MPG claims + petrol v. diesel

[Deleted member 48021]

I have been reading various MPG claims in the forum and can't compete! I have a Talbot Harmony petrol and only achieve low 20's - even driving carefully. Similar models with diesel I hear achieve over 30MPG. And yes, my tyres are pumped up, not all my driving is uphill, and I don't have the pedal to the floor (although she doesn't exactly perform like a Formula one!)

 

[RichardHelen262]

I have a sprinter diesel and only achieve low to mid 20's I don't know how these people with coach builds get mid 30's but if it is only used for holidays does it really matter ?
You will have made the saving when you bought it as had it been a diesel the chances are it would have been more money to buy

 

[Tbear]

I have been reading various MPG claims in the forum and can't compete! I have a Talbot Harmony petrol and only achieve low 20's - even driving carefully. Similar models with diesel I hear achieve over 30MPG. And yes, my tyres are pumped up, not all my driving is uphill, and I don't have the pedal to the floor (although she doesn't exactly perform like a Formula one!)

I have a Peugeot Boxer with a 2 litre petrol engine. I find it better not to work out my MPG unless I am on a long run with the wind behind me. It's a fully loaded van. What do you expect? A good service may help and a compression test may give a clue to why so low but I suspect removing weight is the only way to improve it. Failing that, ignore fishermans stories when it comes to mileage.

Richard

 

[antiquesam]

I used to have an app on my phone to give mpg on the van, which is a '95 Ford Transit chassis with a coachbuilt body and it stuck relentlessly at 23-24 mpg. When diesel was 135p a litre this was too depressing to look at, but isn't quite so bad at £1 a litre.

 

[phillybarbour]

Low 20s on that era of petrol van would seem reasonable to me. Newer vehicles will do better but then depreciation is higher. If your vans tidy your on to a good thing overall so try just to enjoy it as that mpg is to be expected.

 

[Deleted member 9849]

I have a 2.8 diesel and the fuel economy is usually around 25 give or take 10% either way depending on driving conditions and terrain.I worry more about servicing and sourcing spares as it's very easy to pay over the odds for these.I try not to get too worried about mpg,I didn't get a motorhome for economy reasons,it's the lifestyle I bought into.

 

[Siimplyloco]

We averaged 24 mpg this season fully loaded and traversing all sorts of terrain. Quite happy! When tugging with a 2004 Kia Sorrento we only got 21!
John

 

[Teutone]

I have a sprinter diesel and only achieve low to mid 20's I don't know how these people with coach builds get mid 30's but if it is only used for holidays does it really matter ?
You will have made the saving when you bought it as had it been a diesel the chances are it would have been more money to buy

I can tell you how. They only drive with 50mph on the motorway.

I tried it on a trip where we had plenty of time to get to our destination. You can save by driving slow. But boy it is SLOW! I can't do this. On average we do 60mph and I am happy to pay the difference for the more consumption. We are not too bad, ours is a low profile with no overcab bed. I still manage 30mpg ish.
I found that weight isn't too much of a mpg killer, it's the aerodynamic. If you have a overcab bed your mpg will go up a lot for every 5mph you drive faster.

 

[listerdiesel]

Gearing affects it as well, plus engine size etc etc., but as already said, the cost difference on fuel over a trip isn't really worth worrying about.

Towing our big trailer with the show engine loaded drops us down to 10-12mpg on hilly country, but the Discovery runs on LPG so costs aren't too bad.

The Mercedes is geared for 50mph running and will do 20-25mpg, but it is a 6-tonne van and has a 4.25 litre turbo diesel engine, built for comfort, not for speed

Peter

 

[ricc]

to get the mpg a diesel is capable off you need to understand the differences between the characturistics of petrol and diesel engines.
petrol engines have little torque (twisting power or grunt) at low revs so need to be reved to pull the skin off a rice pudding .
a good diesel produces near enough the same torque throughout the rev range , torque at 1000 rpm is near enough the same as at 4000 rpm .
what this means in practice is that at a given road speed you can be in a higher gear in a diesel.... the less revs the engine is doing the less fuel its burning.
in practice you can be changing up a gear at 2 to 2.5k rpm and not changing down till arround 1k rpm.

as a student many years ago we had a david brown engine on a dynamometer doing hp,torque and fuel consumption measurements at varying loads and engine speeds. most of us got a bollocking for not being brutal enough on the high load/ low speed part of the test.... ie not loading the the engine to phutt phutt stall point at arround 500 rpm.


another factor , probably not really relevent to motor homes is on short journeys a petrol engine gives abismal mpg untill its warmed up whereas a diesel mpg is pretty good even on a cold engine.

in short if you drive a diesel like a petrol , using high revs you wont get the high mpg figures.


dont forget fuel consumption is only one aspect of lifetime cost. servicing costs and engine life span also have to be taken into account.

ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel. you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.

 

[Teutone]

ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel. you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.

these days I am more inclined to look at a petrol engine for longevity and low service cost than a diesel. Most modern diesel engines are around 2 liter capacity and turbocharged pumping out 150-180bhp! Fair enough, the economy and grunt are outstanding but to achieve this they are full of computers, sensors, recirculating system, coolers, filter and and and. Everything is stretched to the limit and if things go wrong you are either faced with a huge bill as a result of extensive fault finding (from replacing every sensor, filter etc from front to back) or a huge bill from the engine going pop and it's not economical to repair it because all the tech around it needs to be replaced same time.

So if your "old" diesel is a little bit more thirsty than all these new high tech diesels, it may well not be more expensive in the long run.

PS something about tourque. There is no replacment for displacement :wacko: (or a turbo charger.....)

