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

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I don't know anything about cars, at all, and I've been struggling to find answers to the following questions online:

"In layman's terms, what is the difference between a diesel engine and a petrol engine in a car and what are the pros and cons for each?"

Thanks for reading.

Mr Benevolent

Diesel

Pros: Much more efficient, more torque.
Cons: Less horsepower compared to an equivalent petrol, more complex, slightly less reliable, slightly more challenging to drive on.

Petrol:

Pros: Best engine response and drivability, less complex.
Cons: Less efficient, less torque.

Note: All of these pros and cons are currently being heavily blurred!

Confab

Confab wrote: »

slightly more challenging to drive on.

That's a new one for me.

pippip

Petrol is generally quieter

Leonard Hofstadter

Petrols handle better because there is less weight over the front wheels.

They usually sound much nicer too.

If it wasn't for VRT, they would be cheaper to buy.

Diesels have the advantage of superior resale value and lower tax as well.

However, they do not take very well to being driven mostly around town, you are likely to get DPF failure pretty quickly.

They usually run at much lower revs so are quieter on motorways and dual carriageways than petrols too.

Gophur

www.howstuffworks.com

EPM

RoverJames wrote: »

That's a new one for me.

Reckon it's something to do with turbo lag. Can be a right pain in the backside at times...

Ah the lag the lag
Can't say I ever found it a bother in any diesel I drove, from non intercooled Rovers to new Insignias or A3s. It's defo there though, no dount about that.

EPM

RoverJames wrote: »

Ah the lag the lag
Can't say I ever found it a bother in any diesel I drove, from non intercooled Rovers to new Insignias or A3s. It's defo there though, no dount about that.

2nd gear, 1500 revs...wait for it...2000 revs...still waiting...2500 revs wheelspin:mad:

Stupid diesels:pac:

bazz26

EPM wrote: »

2nd gear, 1500 revs...wait for it...2000 revs...still waiting...2500 revs wheelspin:mad:

Stupid diesels:pac:

Maybe on some VAG diesels but not all diesels.

EPM

bazz26 wrote: »

Maybe on some VAG diesels but not all diesels.

Hence the need for a remap to sort out the power delivery;)

Not as sudden as the PD and fine in every other gear really but is a real PITA around town or on smaller slip roads.

spiggotpaddy

Waylon Weak Ration wrote: »

I don't know anything about cars, at all, and I've been struggling to find answers to the following questions online:

"In layman's terms, what is the difference between a diesel engine and a petrol engine

Thanks for reading.

the main difference between the engines is the fuel ignition, petrol engines use
an electric spark to ignite a highly refined fuel at relativley low compression

where as diesel engines use heat created by very high compression to ignite
a less refined fuel oil.

Gary ITR

EPM wrote: »

2nd gear, 1500 revs...wait for it...2000 revs...still waiting...2500 revs wheelspin:mad:

Stupid diesels:pac:

And you Tdiddly VAG heads slag off us VTEC YO drivers

EPM

Onkle wrote: »

And you Tdiddly VAG heads slag off us VTEC YO drivers

Ah sure that's only masking our own insecurities:D:p

PaulKK

bazz26 wrote: »

Maybe on some VAG diesels but not all diesels.

Amen to that bazz.

EPM wrote: »

2nd gear, 1500 revs...wait for it...2000 revs...still waiting...2500 revs wheelspin:mad:

Stupid diesels:pac:

Or else 1500 RPM... Woosh

Matt Simis

Onkle wrote: »

And you Tdiddly VAG heads slag off us VTEC YO drivers

Turbo diesels is like VTEC minus the fun and with the Rev range in Reverse.
Not that fast to just under 2000rpm, then 90% of the engine torque "happens" and is effectively over by 3500rpm. Yes our current diesel will rev to over 5000, but there is little benefit (and FWIW the common VAG diesels arent that great in anything but economies of scale).

The longer you hold down the pedal in a diesel the more "diminished" the power available is. The longer you hold down the pedal in a petrol, the higher the revs climbs and the faster you go.

The diesel has a narrow powerband, the annoyance of "driving on" a diesel is the fact you have to shift gears continiously to keep it in 2000-3000 rpm. I remember the "old" arguments we used to have on Boards where people said diesels dont need to shift as much as petrol. Complete BS, diesels need to shift far far more than a petrol. Both types of Combustion engines have gear boxes for exactly the same reason, however the power band size determines the amount of shifting to keep in the sweet spot. Diesels have a small powerband.

Now if you have a 6speed (or 7/8speed in latest diesels) Automatic box with fast shift times, it can make a huge difference to the drivability of a diesel. I think something like the new BMW F10 535d with the 8speed gearbox would "feel" like it has mountains of smooth power.

_Kaiser_

Ah but you learn to adjust to the lag... remap does help though - but then you need to remember that too.

Light's green at short-sequence junction, foot down.. loud rumble, wheelspin, movement...

Great on motorways tho!

Bigus

I don't think people realise how much expensive trouble modern high pressure diesels are giving in the real world.

Modern diesels inject at up to 18000 psi with dire consequences when things go wrong
Examples

Avensis injectors € 4k



Renault injector pumps if you put petrol in ???? 2-3 K

TDCI fords faulty injectors burn holes in pistons 4.6K for a short block.

Passat diesels Computer troubles and particulate filters

Lexus 220d burning oil 7K

BMW diesels suck in swirl flaps new engine 7k

Along with dmf, egr, and now particulate filter problems !!!!!!!!!!!!

Skoda & Hyundai dual mass flywheels € 2.5 K

Also on all brands any misfire usually results in bills for thousand rather than hundreds.

A few quid extra on petrol every week can be a huge saving in the long run

Matt Simis

Bigus wrote: »

BMW diesels suck in swirl flaps new engine 7k

In fairness thats an extremely rare occurrence and eliminated post 2005 on all models.

CarMuppet

To OP: diesel engines can burn agri-fuel.... petrol ones can't..... sorry only joking. Honest.

I think wikipedia can explain a lot more than you'll get from this thread tbh.


http://en.wikipedia.org/wiki/Diesel_engine

http://en.wikipedia.org/wiki/Petrol_engine

biko

If you intend to drive mostly around the country - diesel.
If you intend to drive mostly around the town - petrol.

_Kaiser_

Bigus wrote: »

Passat diesels Computer troubles and particulate filters

You left out the now infamous "injector failures" on early 2.0 TDI (05-07/8 era) Passats, €1k a piece and generally the rest seem to fail not long after the first.

Apparently it's great fun when it happens on a motorway, because the computer just shuts off the power completely! :eek:

Gather it's resolved with the newer CR engines (08 onwards)

I keep expecting my own 06 2.0 TDI to go (with 162000km and rising on the clock) but so far - **bangs on the wooden desk** - it hasn't misbehaved.
I DID have to replace the DMF though before Xmas (another €1000), but since then it's been running fine! (serviced on time and at a main dealer )

Cookie_Monster

Petrol = good
Diesel = bad

:D:D

Bigus

Kaiser2000 wrote: »

You left out the now infamous "injector failures" on early 2.0 TDI (05-07/8 era) Passats, €1k a piece and generally the rest seem to fail not long after the first.


I DID have to replace the DMF though before Xmas (another €1000), but since then it's been running fine! (serviced on time and at a main dealer )

My whole point another €1000


I left out loads of car problems that I don't have concrete info on for fear of being lynched here.

I never mentioned turbo problems which is universal on all brand Diesels

gyppo

Matt Simis wrote: »

The diesel has a narrow powerband, the annoyance of "driving on" a diesel is the fact you have to shift gears continiously to keep it in 2000-3000 rpm. I remember the "old" arguments we used to have on Boards where people said diesels dont need to shift as much as petrol. Complete BS, diesels need to shift far far more than a petrol. Both types of Combustion engines have gear boxes for exactly the same reason, however the power band size determines the amount of shifting to keep in the sweet spot. Diesels have a small powerband.

