Petrol vs Diesel - interesting...

I have just been researching this for one of my clients and discovered something very interesting...

If you compare a BMW 530SE with a 535d SE (both have almost identical 0-100 kph times of 6.5 and 6.4 seconds respectively), the diesel is just under 12% more economical than the petrol. However, by coincidence, it costs almost exactly 12% more :shock:

When you consider that diesel costs about 4% more in the UK, that results in a fuel cost difference of around 8%.

At todays prices the difference in fuel cost is just over 1p per mile, yet the price difference is £4800. So you would have to do well over 400,000 miles before you saved a penny on fuel costs!

So, remind me again, why we have become obsessed with diesels in the UK?

Point very well made Wattie. I think it's more to do with the perception that one is getting more value for money out of a diesel than a petrol. This self-fullfilling prophecy is reflected come re-sale time and you'd notice how much stronger residual values are for diesels than they are for petrol cars.

If I was buying privately and brand-new then I would certainly ponder this case and I think I would go for petrol. On the second hand market (which is where I have always done my shopping for cars) are the percentages as marked as the ones you have quoted?

~ Maxie :?:

Just to add to that, I've also discovered that the BIK % on the diesel is 25% against 22% on the petrol - so you'll not only pay a higher % of tax, but on a higher amount too!

The trouble is, when people compare petrol with diesel, they never compare like with like: Of course a 150 bhp 4-pot diesel is going to be more economical and have lower emissions than a V6 240 bhp petrol :roll: , but it ain't going to beat the petrol car away from the lights... :wack:


I feel my anti-diesel campaign growing by the minute... :hand:

To add, one of the big problems facing the industry is the quest for reduced CO2 levels has meant the cost of diesel tech has increased significantly in the last few years and still will continue, thus causing this price difference to further increase

the irony is that although diesels retain more value after x years, they still cost more to buy and run in the 1st place, so do they really save money ?

Maxie Islam said:

Point very well made Wattie. I think it's more to do with the perception that one is getting more value for money out of a diesel than a petrol. This self-fullfilling prophecy is reflected come re-sale time and you'd notice how much stronger residual values are for diesels than they are for petrol cars.

If I was buying privately and brand-new then I would certainly ponder this case and I think I would go for petrol. On the second hand market (which is where I have always done my shopping for cars) are the percentages as marked as the ones you have quoted?

~ Maxie :?:

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Percentage difference in used values is even higher generally - take for example used Discovery: There's a 9,500 mile Petrol HSE that can be had for £20,000 at the moment, whereas the TDV6 (with less than 2/3 of the power and taking half as long again to reach 60mph) will typically set you back anywhere between £22k and £28k - and it was £2000 less to buy in the first place.

It just seems that logic and common sense just don't enter the equation :?

Not even the cancer and asthma sufferers will argue against the cars that probably caused their problem in the first place! They all want to do their bit for the planet and save a bit of CO2 (or so they believe) :floor:

Can't argue with the figures you have quoted but in the many years I've been doing the calculation, I've NEVER found a comparable petrol/diesel model where the petrol has been cheaper in tax terms. Millions of others have come the to the same conclusion because they have swapped to diesel company cars.

Perhaps your campaign should be redirected to ask why, having changed to an emmisions based tax environment that clearly favoured diesels, the LABOUR goverment then increased duty disproportionately on diesel and also added 3% to BIK figures?

As far as I can tell, none of the additional revenue has been invested in public transport, road improvements, or particulant emmission prevention (which can all be resolved by legislation and engineering anyway).

Personally I think you are barking up the wrong tree trying to say petrol engines are in some way better than diesel. There are many applications where this is demonstrably not the case.

However, there are also in this ever developing world, cases where the advantages of one or other are being reduced. I suspect we are getting closer to the point where people will opt out of the company car system.

This of course will not help emissions as they will all go out an buy second hand petrol guzzlers like V8 Landies and 996 Carrera's

Tiptop Topcat said:

Can't argue with the figures you have quoted but in the many years I've been doing the calculation, I've NEVER found a comparable petrol/diesel model where the petrol has been cheaper in tax terms. Millions of others have come the to the same conclusion because they have swapped to diesel company cars.

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You have now! Unless you mean comparable in terms of PURCHASE PRICE alone? In which case they absolutely will not be comparable in terms of performance, and confirms that diesel engines are massively more expensive than their petrol equivalents.

Perhaps your campaign should be redirected to ask why, having changed to an emmisions based tax environment that clearly favoured diesels, the LABOUR goverment then increased duty disproportionately on diesel and also added 3% to BIK figures?

As far as I can tell, none of the additional revenue has been invested in public transport, road improvements, or particulant emmission prevention (which can all be resolved by legislation and engineering anyway).

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The higher BIK for diesels reflects the additional local health hazard hence all diesels without a DPR filter are banned from Stuttgart city centre.

Personally I think you are barking up the wrong tree trying to say petrol engines are in some way better than diesel. There are many applications where this is demonstrably not the case.

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I agree: Genuine off-road use and trucks! :wink:

However, there are also in this ever developing world, cases where the advantages of one or other are being reduced. I suspect we are getting closer to the point where people will opt out of the company car system.

This of course will not help emissions as they will all go out an buy second hand petrol guzzlers like V8 Landies and 996 Carrera's

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Guess what I did 15 years ago? Haven't had a car with less than 200 bhp since and only one was a 'never to be repeated' noisy, smelly, horrible oil-burner!

Will this see a rise in the so called eco-petrol cars, which the VW Group have PR'ed with the FSI engine range which were far more economical and eco-friendly than the old, but which all carry a 'cost'... but cars getting heavier due to safety legislation more power is needed ?

Sorry Wattie but cannot agree with the assessment of performance. I found that when looking at power and torque, one normally had to go up the range to achieve comparable characteristics.

I don't have the brochures to hand but I'd guess we're talking comparing a 320d with a 325i rather than the 318i and 320i. 320d was then not only cheaper but the BIK would be a good 5-7% less.

I have also found that the combination of torgue with auto gearboxes or the lower gearing of manuals made the diesel engined cars far better for everyday driving.

This changes with more powerful cars but that doesn't have much to do with the the reasoning behind this particular debate.

However, what does seem to be changing is the type of vehicle. I've been quite impressed by the improvement in quality of more mainstream cars and the engineering beneath their skins. With congestion and running costs on the increase, there are quite a few "small" cars that make a good case for themselves, as the cheaper purchase and fuel costs associated with the petrol variants balance the BIK calculations.

That is of course until LABOUR recoginse the trend and put duty up on Petrol!

We are going to have to agree to disagree on this one I'm afraid... As I said in the original post it was a direct comparison between a BMW 530 SE petrol and a BMW 535d SE diesel. The figures are 6.5 and 6.4 secs 0-100 kph, 37.7 mpg and 42.2 mpg, both have CO2 emissions of 178 g/km (with auto box) the 530 is £34,620 and the 535d is £39,420

The closest priced version to the 530 petrol is the 530d and stats are: 6.8 secs (so a tiny bit slower), 42.8 mpg, 176g/km, and £34,970... So more expensive, more BIK, slightly slower, but this time you would only need to do 35,000 miles to get your money back on the fuel cost (but you'll still not get your extra tax back until you've covered an additional 40,000 miles per year)!

This whole diesel obsession is ridiculous - both petrol and diesel will run out at the same time eventually, so why skew the industry into investing billions into small diesel engine development, when a similar amount spent on developing new sustainable technologies would be much better in the long term.

The politicians single-minded focus on CO2 alone has caused this, and the jury's still out on the whole subject of human influenced climate change anyway! Whereas it is a well proven fact that NOx causes and aggravates asthma (especially in children) and that Particulate Matter is carcinogenic.

Sorry to rant, but I absolutely loathe the smelly, dirty, toxic emissions from diesel engined vehicles: When was the last time you switched the recirculating air button behind a petrol engined car? (Unless it was burning oil just before it broke down).

Wattie said:

We are going to have to agree to disagree on this one I'm afraid... As I said in the original post it was a direct comparison between a BMW 530 SE petrol and a BMW 535d SE diesel. The figures are 6.5 and 6.4 secs 0-100 kph, 37.7 mpg and 42.2 mpg, both have CO2 emissions of 178 g/km (with auto box) the 530 is £34,620 and the 535d is £39,420

The closest priced version to the 530 petrol is the 530d and stats are: 6.8 secs (so a tiny bit slower), 42.8 mpg, 176g/km, and £34,970... So more expensive, more BIK,

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Well that's interesting and a surprise; if you'd told me in the pub I wouldn't have believed it. 530 petrol injection = twin turbo diesel :?

slightly slower, but this time you would only need to do 35,000 miles to get your money back on the fuel cost (but you'll still not get your extra tax back until you've covered an additional 40,000 miles per year)!

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The stupidity of the current UK BIK tax system is that it focuses on capital cost and emissions. Obviously none of our cars are used for private use so the fuel benefit does not come into it.

This whole diesel obsession is ridiculous - both petrol and diesel will run out at the same time eventually, so why skew the industry into investing billions into small diesel engine development, when a similar amount spent on developing new sustainable technologies would be much better in the long term.

The politicians single-minded focus on CO2 alone has caused this, and the jury's still out on the whole subject of human influenced climate change anyway! Whereas it is a well proven fact that NOx causes and aggravates asthma (especially in children) and that Particulate Matter is carcinogenic.

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From a laymans point of view, it does seem that the economy differences and hence emission outputs for petrol and diesel engines are converging, driven I suspect by the political influences of Euro and the equivalent USA guidelines. That's probably no bad thing given the depletion of natural resources and western economies exposure to producers, even if you cannot accept the global warming argument (of which I agree there is good reason to question or even retain an amount of cynicism).

Sorry to rant, but I absolutely loathe the smelly, dirty, toxic emissions from diesel engined vehicles: When was the last time you switched the recirculating air button behind a petrol engined car? (Unless it was burning oil just before it broke down)

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Well it does smack of a rant, or perhaps a justifaction for what strikes me as the relatively pointless development of hybrid drive trains. But isn't the objective of current government policy to encourage us into using "smaller" more fuel efficient cars? The day that petrol does this cheaper than diesel is the day when the diesel market will decline.

I don't believe the description of diesels as smelly, dirty and toxic is a demonstrable reality. Neither would it seem do millions of other car buyers.

But personally, if I was about to change my work car, I would now consider buying a small petrol driven car because thay are quiet, economical and tax efficient. Then again I am lucky enough to have some other options to brighten up the day. 8)

Just looked at 3-series and the difference is even more marked:

Model OTR Price Fuel BIK (%) CO2 (g/km) Combined fuel consumption (mpg) Power Output (hp) 0-62mph (secs)
325i SE £26,585 Petrol 21% (21%) 170 (170) 39.8 (39.8) 218 6.7 (7.1)
330d SE £30,395 Diesel 22% (25%) 160 (175) 46.3 (42.8) 231 6.7 (6.8)

So for exactly the same acceleration you save nearly £4k at purchase, 1% BIK (but on a lower figure) and fuel consumption is just 16% worse (about 1.5p per mile)

I do have a prejudice against diesel, it is really nasty stuff from a health point of view - not just the toxic emissions, but also killing motorcyclists and wildlife through spillages. But what really gets to me is that the almost total switch to diesel is based upon mis-information and misunderstanding.

With regard to hybrids, I agree that in their current form they are not viable as a long term solution to the sustainability issue (but I personally, would still rather that than a diesel). However, it is almost certain that future sustainable cars will drive the wheels via electric motors and a hybrid is the first step towards developing that technology - you then just need to find an alternative power/battery charge source to the existing petrol engine.

We have an Audi A8 4.2V8 petrol, and I recently test drove an A8 3.0tdi.

I was amazed by how grunty the diesel felt- no slower in day to day driving, and it returned 38mpg where ours would have done around 23. It seemed to waft along in a more relaxed way on the torque.

Admittedly, the diesel didn't sound as good, as was a little thrummy at tickover, but that is a huge saving in fuel economy with no performance penalty.

Taken a stage further, the 4.2v8 petrol A8 is actually slower than the 4.2V8 diesel.

Robertb said:

We have an Audi A8 4.2V8 petrol, and I recently test drove an A8 3.0tdi.

I was amazed by how grunty the diesel felt- no slower in day to day driving, and it returned 38mpg where ours would have done around 23. It seemed to waft along in a more relaxed way on the torque.

Admittedly, the diesel didn't sound as good, as was a little thrummy at tickover, but that is a huge saving in fuel economy with no performance penalty.

Taken a stage further, the 4.2v8 petrol A8 is actually slower than the 4.2V8 diesel.

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OK, look at this another way - if there was absolutely no financial or political advantage behind either choice, but purely the car that you would rather drive, which would you buy?

Wattie said:

Robertb said:

We have an Audi A8 4.2V8 petrol, and I recently test drove an A8 3.0tdi.

I was amazed by how grunty the diesel felt- no slower in day to day driving, and it returned 38mpg where ours would have done around 23. It seemed to waft along in a more relaxed way on the torque.

Admittedly, the diesel didn't sound as good, as was a little thrummy at tickover, but that is a huge saving in fuel economy with no performance penalty.

Taken a stage further, the 4.2v8 petrol A8 is actually slower than the 4.2V8 diesel.

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OK, look at this another way - if there was absolutely no financial or political advantage behind either choice, but purely the car that you would rather drive, which would you buy?

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Diesel :wack: :frustrated: :starwars: :gunfire:








:floor: :floor: :hand: