figure is not achieved at max power 🙂

Clogging is a distinct possibility if it’s been babied. I do think 42mpg is poor though – my Passat is bigger and auto and I can easily get 42mpg around town, about 38 if I am in really heavy traffic mind.

Urban driving, short journeys (< 4 miles) and cold weather have killed the economy on mine to around 40mpg. (150bhp cdti, probably the same engine)

In the summer i’ve had 62mpg out of the entire tank driving at around 60mph on motorways.

I think it just depends how its used.

Theres lots of people complaining they don’t get the manufacturers figures, i think they’ve got better at optimising the cars for the economy tests.

Our Golf 2.0 GT (with 100k on the clock) over the last two years has returned an average of 43mpg over 25k. Driving is 80% shortish trips on country lanes and I don’t think this is too bad.
Last year I used it to do a 60 mile motorway commute into Manchester (so plenty of queuing for the last 2 miles in) for 2-3 weeks and the best I got was about 58mpg average for one of the trips back home – I was driving fairly softly at about 70mph on the motorway.

I have a 100bhp Megane Diesel and I average 65mpg on the computer.

I do however drive like an old man, I do no more than 70mph on the motorways, I coast a lot, I brake only when I have to and accelerate smoothly and slowly. I also do the above mentioned Italian Tune once a month to keep everything soot free and running smoothly.

Octavia 1.9 trial 90bhp here. 80% motorways and keep air on off with tyres checked regularly. easily get 60mpg over a tank.

I do all the above with driving style and giving it a run at high revs etc. However, I am known to drive like an old person 🙂

Given that many car speedos are close to 10% over reading does this mean that the odometer is also over reading the distance by nearly 10% making these quoted real life MPGs better than they are in reality?

The MPG displays in vehicles are indicative only of what you are doing at that particular time. To find the true mpg of a car you need to track the mileage against the actual fuel consumption. there’s a good app called Road Trip that tracks your mileage and fuel costs and calculates your actual mpg.

For example.. Octavia 1.9 = 14gallon tank.
@60mpg = 840 miles per fill. call it 820 from full to flashing fuel light. Are you getting near to that on a full tank?

One of the problems with comparisons is what defines ‘urban’. If it involves lots of stop start, waiting in queues, trafic hold ups then consumption will be a lot less than the ‘urban’ quoted figs. My commute is often very much the former, taking 45 mins plus to go 7 miles. If the weather is cold/dark/damp and lights, heaters etc on then my ‘average’ consumption on this ‘urban’ route is 34mpg. On an ‘urban’ drive when roads are clearer then i get 45, and on a longer drive then i get 55 plus. 2010 BMW 318d with stop start etc and a lightish right foot.

The MPG displays in vehicles are indicative only of what you are doing at that particular time

Unless you use the average function…. now it may not be accurate of course, but remember also that petrol pumps do not always shut off at the same point so brim-to-brim only works over several tanks.

I have the 175BHP version of your engine in my Megane.

Don’t panic – it is about right!

I now consistently get 38MPG from a mix of town and motorway driving.

What I found with mine was that it didn’t really loosen up and start producing decent figures until about 35k miles. There was an improvement of about 20% at this point…

Hope this is helpful.

S.

Warm it up, reset the MPG-ometer, drive at 60mph on the motorway and see what economy it gets. Should easily be over 50, probably 60mpg.

That way you know if its a problem with a car, or just the nature of the journeys you are doing.

ssmith1979
I have the 175BHP version of your engine in my Megane.
Don’t panic – it is about right!
I now consistently get 38MPG from a mix of town and motorway driving.
What I found with mine was that it didn’t really loosen up and start producing decent figures until about 35k miles. There was an improvement of about 20% at this point…
Hope this is helpful.
S.

Thats very helpful, thanks.

I understand the principles of driving to achieve good economy and am using many at the moment. Im just used to seeing higher figures quoted (with seeminlgy less effort to produce them) on OBC’s (admittedly mainly VAG cars) of 50’s & 60’s, seeing an average in the 30’s on my car was what left me worried.

I’ll being going for an Italian style tune on the way home and will keep a close eye on actual figures (havent owned it long enough yet to be sure), I ran some figures earlier and if I get the range the my computer is telling me then I should be getting somewhere between 43 and 45mpg for this current tank.

If it doenst loosen up a bit over time i’ll look to have the EGR valve etc cleaned/checked.

If 45mpg is realistic then I can probably live with it, but given the rising price of diesel over petrol it really seems more likely that I should have spent less on a petrol engine.. 🙁 (or plumped for a 2.0 VAG diesel)

I get 40 mpg in my 2l Renault Turbo Diesel. It is in a Trafic van though……..

My VAG diesel is supposed to have a new air filter at 30,000 – but changing it at 10k or 15k makes a big difference to low RPM pull and the economy. Service it, then boot it for a good run (when it’s warmed up of course) – that’d be my first call.

I drive a Volvo V50 deisel at work as a response car…..with “spirited” driving I can get the dash readout to show the fuel economy as 9mpg….

As far as things clogging up go – the DPF is a good candidate. Even when working properly they will restrict exhaust flow a bit. The car will be set to regenerate it when it gets to say 50% clogged, but it won’t go back to zero and if you are doing town driving it’ll spend a lot of its time at 20 or 30% clogged I guess.. Not only that but the regeneration itself uses fuel.

If your car spends its time on the motorway thne not only will it not generate much smoke but the exhaust temperature will be enough to clear it out anyway.

Trouble with modern oil burners is they have got them to close to the performance of a petrol and up the HP and the power band and this has decreased the economy, 25 years ago when they were slow off the mark, no turbos and diesel was way cheaper than petrol this is when I was first driving diesels, you would get way better economy, you have to look hard and do plenty of research to find a good frugal diesel these days, Passat are good, friend of mine before his company gave him one of them daft electric/petrol cars was getting 60plus (loads of motorway miles), Im run a Focus TDCI 1.6 Estate and am very please with its economy, ave 49mpg and low down torq. used every day as a work horse.

Fiat Doblo 1.3 turbo, 85 hp.

Mixture of very steep, slow speed stuff and motorways – 45 mpg average.
I’m quite happy with that.

Average speed is only 22mph!

his company gave him one of them daft electric/petrol cars was getting 60plus

I’ve got a daft petrol electric car, it’s more economical than my Passat. 60mpg motorway and never less than 50 even in stop start town. You can keep your 35mpg diesels in traffic.

I also used to have one of these old simple diesels you talk about. 45mpg was about the best I could do. And it only had 75hbhp, compared to my silly electric petrol car with 105bhp.