Say, what's the difference between a diesel and a petrol car anyway?

DoubleBogey · 04-04-2011 08:08PM

Hi guys,

I'm about to order a new ford focus and am trying to decide on its configuration. I currently own a mk2 1.6L petrol and have literally had absolutely no problems whatsoever. Unfortunately, practicality comes into play and I need 4/5 doors and a bigger boot, so I'm trading up. The only reason I'm even considering a diesel is because everyone is getting them, so I was thinking I must be missing a trick here. But this thread has sort of reconfirmed what I had always thought, that petrol is better than diesel and diesels are unreliable and expensive to maintain (?!) But having said that, there isn't even a petrol focus to test drive. They're all low end diesels (95 bhp). So if they're so bad then why has the world gone diesel? Is it purely for the lower CO2 emissions? There has to be more to it surely?!

Going by the spec brochure, the 95 bhp diesel is slightly slower off the start compared to my petrol 1.6 but faster between 50-100kph. When I test drove it the noise levels were very low compared to my mk2 petrol and the sales guy says the new diesels are just as reliable and only require a service every 20k km, same as my mk2 petrol. I couldn't get a decent run on the test drive, so don't really have a proper feel for it. I did think it was strange that I had to change into 2nd gear almost immediately because the power just hit a brick wall, I'm guessing that's an indication of whats being said on here about needing constant gear changes. But overall, going around at 60-70kph in moderate traffic, I can't say I was disappointed with it. Likewise I can't really say I was overally impressed with it either.

I just can't decide. My head is wrecked! Please give me some advice! I do a mixture of motorway and city driving on a daily basis. I'm not looking for lots of power, but it should definitely have enough power for the make of the car. i.e it needs to be thereabout with my current 1.6L petrol.

Thanks

Matt Simis · 04-04-2011 08:13PM

tossy wrote: »

thats why i'd never drive a 4 pot diesel again! The 6 pot diesel engine still has a narrow power band compared to a similar petrol engine but the difference over a 4 pot is night and day as long as you can't hear it ticking over

Im not comparing it to a 4pot! Im comparing to a 5pot CR engine and a 6pot CR engine. No matter how much worse the 4pots are, they all have by design a super narrow powerband. Its not a question of cylinders.
The 5pot in question has a larger powerband than the older designed PD VAG 2.5V6, more powerful/tunable (than some of them anyway, there are like 3 VAG 2.5s?) and Common Rail, therefore smoother and more petrol like.

challengemaster · 04-04-2011 08:18PM

DoubleBogey wrote: »

So if they're so bad then why has the world gone diesel? Is it purely for the lower CO2 emissions? There has to be more to it surely?!

Realistically, there's about a handfull of people who actually care about the CO2 emissions. What they do care about are tax bands, better MPG and cheaper, more economical fuel. If you're doing enough driving so that diesel will save you 30-40+ quid a week then its an obvious choice

DoubleBogey · 04-04-2011 08:32PM

challengemaster wrote: »

Realistically, there's about a handfull of people who actually care about the CO2 emissions. What they do care about are tax bands, better MPG and cheaper, more economical fuel. If you're doing enough driving so that diesel will save you 30-40+ quid a week then its an obvious choice

OK, the economics are also important to me. But I do not find my current petrol engine (1.6l 105bhp) to be uneconomical. I do approx 55km a day, except on weekends which can vary between 0km and 50km a day. At the moment I spend €40 per week on petrol. Can I expect much more of a saving on that if I go diesel? Difference in road tax is €50, not really a deciding factor for me.

C4Kid · 04-04-2011 08:51PM

there isn't even a petrol focus to test drive. They're all low end diesels

My uncle was telling me something similar & only the Ka and some Fiestas come in petrol.

If all manufacturers produced mainly Diesel cars than the demand will surely push up the price and in time wipe out any short-term saving.

DoubleBogey · 04-04-2011 09:05PM

C4Kid wrote: »

My uncle was telling me something similar & only the Ka and some Fiestas come in petrol.

If all manufacturers produced mainly Diesel cars than the demand will surely push up the price and in time wipe out any short-term saving.

Well the 1.6l 125 bhp is already cheaper than the 95bhp diesel.

Bigus · 04-04-2011 11:33PM

Try a Kia Ceed diesel 1.6 or petrol !

challengemaster · 05-04-2011 01:21AM

55km a day you wont see the benefit of it

Dartz · 05-04-2011 03:01AM

Was driving a Renault Scenic 1.5dci recently.

Was just going to overtake on the M3. Put foot down in top gear, thinking it was spinning fast enough to pull.

Sure the noise increased, but the speed didn't. Had enough time to turn to the cars owner and ask why it wasn't going before it finally picked up and went.

