Afternoon All,

Think I have settled on a new (used) car. The only thing in the back of my mind is that the combined fuel (diesel) economy is about 46mpg 😕

The car I will be replacing (again a diesel) by my reckoning gets about 55mpg on a long run (motorway).

In reality am I going to find the difference greatly costing us?

Also…

How believable are manufacturers MPG published figures?

Neither myself or Mrs LMTTM are particularly heavy footed but I guess we are unlikely to get much more than the quoted combined figure? Are we….

autotrader tech data will give you the combined and the city/highway values (combined is just an average of the two IIRC). Your current car will get 55 on the motorway, yo'll probably find a car with 46 combined will get about the same as your old car on the motorway too. Combined is a fairly good representation of a 10 mile commute down some country roads into the centre of a city, for me at least.

Good to know CK.

**off to check auto trader**

How believable are manufacturers MPG published figures?

Generally, not even close

PeterPoddy – Member

How believable are manufacturers MPG published figures?

Generally, not even close

+1. Take at least 10-15% off manufacturers combined figures, more off the urban.

What car is is, by the way?

There may be someone with some experience of it 🙂

I have found that the 'combined' figure is about what you'll get on a long motorway run, which as I understand it should be the 'extra urban' figure.
The extra urban always seems hopelessly optimistic.

Do you do loads of miles?

Assuming 12k miles/yr, 55mpg & 46mpg averaged over those miles respectively & £1.20/ltr diesel:
55mpg will cost you £1188/annum
46mpg will cost you £1421/annum

a difference of £233/annum or £19.50/month. Of course if you do twice the mileage, it'll be twice as much.

Here's the figures for mine:
Fuel consumption (urban) 40.9 mpg
Fuel consumption (extra urban) 65.7 mpg
Fuel consumption (combined) 54.3 mpg

Town-only short hops I tend to get 42-44mpg, combined I get 52-54, motorway at low cruise I've seen 67 but generally sits around 60 if driven at 55-60mph. At 70/not thinking about it, it jumps down to 55-56mpg. Bear in mind that the urban is averaged at something like 20mph and the extra urban is meant to be measured at 40 (i.e. in 5th at 40mph, virtually idling).

http://www.telegraph.co.uk/motoring/caradvice/honestjohn/6936339/Honest-John-Average-fuel-consumption-figures-differ-from-manufacturer-claims.html

http://www.telegraph.co.uk/motoring/caradvice/honestjohn/6936344/Honest-John-Why-petrol-engines-are-better-for-lower-annual-mileages-than-diesel-engines.html

Peter…

Toyota Auris SR180 – I guess performance **cough** is the trade off on this one…

Stumpy…

We would do about 18k a year 😕 Thank you for the maths – not my strong point – doesn't seem too scary a difference…

Macavity – Member

http://www.telegraph.co.uk/motoring/caradvice/honestjohn/6936339/Honest-John-Average-fuel-consumption-figures-differ-from-manufacturer-claims.html

http://www.telegraph.co.uk/motoring/caradvice/honestjohn/6936344/Honest-John-Why-petrol-engines-are-better-for-lower-annual-mileages-than-diesel-engines.html

Cheers for the links – interesting stuff.

Modern diesels have: EGR valves, Diesel Particulate Filters, Dual Mass Flywheels, Inlet manifold swirl flaps, Turbochargers and Intercoolers, High pressure Injection Pumps, Highly sensitive Injectors, Many have timing belts.

Modern petrols (and indeed ones for the past 10 years!) have EGR valves, dual mass flywheels, inlet flaps, turbochargers, intercoolers, multiple injection pumps and highly sensitive injectors, CATs. Oh, and timing belts. Silly argument. Essentially all that has happened is D technology has caught up with petrol.

My recent experience ( over the last 12 months ) is that I have achieved about 25% better mpg by driving more smoothly, not accelerating fast, predicting traffic flow to avoid braking and travelling a bit slower.

This is on a petrol car, but I cannot see why the same should not apply to a diesel.

Smooth / slower driving approx 400 miles per tank.
Previously approx 320 miles per tank.

You may find this makes the difference between th enew and older car.

I find I am quite a smooth driver as this is necessary to get even a modicum of performance out of my current car (very small band of actual grunt).

We get nearly 600 miles off of a full tank of fuel so hearing 400 (I know the case above is petrol) leaves me worried.

Hmm.

What car/engine Coffeeking?

Does depend how big the fuel tank is of course.

Done pretty much the same change.

The new car has a slightly bigger fuel tank, so the range is about the same, so I'm not having to refill any more often. The bill is obviously higher for a full tank, but no, it's not massively affecting me.

As for official figures. Well the old car (a VW) was spot on, based on brim-to-brim calcs, and the OBC agreed too. The new one – manufacturers figures are about 7mpg higher for combined (they reckon 52), whilst the OBC reads about 7mpg under (37) which horrified me a tfirst until I started working it out on paper and came up with 45 based on brim to brim.

What car/engine Coffeeking?

306 HDi estate (2.0 90hp).

does anyone know of a aftermarket computer for cars (or more probably boats?) that shows fuel flow? Quite fancy knowing what the midget actualy does MPG wise. I know it does >320miles on a tank which costs about £30 to fill, but that gives 55mpg on the back of an envelope, which cant be right for a carb fed 'sports' car!

Our Tr6 is lucky to get 25mpg!

IIRC there was a test on fifth gear that actually found the manufacturers claims weren't far off the mark, so I guess it depends who you believe!

Here it is: http://www.youtube.com/watch?v=AVOi1HSROZo

I also have a diesel (astra) but was thinking next time to go for a petrol and get it converted to LPG to save cash on fuel (I do about 500 miles to work and back a week) I'm not sure if LPG petrol stations are all over the place or just around here……

Modern petrols (and indeed ones for the past 10 years!) have EGR valves, dual mass flywheels, inlet flaps, turbochargers, intercoolers, multiple injection pumps and highly sensitive injectors, CATs.

Yes, but petrol engines are far less likely to lunch EGR valves and DMFs as a rule – they don't run sooty, and they don't have anywhere near the violent torque spikes a diesel does.

The only thing on that list a you'd expect a petrol to munch is the turbo, as petrol ones run rather hotter. However, the only "normal" car I know of with a reputation for doing turbos in is the 320d, as they're thrashing a small turbo hard to get big power out of the diesel engine without a lot of log.

My diesel Astra (1.9CDTi 150)was meant to be near 50 – I got around 40
My BMW (335d) is meant to be around 40ish – I average 31mpg.

thisisnotaspoon in talking about fuel consumption SHOCKER 😉

letmetalktomark – so if you do 18k miles/yr, multiply my values by 1.5 & you're there.
So that's £349.50/yr or £29/month…..

There's a German website somewhere (can't remember the url) that people submit their measured fuel consumption.

There's data on it for most cars and hundreds of users for most, so you can get a pretty good idea of the average real world economy of most cars from it (at the cars I've looked at typically 10-15% less than the manufacturers combined figure).

EDIT: here it is: http://www.spritmonitor.de/en/

My Golf is supposed to get around 55MPG it gets 58mpg average and I can get 65+ with ease and still drive sharpish. Record yet is 91mpg on a 18 mile run very steady with cruise on.

Drive like a bit of loon I still get 55 with ease.

Measured by the trip computer Drac?

haha, I need to do a run to Oxford on the A-roads tomorrow, I'll brim the tank and let you know the results. I reckon it makes a massive difference in the midget whether your on the motorway or not, because I know its crap economy on b-roads and arround town but it does seemt o go a very long way on the motorway between fillups.

Measured by the trip computer Drac?

Yup but it is pretty accurate as done rough calculations too.

So a claimed combined 46mpg is really quite poor then for a medium sized hatchback 🙁

Drac – what Golf is that?! Must be a Bluemotion thingummy?

Did some nerdy tests in mine the other day – at least 10 seconds on a flat level motorway:

65mph – off the scale (about 55mpg)
75mph – just under 50mpg
85 – just over 40
95 – just over 30

Shows how much more that extra speed uses but the real killer is (my car has both an mpg analogue gauge and a digital one) is any acceleration – do anything but the lightest of throttle openings and it slams straight into the top end (worst mpg) of the scale – under 16mpg!!

I know accelerate by sticking my feet out of the door and pushing.

Drac – what Golf is that?! Must be a Bluemotion thingummy?

God no, it's the MkVI TDi no Bluemotion may brag high miles but it seems you have to drive like a Grannie or it suffers for it.

Yes, but petrol engines are far less likely to lunch EGR valves and DMFs as a rule – they don't run sooty, and they don't have anywhere near the violent torque spikes a diesel does.

Got 3 D's in the family, all 3 with EGRs, total of over 150K miles on them all, all bought around the 100K mark – no EGR lunching going on here. DPFs are fine. Dunno what you're on about!

Is that the same engine that goes in the Verso T180? If so there is a thread on the Toyotaownersclub forum with a lot of people moaning that they get nowhere near the stated mpg.

My 2.2D4D Verso(140bhp)is pretty close to the manufacturer's claims, around 43mpg combined.

coffeeking – Member

What car/engine Coffeeking?

306 HDi estate (2.0 90hp).

Can I point and laugh 😀

God no, it's the MkVI TDi no Bluemotion may brag high miles but it seems you have to drive like a Grannie or it suffers for it.

2.0 litre or 1.6 diesel? Sorry to go on but that really is very impressive mpg!

My old Astra 1.9CDTi (150) ate swirl flaps at 42k miles – under warranty but had it not been, it would have been a killer. Apart from that (!) it was a very decent car.

35d unit seems pretty reliable according to people "in the know."

Flipping hope so…!

2ltr version it's crazy I know a brilliant car I had a few mkV before that and they were great but got no where near the same.

Now that is impressive – even the lower powered version is a nippy machine.

My wife's Audi has the same engine as Drac's and she sees low fifties for the most part (although she does drive like an old granny)