 

[Siimplyloco]

SNIP

ive no experience of modern (under 15 year old engines) but historically youd expect a diesel to outlast 2 perol engines and the servicing costs to be lower on the diesel. you didnt have ignition componants ,(spark plugs , leads distributor caps , consencers ) to routienly replace or adjust or fail on a wet night.

Good info here, but those simple bits have been replaced by much more complicated bits!
John

 

[Deleted member 9849]

I can tell you how. They only drive with 50mph on the motorway.

I tried it on a trip where we had plenty of time to get to our destination. You can save by driving slow. But boy it is SLOW! I can't do this. On average we do 60mph and I am happy to pay the difference for the more consumption. We are not too bad, ours is a low profile with no overcab bed. I still manage 30mpg ish.
I found that weight isn't too much of a mpg killer, it's the aerodynamic. If you have a overcab bed your mpg will go up a lot for every 5mph you drive faster.

50mph on a motorway is too slow and I would suggest hazardous.The HGV's would be constantly pulling out into lane 2 to get past,then cars travelling in lane 2 pull into lane 3,then all the Audis,Beemers and Mercs that are in lane 3 have to brake sharply.

 

[Teutone]

50mph on a motorway is too slow and I would suggest hazardous.The HGV's would be constantly pulling out into lane 2 to get past,then cars travelling in lane 2 pull into lane 3,then all the Audis,Beemers and Mercs that are in lane 3 have to brake sharply.

don't know when the last time was you drove on the motorway. I can see what you described on a daily basis. There are CARS driving slower than HGV's and as a result HGV's are constantly pulling out into the second lane just to be overtaking by another HGV in the thrid lane.

I feel for the time pressure the HGV's have these days but recently there seemed to be NO RULES for HGV's anymore. Just drive into a temp speed limit zone on the motorway. You will be surrounded by HGV's left righ and centre ignoring the 50mph limit sitting behind your bumper with a 10inch gap. Some even flash you to get out of the way.

And yes, 50mph is too slow on the motorway.:wave:

 

[izwozral]

My first MH was a Talbot Express, petrol and LPG, on petrol I reckon it did 22-24mpg on a long straight run, on lpg my guess is 26-28mpg. it certainly ran smoother with better oomph on lpg and was bit of a cart horse on hills using petrol.
I sorta miss that old bird, whether it was because it was my first or I had grown to love it's little foibles, I don't know.
There was a Talbot Express on Ebay a couple of years ago with verified 1200 odd miles on the clock, it was in A1 condition inside and out, if my memory serves me right, it sold for around the £12k mark. I still get a twinge of regret not going for it.

 

[Roger Haworth]

I presume everyone here is measuring m.p.g. by filling the tank, driving how ever many miles, then filling the tank again and dividing the miles driven by the gallons used between fills.

If on the other hand any of you are using the vehicle's computer to measure m.p.g. you are in my experience likely to get a very significantly different figure. For example on my van (Fiat Ducato 100 Mulitijet engine) if the computer says it's doing 36 m.p.g. the real figure, calculated as above, works out at about 30 m.p.g. My car is not quite so inaccurate - if the computer says 50 m.p.g. the real consumption figure is about 47 m.p.g.

The other variable is the vehicle's milometer - how accurate is this? I suspect that most of these record more miles than you have really covered!?

1 gallon = 4.54 litres.

 

[Teutone]

I presume everyone here is measuring m.p.g. by filling the tank, driving how ever many miles, then filling the tank again and dividing the miles driven by the gallons used between fills.

If on the other hand any of you are using the vehicle's computer to measure m.p.g. you are in my experience likely to get a very significantly different figure. For example on my van (Fiat Ducato 100 Mulitijet engine) if the computer says it's doing 36 m.p.g. the real figure, calculated as above, works out at about 30 m.p.g. My car is not quite so inaccurate - if the computer says 50 m.p.g. the real consumption figure is about 47 m.p.g.

The other variable is the vehicle's milometer - how accurate is this? I suspect that most of these record more miles than you have really covered!?

1 gallon = 4.54 litres.

agree you can't rely on the dash. I measure tank for tank andmy speedo is quite close to the GPS. You have to use the speedo, there is nothing else?
But the safe method is always to fill up to really full (till you can see the level) and fill up again. Bit inconvenient but you don't need to do it all the time.
I have recorded miles and all diesel along the trip and as long as you fill up to full at the end even part filling can be taken into the calculation.
So my dash thingie isn't far out. 2-3mpg

 

[Tezza33]

On our last trip to France in August I measured from a full tank at the beginning to a full tank at the end, it worked out using the mileometer at 35mpg, but my speedo is wildly inaccurate, at 80kmh my satnav shows me doing 40mph instead of 50mph and that is confirmed when a roadside display tells you your speed, every trip I keep meaning to check the accuracy of the mileometer as well but I forget until I get home, 20% out is a lot though and brings my mpg figure down to 28mpg which I think would be about right, Hymer 584, 2.8jtd which is rarely out of 5th gear and my figures are always better in France, I don't see the point in worrying about it anyway, it is still cheap

 

[Penny13]

My Fiat Ducato low profile gets 25 to 26 per gallon, it's now in its third year from new ! I don't do technical it's what the computer tells me. I drive about 55 to 60 with lots of road variations.

 

[jagmanx]

27 Plus Honestly !

Nearly 30 MPG sometimes
2.5 Litre Diesel on a Renault master.
As others have said ..Keep below 55 MPH
Look ahead
I have recently fitted a
...
Standard Tunit

3 Year Warranty
1 Year Engine and Drive Line Warranty
Typical fuel saving of 12%
R.R.P: £375.00

This has made an improvement so now usually ALMOST 30 MP always

Obviously mountains etc have an impact but " A LIGHT RIGHT FOOT" is the key just ease off and your MPH will not drop !