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      07-18-2012, 10:51 AM   #1
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Interesting Article Regarding The Cost Benefits Of Petrol V Diesel Cars

http://www.dailymail.co.uk/news/arti...st_read_module
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      07-18-2012, 12:27 PM   #2
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They completely ignore the fact that diesel residuals are often a lot better and maybe even a wider gap than the difference at new.
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      07-18-2012, 02:24 PM   #3
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thats the daily mail for you...

I agree on the residual front. Which is why buying a used petrol makes even more sense!
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      07-18-2012, 02:45 PM   #4
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I bought a diesel 335 not because of economy but because of residuals as big petrols are so hard to shift. Also after experiencing the immense torque I was won over easily.
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      07-18-2012, 03:02 PM   #5
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This debate has been done a few times on here recently.

In my experience the problem with all these comparisons is that in a diesel you can actually achieve the quoted MPG, or more importantly, get close to it in spite of having a slightly heavy right foot.

In a petrol, unless you drive like Grandma ALL the time, you can't get anywhere near it. All the petrols I've had for any length of time have realistically got me high 20s -very low 30s MPG, when their quoted figures were 36+
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      07-18-2012, 03:07 PM   #6
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I know we can't look at purchase costs and fuel savings as the only factors, but do feel as supply and demand changes due to a flooded used diesel market, residuals will likely take a knocking.

I'm already aware of folks moving back to petrol (partly as petrol engines are becoming more efficient) and the true cost of maintaining older diesel engines hits the attention of the used market. Many have been stung with poor diesel economy against 'promised' consumption, but also turbo, EGR, injection and DPF failures, big bills leave a bad taste. It is only the view, (or perception) of the used market that holds up, or drops the value out of residuals.

The AA have done a lot of research on running costs and their figures also reflect the narrowing gap, including allowing for current diesel residuals.

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      07-18-2012, 03:17 PM   #7
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I saw that article earlier. It's a complete farce.

Comparing the 328i (4pot 2.0l) against the 330d (6pot 3.0) and the 1.4 petrol astra against the 2.0 derv.

But its the mail so what else can you expect. Celebrity gossip junk and articles copy/pasted from other newspapers.
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      07-18-2012, 03:21 PM   #8
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Quote:
Originally Posted by chris_s1 View Post
In my experience the problem with all these comparisons is that in a diesel you can actually achieve the quoted MPG, or more importantly, get close to it in spite of having a slightly heavy right foot.
I'm not so sure that is strictly true, as diesel becomes more inefficient as you work them hard, particularly if high revs are used. Whereas the throttled petrol engine is less inefficient with higher revs and lower pumping losses.

A lot of how mpg figures, has to do with engine size. I've always found it easier to achieve excellent mpg with big petrols, rather than smaller petrol engines. The new generation of small diesels are poor in real world driving and have huge mpg shortfall. Even the mid range diesels are falling into negative figures. Now way past 15% shortfall, as an average.

But it is a big subject and user perceptions are still wide apart.

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      07-18-2012, 03:29 PM   #9
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That's not my experience. I do 30k/yr and have had various diesels and petrols.

My last company car was a dreadful Passat 1.9tdi and that spent the majority of its life on full throttle (and a lot at high revs as it had a stupid 5 speed box) and it still managed over 40mpg over 50k miles.
I then had a Saab 2.0 petrol for a few months and drove at a similar pace (obviously driving it much less hard to achieve the same results) and got something like 25mpg over 20k.

My 325d I had long term before my current car got over 40mpg over its life, despite me driving it pretty hard. My wifes Qashqai petrol struggles to get in the 30's most of the time, driven the same way, despite a quoted 38mpg (I think)
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      07-18-2012, 03:53 PM   #10
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Quote:
Originally Posted by chris_s1 View Post
That's not my experience. I do 30k/yr and have had various diesels and petrols.

My last company car was a dreadful Passat 1.9tdi and that spent the majority of its life on full throttle (and a lot at high revs as it had a stupid 5 speed box) and it still managed over 40mpg over 50k miles.
I then had a Saab 2.0 petrol for a few months and drove at a similar pace (obviously driving it much less hard to achieve the same results) and got something like 25mpg over 20k.