I think driving styles have a lot to do with this too. Many diesels suit lazy drivers (like me) who are happy to let the low down torque of the oil burner pull it around at 1500rpm or so, rather than changing down gears in a petrol engined version.

Matt Simis

gyppo wrote: »

I think driving styles have a lot to do with this too. Many diesels suit lazy drivers (like me) who are happy to let the low down torque of the oil burner pull it around at 1500rpm or so, rather than changing down gears in a petrol engined version.

True, if you get where you are going without having to change gear, then yeah its good enough. However to change gear at the same pace as a turbo petrol or large CC petrol in a (not slow 200bhp) diesel I need to maybe make 3 gear changes in the diesel vs 1 in the petrol. Its the opposite of "lazy" IMO.

Our Alfa 156 2.4JTD has almost as much torque (300ft/lbs) vs my Audi S8 4.2 V8 (317ft/lbs @ 3400rpm) in a car 400kg lighter yet to overtake at the pace of the Audi.. well its not possible, but to get close to it you need to do some "race" style fast shifting in the Alfa.

bryaner

Cant get out of your face on diesel..:D

Leonard Hofstadter

Bigus wrote: »

I don't think people realise how much expensive trouble modern high pressure diesels are giving in the real world.

Modern diesels inject at up to 18000 psi with dire consequences when things go wrong
Examples

Avensis injectors € 4k



Renault injector pumps if you put petrol in ???? 2-3 K

TDCI fords faulty injectors burn holes in pistons 4.6K for a short block.

Passat diesels Computer troubles and particulate filters

Lexus 220d burning oil 7K

BMW diesels suck in swirl flaps new engine 7k

Along with dmf, egr, and now particulate filter problems !!!!!!!!!!!!

Skoda & Hyundai dual mass flywheels € 2.5 K

Also on all brands any misfire usually results in bills for thousand rather than hundreds.

A few quid extra on petrol every week can be a huge saving in the long run

Don't forget that all PSA 1.6 HDis are not the best with the old DPF either, and also the VAG 2.0 TDI PD can have a defective oil pump which sprays oil all over the engine and results in the engine being a write off!

I agree with you, I'll gladly pay the extra few quid in fuel in the knowledge that the worst I'll get is coil pack or MAF failure and if I'm extremely unlucky I'll get HG failure too.

That said, VW 1.4 TSIs have this habit of lunching their supercharger (and the NA 1.4 is appalling for reliability) and BMWs with Efficient Dynamics have this habit of going through injectors at a rate of knots, so petrol isn't always better

tossy

captainspeed wrote: »

Petrols handle better because there is less weight over the front wheels.

Wow what a sweeping statement of nonsense! Because ALL diesel engines weigh the same i.e heavy and ALL petrol engines are light ? You are taking no account for superior suspension set ups v's crap suspension set ups or 2wd v Awd not to mention engine size!

Matt Simis wrote: »

Not that fast to just under 2000rpm, then 90% of the engine torque "happens" and is effectively over by 3500rpm

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

Cookie_Monster wrote: »

Petrol = good
Diesel = bad

:D:D

exactly! i'm remember this daily when i start my diesel engine.

Owen

EPM wrote: »

Not as sudden as the PD

The who with the what now??

Max Power1

PaintDoctor wrote: »

The who with the what now??

The PD series VAG diesel engines?
I presume thats what he meant?

DoubleBogey

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

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

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

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

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

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

Try a Kia Ceed diesel 1.6 or petrol !

challengemaster

55km a day you wont see the benefit of it

Dartz

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

Onkle wrote: »

And you Tdiddly VAG heads slag off us VTEC YO drivers

For us laymen:p

dharn

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

And reverse that graph for most diesels!

dharn

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

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

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

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

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:

professore

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

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.

professore

professore wrote: »

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

He's not the CSO :pac: