Reply to: Mpg

[Zorba]

Focus Diesel has to be the best commuting car out there.

Cheap to buy, cheap to run and doesn't attract any attention whatsoever.

It's top of my list to replace my Passat. Mrs Z has one and often gets 50+mpg out of short runs!

[rootsnall]

As said by others diesel is more energy dense than Petrol. Also the way a diesel works is different to petrol.

Diesel burns where as petrol explodes. Diesel heats the air in the cylinder as its burns causing it to expand where as petrol explodes using the air up in the explosion but also causing the resulting gases to expand.

On a car becuase the fuel air mixture remains pretty constant in that at low power the car uses a throttle to stop as much air coming into the engine i.e. half power you are not getting a full 2l of air into your 2l engine each rotation.

You may get 1l of air in and use half as much petrol.

In a diesel there is no such distinction. The engine takes a full gulp of air each rotation and the amount of fuel entered is varied. I.e. at full power lots of diesel and at low power not as much.

Means a more efficient process.

Right !

It's all academic now as I'm stuck with my petrol Mondeo for the next decade or so.

[IR35 Avoider]

That's what i thought. So what's up with these stats showing that the best petrol engines are getting better mpg than diesel?

They don't. The very best petrol (disqualifying hybrids) is Peugot 107 at 61.3, the best diesel 68.9. If you run your eye down the list, nearly all the diesels are about 65mpg, but the bottom half of the petrols figures start with a 5.

Yes, one of the three petrol hybrids is better than any diesel, but that doesn't prove anything about petrol versus diesel, just that hybrid technology delivers something in return for the thousands extra it costs to put in a car. In fact a lot of people in the car industry think hybrids are a carp concept and that straight diesels can beat them for economy. Having said that, I think some are going to come around, Citroen have shown a concept version of a diesel hybrid version of the C4 with (I think) the electric wheel motors I'm so keen on.

[Sockpuppet]

Why does diesel get so much more to the gallon ? Better engine or better fuel. I toyed with getting a diesel Mondeo last week but plumped for what I knew, the 1 year old diesels were a grand or two more but with that margin of difference in MPG it would pay for itself in no time.

As said by others diesel is more energy dense than Petrol. Also the way a diesel works is different to petrol.

Diesel burns where as petrol explodes. Diesel heats the air in the cylinder as its burns causing it to expand where as petrol explodes using the air up in the explosion but also causing the resulting gases to expand.

On a car becuase the fuel air mixture remains pretty constant in that at low power the car uses a throttle to stop as much air coming into the engine i.e. half power you are not getting a full 2l of air into your 2l engine each rotation.

You may get 1l of air in and use half as much petrol.

In a diesel there is no such distinction. The engine takes a full gulp of air each rotation and the amount of fuel entered is varied. I.e. at full power lots of diesel and at low power not as much.

Means a more efficient process.

[DimPrawn]

That's what i thought. So what's up with these stats showing that the best petrol engines are getting better mpg than diesel?

small light city cars are better with a small modern petrol.

As the car gets bigger and heavier (think tank like 4x4) a modern diesel makes more sense.

In town driving a diesel is not much better than a tiny 1000cc petrol.

[TimberWolf]

Diesel as a fuel is more energy dense than petrol and the engine is more efficient too.

That's what i thought. So what's up with these stats showing that the best petrol engines are getting better mpg than diesel?

[DimPrawn]

Chav car

If you say so bag-o-pus.

I would have said Chavs drive souped up Corsas, Nissan 200/300ZX, and other vehicles that have more bolt on spoilers.

Never seen a chav in a Focus Diesel, just ordinary working people.

[Ardesco]

LPG is what I was seriously looking at. You can get about 300 miles out of a tank the size of your spare wheel, it is higher octane than petrol and costs half the price (Although expect the government to double the price if lots of people move over to it)

It costs about *1500 to *2000 to get it installed though and considering my current car has done 140k I decided not worth it. I'm going to wait until I get a new car (Next year assuming all goes well).

As for the MPG I get an average of 30MPG from my petrol A4. From talking to people I know Mundaneo's do the best MPG.

[Bagpuss]

Focus Diesel has to be the best commuting car out there.

Cheap to buy, cheap to run and doesn't attract any attention whatsoever.

Chav car

[Troll]

Diesel as a fuel is more energy dense than petrol and the engine is more efficient too.

yeah... what I said

[VectraMan]

As an aside - I thought all new cars were going to go to 24volts so things like power steering & air con pumps could be run electric rather than off the engine drive thus reducing consumption further.

Not heard anything about it recently

Would running off electricity be more efficient? You'd need a bigger alternator to power it which would cancel out some of the benefit. And whereas aircon has a clutch so can disconnect when not in use, the alternator would always be driven.

S2000 has electric power steering. And I think MR2s have electrically powered hydraulic pumps for power steering.

[chef]

Of course, you could go by train from Manchester to Reading....

I'm sure it only costs about £100/day on the train.

it's £106 each way on the train.. which i have done.

the only problem with that is I dont like staying in the city centre lifeless hotels and much prefer to be somewhere with a bit of character and a decent menu which are usually out of town. That then means i'd have to get a taxi to/from work each day which is more costly than driving mon & fri.

plus i really enjoy driving

[DimPrawn]

more efficient
HTH

Diesel as a fuel is more energy dense than petrol and the engine is more efficient too.

If you are covering huge distances on motorways then a modern Diesel makes sense. If you do like 8K miles pa. mostly in town, a small efficient petrol engine is best.

[BoredBloke]

I get about 44mpg out of my Mondeo TDCi, but I don't tend to drive it at its most fuel efficient speed!

I'm only doing Rochdale to Leeds each day, about 40 miles and a tank does me for the whole week and a day. But that also covers me for the fact that the thing is in perpetual motion over the weekends. My last Mondeo had the old 90bhp engine. I could leave home on a Monday morning and get to Uxbridge (220 miles later) through rush hour traffic, do all my driving around down there and get back on the same tank at the end of the week. Again - never driven at the optimum speed for the best mpg.

Now cue Milan for tales of frugal diesel usage in his Passat. How it can get to the moon and back on a teaspoon of diesel.

[VectraMan]

Of course, you could go by train from Manchester to Reading....

What's the mpg of a train?

34mpg from my Primera, which is mostly on the motorway. That's according to the trip computer, which this morning told me I had only 8 miles before running out of fuel, so I filled up and only got 2/3rds of a tank in. Stupid thing.

Oh and it has a cam chain (as does my S2000).