My 325d I had long term before my current car got over 40mpg over its life, despite me driving it pretty hard. My wifes Qashqai petrol struggles to get in the 30's most of the time, driven the same way, despite a quoted 38mpg (I think)
I'll go along with what you are reporting, the VAG 1.9TDI is one of the best and efficient diesel engines ever made, brilliant BSFC for that engine. But a 2.0 petrol in a Saab, oh dear, a very thirsty setup. (But as a side comment, the 1.9TDI in a B5 Passat is a 60mpg motor, driven sensibly).

Your other example in the Qashqai, again not known to be an economical set up, so yes you prove you point.

But for me, my BMW 540i touring, returned 27mpg over 45k miles. Well above the 21mpg combined figure. Current 330d touring (driven as the 540i) just about equals the combined figure of 37.1mpg, returning 37mpg over 53k miles. I expected more as an average, from the diesel, but it just doesn't work at the same driving pace as the big petrol. Back off and yes it will climb.

I've many other examples, but it follows a similar pattern. What we find often depends on whether we have examples that typically are known for good (or bad) consumption, that are pitched against each other.

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      07-18-2012, 03:59 PM   #11
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Part 2 of the article will be how diesel cars cause cancer.
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      07-18-2012, 04:08 PM   #12
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When you drive diesel cars faster they drink the juice too. There isn't any way around that.

From what I read from many guys on here many of the 335d drivers get very low 30MPG. Did Carlos, who did thrash his, not claim his overall average was something like 16MPG in his 335d?

Guys with the 330d often report it as an achievement to break 40MPG on a run.

I've owned quite a few diesels and they all needed nursed to get anywhere near the claimed figures just like a petrol. Are they not tested in the same circumstances?

Not sure why anyone can be shocked by the results. Many better magazines have carried out the same feature for years and keep coming up with the same results.

Unless you do very big miles, I can't see any reason to buy any diesel over a petrol equivalent. Too many people needlessly driving cement mixers.
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      07-18-2012, 04:32 PM   #13
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Quote:
Originally Posted by Kerr View Post
Too many people needlessly driving cement mixers.
Cement mixers!

Fecking cheek - tractors, please.
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      07-18-2012, 04:44 PM   #14
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Quote:
Originally Posted by Kerr View Post
When you drive diesel cars faster they drink the juice too. There isn't any way around that.
Here's something I posted a few years back.

Quote:
How about this… Autocar 535d Road Test.

Model : 2005 e60 535d
Fuel : Diesel
Transmission : 6 speed auto
Driving Norm : Road/Performance Testing
Driving Style : “How fast does this thing go?”
MPG : Official Combined 35.3mpg, Road Test 13.2mpg

Yes… “13.2MPG” that’s drinking some diesel. The M6 which has a combined consumption of 14.8mpg returned 11.1mpg in road/performance testing by Autocar. Tells us something about plummeting fuel consumption when we drive a diesel hard.
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      07-18-2012, 04:56 PM   #15
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Quote:
Originally Posted by The_Bear_Yid View Post
Part 2 of the article will be how diesel cars cause cancer.
W.H.O (World Health Organization) have recently published a report where they clearly state the carcinogenic (cancer) risk from diesel fumes. Aimed more at its total use in industry (and mining in particular), but still a killer all the same, from our use in cars.

One report of it, from NY Times.

http://www.nytimes.com/2012/06/13/he...-who-says.html

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      07-18-2012, 04:57 PM   #16
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Quote:
Originally Posted by HighlandPete View Post
Here's something I posted a few years back.



HighlandPete
All you have to do is read the trip computer when you put your foot down.

Every reasonable diesel I've driven when you put the foot to the floor it reads around about 10MPG.

It all matters how long you keep your foot on the floor that matters.

It is just another of those driving myths like when diesel drivers used to think it was safe for them to drive through deep puddles.
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      07-18-2012, 05:00 PM   #17
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'tis true.

Diesels are ridiculously efficient under light load - which is why repmobiles that only do thousands of motorway miles get such great returns. Start accelerating and asking the engine to shift 2 tonnes of car from stationary and the economy plummets.

Of course the same principle applies with petrol engines, but less extreme.
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      07-18-2012, 05:01 PM   #18
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Quote:
Originally Posted by Kerr View Post
When you drive diesel cars faster they drink the juice too. There isn't any way around that.

From what I read from many guys on here many of the 335d drivers get very low 30MPG. Did Carlos, who did thrash his, not claim his overall average was something like 16MPG in his 335d?

Guys with the 330d often report it as an achievement to break 40MPG on a run.

I've owned quite a few diesels and they all needed nursed to get anywhere near the claimed figures just like a petrol. Are they not tested in the same circumstances?

Not sure why anyone can be shocked by the results. Many better magazines have carried out the same feature for years and keep coming up with the same results.

Unless you do very big miles, I can't see any reason to buy any diesel over a petrol equivalent. Too many people needlessly driving cement mixers.
Oh yeah, if you do drive the big diesel fast of course it will drink the juice. However, drive it sensibly, and you can often get good returns.

I have had many different cars, petrol and diesel, and here is what I found:

Audi A3 2.0 TDI 140 BHP remapped to about 170 BHP: 45-47 mpg over 50k.
Audi A4 2.0 TDI 143 BHP : 40 mpg over 20k
Audi A4 2.0 TDI 177 BHP : 37 mpg over 3.5k (got rid as thats appauling for a diesel).

VW Golf 1.8T tuned to 240 BHP : 28 mpg over 30k
VW Golf 2.8 V6 204 BHP: 26 mpg over 10k
Audi S4 4.2 V8 345 BHP : 23 mpg over 8k

Now I have my BMW 335d, remapped to 330-340 BHP

So I have only done 2 tanks in this motor so far. Averaging 37.5 mpg overall.
BUT, I did give it a go to see what I could expect to get if I tried, and on a 25 mile run, with approximately 8 miles town, 10 miles dual carriageway, and 7 miles of A road, I averaged just over 45 mpg.

Still, considering it is similar power output to the S4, the 15 mpg extra I get is very welcome. It has around double the power of my old A3, and I CAN, if I wished, get a similar consumption figure to the overall I got in that car.

These results are accurate brim to empty calculations, taken from a variety of cars, over 120-odd thousand miles. With the same driver, driving the same way, over the same roads. So a fair evaluation of the difference between petrol and diesel cars.

I think it is fair to say that diesel is still more economical than petrol, and while you may pay a premium for the diesel engine when you purchase it, you do get a lot of it back in residual value at the end. As well as it being a much easier sell. My S4 was for sale for 18 months before it finally sold. And the price was dropped by over 30% to get it away too.
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      07-18-2012, 05:40 PM   #19
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Diesel is obviously more fuel efficient, due to thermal efficiency of the engine. But what is clear, the gains are not the magical figures many believe a diesel will return.

Diesel needs to be run light and near constant speeds to get the best returns. My son drove his car (A3 140 TDI S-line) back from Inverness the other day in slow traffic and the OBC was showing 68.3mpg after 75 miles. But drive it normally and it is well short of the combined figure, even in easy conditions.

Now go back a few years and a VW Golf Mk4 GT 1.9 TDI would easily return more than 10% above the combined figure in real world driving, without effort. We'd see 75mpg from the Golf TDI on easy runs. It was a 60+mpg car long term.

Latest emission controls and fuel quality/specification (ULSD) means we just don't get the results, even with all the ECO aids, unless we now drive like Grandma. It is this factor, among others, which is allowing the petrol to claw back some of the disadvantage it showed a few years back.

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      07-18-2012, 06:06 PM   #20
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I've done my fair share of ragging hire cars and I always find the petrols are a lot thirstier when being strangled.
I had a 1.6 diesel Focus one week and the thing rarely left the redline and it still managed 40mpg~.
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      07-18-2012, 09:39 PM   #21
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Quote:
Originally Posted by HighlandPete View Post

I'm already aware of folks moving back to petrol (partly as petrol engines are becoming more efficient) and the true cost of maintaining older diesel engines hits the attention of the used market. Many have been stung with poor diesel economy against 'promised' consumption, but also turbo, EGR, injection and DPF failures, big bills leave a bad taste.

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I hope they are not moving back to BMW petrol in an effort to save of maintenance costs, as I can't see them being any less complex than equivalent diesel.
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      07-19-2012, 02:00 AM   #22
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I bought my diesel 320D auto rather than a petrol 320i auto because of its much superior performance. Its extra cost is also good value for money.
The better fuel consumption is a useful bonus!
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