Felt like the thing was looking at me... "Non, not before I finish zis cigarette,"

BigDuffman · 05-04-2011 01:08PM

Onkle wrote: »

And you Tdiddly VAG heads slag off us VTEC YO drivers

For us laymen

:p

dharn · 05-04-2011 01:23PM

if you compare the 06 bmw 320d and 320i the diesel beats it in all categories 0-60 mpg 30-70 etc diesel less revvy and a bit of turbo lag if driving in 6 gear coming to roundabout i find you have to change back to 4 to have any acceleration but from 1600 revs up massive torque had 3 318 petrols before 320d and really prefer 320d

Max Power1 · 05-04-2011 01:50PM

And reverse that graph for most diesels!

05-04-2011 01:57PM

dharn wrote: »

if driving in 6 gear coming to roundabout i find you have to change back to 4 to have any acceleration

Surely you wouldn't negotiate a roundabout in 6th? You should be ready to stop on the approach to one.

professore · 05-04-2011 02:06PM

As someone who has ALWAYS driven diesels .... (except motorbikes

)

It seems there are a lot of Jeremy Clarkson petrol heads on here trying to make out nothing ever goes wrong on a petrol car but every diesel explodes.

I find them very reliable overall, and definitely more fuel efficient than equivalent size petrol car. Having said that the newest one I had was a 1.4 HDi Peugeot 206 (02 model). The others were variants of the old non-common rail diesel peugeots and those things are impossible to kill. The 1.4 HDi I put 30K miles on it and other than standard maintenance (including replacing the timing belt) I had no issues at all.

I have driven petrol cars on occasion, and my experience is that you have to rev the c**p out of them to get them to move. If you like relaxed driving, i.e. not going 0-60 in 2 seconds from the traffic light, but rather nice smoooooth progress, get a diesel. Otherwise get a petrol.

Joe 90 · 05-04-2011 02:12PM

challengemaster wrote: »

Realistically, there's about a handfull of people who actually care about the CO2 emissions. What they do care about are tax bands, better MPG and cheaper, more economical fuel. If you're doing enough driving so that diesel will save you 30-40+ quid a week then its an obvious choice

I reckon that if you drive a lot, always going to be driving a car that is under guarantee the a diesel may well make sense. If you don't do a lot of mileage and have to foot the bills yourself then petrol seems to make more sense.
My logic is based on the fact that to save money with a diesel you need to do a fair mileage to cover the initial cost difference and while they probably don't really give expensive trouble that often the fact is that when they do expensive means expensive.

Bigus · 05-04-2011 02:16PM

professore wrote: »

As someone who has ALWAYS driven diesels .... (except motorbikes )

I find them very reliable overall, and definitely more fuel efficient than equivalent size petrol car. Having said that the newest one I had was a 1.4 HDi Peugeot 206 (02 model). The others were variants of the old non-common rail diesel peugeots and those things are impossible to kill. The 1.4 HDi I put 30K miles on it and other than standard maintenance (including replacing the timing belt) I had no issues at all.

I have driven petrol cars on occasion, and my experience is that you have to rev the c**p out of them to get them to move. If you like relaxed driving, i.e. not going 0-60 in 2 seconds from the traffic light, but rather nice smoooooth progress, get a diesel. Otherwise get a petrol.

I really like the way modern diesels give you a shove in the back from all the torque which can mean having some fun without losing your licence.

I was actually disappointed driving an Audi RS4 V8 because it needed to be wrung out rather than having the shove of a Remapped TDi

The point i was making earlier is that old diesels used to go forever 300D et all,
But i don't think people realise how highly explosive modern diesels are and the bills that go with these malfunctions particularly when injectors and pumps are machined to NANO spec literally

Matt Simis · 05-04-2011 02:18PM

professore wrote: »

As someone who has ALWAYS driven diesels .... (except motorbikes )

It seems there are a lot of Jeremy Clarkson petrol heads on here trying to make out nothing ever goes wrong on a petrol car but every diesel explodes.

If you like relaxed driving, i.e. not going 0-60 in 2 seconds from the traffic light, but rather nice smoooooth progress, get a diesel. Otherwise get a petrol.

I think as someone with a bias'ed and blinkered view you cannot make a genuine comment on this topic at all. Obviously.
The fact you accuse everyone else of Clarksonism yet end your post on an illogical and factually incorrect soundbite is deliciously ironic.

Bigus wrote: »

I was actually disappointed driving an Audi RS4 V8 because it needed to be wrung out rather than having the shove of a Remapped TDi

Good god! :eek:

05-04-2011 02:22PM

professore wrote: »

If you like relaxed driving, i.e. not going 0-60 in 2 seconds from the traffic light, but rather nice smoooooth progress, get a diesel.

Or get a decent petrol

My ZT makes smoooooooooooth progress even though it's archaic :pac:

professore · 05-04-2011 02:27PM

Matt Simis wrote: »

I think as someone with a bias'ed and blinkered view you cannot make a genuine comment on this topic at all. Obviously.
The fact you accuse everyone else of Clarksonism yet end your post on an illogical and factually incorrect soundbite is deliciously ironic.

What's incorrect about it? I have seen nothing except petrol = good, diesel = bad from many posters. This is not true. It's horses for courses. Maybe the newer ones explode but as I said, I had a "newer" one for 30K and it didn't explode. Lots of petrol cars have expensive failures too. Please provide stats showing that diesels are more unreliable than petrols. I'm not saying they're not, I would just like to see the unbiased stats.

05-04-2011 02:34PM

professore wrote: »

Please provide stats showing that diesels are more unreliable than petrols.

He's not the CSO :pac:

professore · 05-04-2011 02:36PM

RoverJames wrote: »

He's not the CSO :pac:

Asserting something without evidence to back it up is worthless.

05-04-2011 02:46PM

Ok, modern diesels have DMFs, most petrol don't. DMFs fail.
Modern diesels have DPFs, petrols don't DPFs fail.

When there are more failure modes the chance of failure is greater.

30k miles in a 307 is hardly a great survey, can we bin your comments so?

Matt Simis · 05-04-2011 02:55PM

professore wrote: »

What's incorrect about it? I have seen nothing except petrol = good, diesel = bad from many posters. This is not true. It's horses for courses. Maybe the newer ones explode but as I said, I had a "newer" one for 30K and it didn't explode. Lots of petrol cars have expensive failures too. Please provide stats showing that diesels are more unreliable than petrols. I'm not saying they're not, I would just like to see the unbiased stats.

Um.. Im not providing stats as Im not the one that said diesels are more or less reliable and that wasnt what I replied to you about. Infact my only "reliability" comment was that the Swirl flap failure on BMW diesels was actually very rare and already fixed (ie supporting your point).

My comment to you was you started your post proclaiming your body of knowledge and preference are exclusively Diesel. That makes anything you say afterwards pure bias.

Finally the "incorrect" bit I referred to was about the "smoothness" of diesels and the idea that petrols are for people that street light drag race. Thats complete rubbish, diesels are not in any manner "smooth" or refined. CR is more refined than Indirect Injection diesel yes, but still miles from petrols. Proper petrol engines dont need to be driven hard to be smooth, you would know this is your werent all about 4pot little diesels.

professore wrote: »

Asserting something without evidence to back it up is worthless.

Again, Im not the poster making assertions pro or con reliability, you and Bigus are.
The diesels I have had, drive regularly and now own were/are far smoother and better than the 1.4HDi engines you are harping on about anyhow.

Gary ITR · 05-04-2011 03:22PM

LIGHTNING wrote: »

Here is my crude graph to explain.Its the torque vs RPM of a Honda engine :pac:

http://img263.imageshack.us/i/vtecr.jpg

I'll drive it over your foot now!

I'll have you know my car makes smooth poor the whole way up :pac:

spiggotpaddy · 05-04-2011 03:30PM

professore wrote: »

What's incorrect about it? Please provide stats showing that diesels are more unreliable than petrols. I'm not saying they're not, I would just like to see the unbiased stats.

sure stats can be used to prove anything.
40% of all people know that.

Gary ITR · 05-04-2011 03:34PM

spiggotpaddy wrote: »

sure stats can be used to prove anything.
40% of all people know that.

93% of all stats are made up

EPM · 05-04-2011 03:49PM

professore wrote: »

Asserting something without evidence to back it up is worthless.

Your basing you assumption on exclusively diesel driving. Ignoring the obvious limitations of that assumption, you have also said the oldest diesel you drove was a 2002.

Since then diesels have been subject to more stringent emissions regulations. They are now fitted with diesel particle filters as a result. These are known to clog when used for mostly city driving. A common fault across all manufacturers. Another issue is dual mass flywheels - not exclusively a diesel fitment but are still known to fail relatively regularly on higher mileage diesels.

I dont have figures to back any of this up but try searching here for a petrol dmf failure or indeed a petrol (:D) dpf failure.

Max Power1 · 05-04-2011 04:09PM

EPM wrote: »

a petrol (:D) dpf failure.

Its a known fact that no DPF has ever been failure free in a petrol engine.

05-04-2011 04:15PM

EPM wrote: »

Another issue is dual mass flywheels - not exclusively a diesel fitment but are still known to fail relatively regularly on higher mileage diesels.

....... and lower mileage ones too

EPM · 05-04-2011 04:26PM

Max Power1 wrote: »

Its a known fact that no DPF has ever been failure free in a petrol engine.

RoverJames wrote: »

....... and lower mileage ones too

Rare but does happen for sure. Probably more likely a manufacturing fault on very low mileage ones.

Say, what's the difference between a diesel and a petrol car anyway?

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