# Diesel vs. Petrol Cars



## Aussiest (21 September 2009)

Hi there,

I am currently considering a new car. What is the deal with diesel vs. petrol in terms of economy & performance? It's a 1.6 litre engine.

I live in the city, so does this factor in (heard diesel is better for long distance)?

To your knowledge, what is the availability of diesel fuel at petrol stations in the city and on the interstate highways (melbourne to sydney, melbourne to queensland)?

Thanks for your comments


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## pointr (21 September 2009)

A complex question on economics and performance. Economics? at times diesel is dearer and at times cheaper than petrol. Diesels can /do get better mileage but how many klms do you do to offset the higher initial purchase price and possibly increased service costs. Performance? diesels of a given size usually develop less Kwt's than petrol but they do develop impressive torque by virtue of a longer piston stroke. It's all 6's and 7's read some motoring tests, take some test drives. Diesel is readily available on major highways,thats what trucks run on, but keep some disposable plastic gloves for refuelling as diesel pumps can be oily.


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## Tysonboss1 (21 September 2009)

Forget Diesel,

Go LPG,

I have run LPG for about 4years now and it has saved me thousands,

you burn about 20% more LPG because it's a lighter fuel, However it's less than half the price of petrol. 

For example my last tank of gas was 50c per litre, add 20% = equals 60c. So it works out at 60c/litre compared to petrol $1.25/litre.

Diesel is more expensive than Petrol in Australia, But I think it lasts longer, but the saving won't be as big as LPG.


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## Aussiest (21 September 2009)

I can't go LPG because the car comes with diesel. Maybe i'll just continue my search until i find a petrol version.


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## gav (21 September 2009)

What car are you loooking at Aussiest?


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## nunthewiser (21 September 2009)

is it a 4wd? . any towing? ,,,,,,,, if so diesel MUCH better . more power for size 


diesel available on all highways ,95% of metro fuel stations 



all depends on what vehicle and what you using it for OZ  and hi


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## Aussiest (21 September 2009)

Hi nun!

And, gav. I'm looking at a Peugot 308 HDI.


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## moXJO (21 September 2009)

Tysonboss1 said:


> Forget Diesel,
> 
> Go LPG,
> 
> ...




Gas pfffttt

If you really wanna save money on gas, get one of these babies


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## nunthewiser (21 September 2009)

Aussiest said:


> Hi nun!
> 
> And, gav. I'm looking at a Peugot 308 HDI.





neat lil car 

the new diesels for normal passenger vehicles are quite good apparently , i know nothing about these , only know about the bigger 4wd diesels ....


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## Glen48 (21 September 2009)

Diesel engine:  change the oil check as required, check the water , Air cleaner look for broken brackets and any damage and forget about it until next time.


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## awg (21 September 2009)

a couple of fairly small matters

bowser rage...not as many diesel vs petrol bowsers, wait 10 mins while a couple of dicks in front fill their Landcruisers 

cant rev high in most diesel engines. not so good for overtaking etc


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## Mr J (21 September 2009)

awg said:


> cant rev high in most diesel engines. not so good for overtaking etc




Revs are irrelevant.


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## Stan 101 (21 September 2009)

Anyways, off topic again but LPG can be a great saving. Even in the north where LPG is about 70-80 cents a litre is is still cheaper. Ford offer an LPG only model with modified cam timing and valves. I could drive from Cairns to Mackay on one tank (75 or 80 litres) with about 50km spare.


cheers,


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## awg (21 September 2009)

Mr J said:


> Revs are irrelevant.




I cannot agree, how are revs irrelevant if you want to overtake, in a manual car, commencing yr OT manouver at about 3500rpm and finishing at (say)5700rpm, without changing gear?

try that in a diesel

(most diesels redline below 5000rpm vs petrol 6000rpm, and their power and torque curve falls away at high rpm, although they are better at low rpm)

I acknowledge that some of the small new diesel engines are much improved in this respect


agree with Stan101, LPG is very economical, and green friendly, just dont run low on LPG in Canberra!


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## marklar (21 September 2009)

awg said:


> I cannot agree, how are revs irrelevant if you want to overtake, in a manual car, commencing yr OT manouver at about 3500rpm and finishing at (say)5700rpm, without changing gear?
> 
> try that in a diesel
> 
> (most diesels redline below 5000rpm vs petrol 6000rpm, and their power and torque curve falls away at high rpm, although they are better at low rpm)




That's why it is important to test drive before you buy a diesel, adjust your driving so you spend most of your time around 1500-2000 rpm and you'll have plenty of 'go' when you need it.  Pick a 2L mk5 diesel Golf and you can overtake pretty much anything on the highway in 5th gear safely, it has THAT MUCH torque  more fun than a GTi

m.


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## Aussiest (21 September 2009)

marklar said:


> Pick a 2L mk5 diesel Golf and you can overtake pretty much anything on the highway in 5th gear safely, it has THAT MUCH torque  more fun than a GTi
> m.




My dad *swears *by those things.

Awg, i'm not a hoon. Just your normal average driver. Do you still think i would have trouble over-taking?

One of the other things that bothers me about a diesel engine is re-sale value / opportunities. I like to buy cars that i can re-sell very easily...

Thanks for your comments so far! I might take it out for a test drive this week...


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## Dowdy (21 September 2009)

I own a hyundai i30 diesel. Best car i've owned

 Diesel is cheaper then petrol and should always be since it's cheaper to refine.

 Diesel are great for overtaking since they have more torque

 Diesel engines are better - last longer, less wear. Just look at the old 1980's Mercedes

 Great towing capacity due to the torque


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## Stan 101 (21 September 2009)

Dowdy said:


> Diesel are great for overtaking since they have more torque




Large torque alone does not make a fast accelerating machine. Depends on where that torque is in the rev range and what that rev range is. Torque can be compensated for with gearing to give the illusion of acceleration, but it's not..


cheers,


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## Smurf1976 (21 September 2009)

I've driven otherwise almost identical vehicles in petrol and diesel versions. This wasn't a test drive but regular use at work, so I've done a few k's.

Bottom line is that unless you do actually want a race car, forget petrol. You'll need about 30 - 40% more petrol to go the same distance, petrol engines are inherently less reliable than diesel and there's really no performance issue with modern diesels (assuming there's a turbo).

In terms of performance, a couple of examples from real world driving.

Standing start at bottom of steep hill. 4 litre petrol engine - floored it all the way and it just manages to reach the speed limit (50) by the top. 3 litre diesel - reaches 50 half way up and could easily break the speed limit. Vehicle was a utility with identical tray and very similar load on both occasions.

1.9 litre diesel auto - no problem accelerating 100 to 110 up hills on the highway with 3 passengers and luggage. Comparable petrol vehicles would manage to do it but not as easily.

So I'm a convert. Never driven a diesel until about 3 years ago but would be reluctant to buy anything else now. Better economy, around 30% less CO2 (I'm not a green, but why pollute if you don't have to?) and decent on-road  performance with the modern ones.

Petrol? Well it's still the best fuel if you want outright acceleration. Or if you want to run a lawnmower. Diesel's a better option for just about anything else in my opinion.

Serious engines - trains, power stations, ships, submarines and so on are rarely (never?) petrol and there's good reasons for that. Too unreliable and too expensive to even consider it.

I've never driven an LPG car so can't comment on that. In theory though you'll use significantly more of it than with petrol (and somewhere around twice as much as with diesel) so there's not really that much running cost saving unless you live somewhere with cheap LPG.


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## awg (21 September 2009)

Aussiest said:


> My dad *swears *by those things.
> 
> Awg, i'm not a hoon. Just your normal average driver. Do you still think i would have trouble over-taking?
> 
> ...





The overtaking problem only comes about if you select vehicle that is either underpowered, (or low rev limit, which is less likely with the modern diesel engines)  

My answer was more of a technical observation, that is that petrol engines have more Power, but usually comparable max torque, for the same displacement.

this is due to the lower rev limit of diesels.

diesels have a better torque curve at low revs, which males them nicer to drive in most conditions, ie low rev city driving.

If you select a powerful enough diesel, in a light enough car, as others have mentioned, you will have no driveability probs at all.

my main experience with diesels is in heavy older vehicles such as trucks and Toyota Hilux, these vehicles have low redline, and not good for overtaking.
Torque and power fall alarmingly at high revs, unlike a petrol

new cars mainly have these issues ironed out, as far as I know.

I would stand by my comment that under no circumstance would i prefer to overtake in a diesel engine of the same capacity as a petrol.

resale should not be a huge issue imo

big + for diesel is fuel efficiency, but if that is your main consideration, LPG is cheaper.

very good diesel engines are very expensive to purchase


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## Macquack (21 September 2009)

How is the noise output of the new diesel engines? 

I have a Daihatsu diesel truck and it sounds like a bag of bolts. I gather the noise comes from the higher compression ratio compared to a petrol engine.


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## waza1960 (21 September 2009)

Peugots have had problems with fuel contamination in Australia .For a start our fuel is not the same quality as Europe.Late model diesel car engines' fuel systems run very high pressures and close tolerances making ultra clean fuel essential.Was a story of a Peugot broken down out west ,had to have the injector pump replaced cost $16k just for the pump.


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## marklar (21 September 2009)

Macquack said:


> How is the noise output of the new diesel engines?



The vee dubs still sound like a bucket of bolts, but at a lower volume than some of the older generations of oilers.  If they can make a diesel Eos and people actually buy it, they can't be too bad.

m.


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## awg (21 September 2009)

Macquack said:


> How is the noise output of the new diesel engines?
> 
> I have a Daihatsu diesel truck and it sounds like a bag of bolts. I gather the noise comes from the higher compression ratio compared to a petrol engine.




You pay for what you get, the cheap ones are noisy, the expensive ones are generally quieter, all other things being equal



waza1960 said:


> Peugots have had problems with fuel contamination in Australia .For a start our fuel is not the same quality as Europe.Late model diesel car engines' fuel systems run very high pressures and close tolerances making ultra clean fuel essential.Was a story of a Peugot broken down out west ,had to have the injector pump replaced cost $16k just for the pump.




the diesel injector pumps on the high quality sequential injector systems run at extreme pressure.

they are lubricated by the diesel.

if the fuel is contaminated by water, they are destroyed in seconds.

this is not an uncommon problem, as water infiltrates the service station tanks under various situations, and can also get into the car fuel tank


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## Happy (22 September 2009)

awg said:


> ...
> if the *fuel is contaminated by water*, they are destroyed in seconds.
> 
> this is not an uncommon problem, as water infiltrates the service station tanks under various situations, *and can also get into the car fuel tank*





Petrol car can get rid of small amount of water contaminated fuel by adding 100 ml of methylated spirit couple of times a year. But this is hit and miss, as you don't know how much water is there.


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## awg (22 September 2009)

Happy said:


> Petrol car can get rid of small amount of water contaminated fuel by adding 100 ml of methylated spirit couple of times a year. But this is hit and miss, as you don't know how much water is there.




this method works well with petrol, however, is not so much of a problem, as the fuel pumps are low pressure, so usually not harmed, also cheap to replace.

wont work with diesel, the HP fuel injector pumps are lubrication critical, and any contaminant will wreck them, cost thousands to rebuild.

I have repaired a few fuel tanks, you would be amazed how much water and rust is in them, cause fuel floats on water, it builds up at the bottom of the tank, and rusts them, water ingress mainly due to condensation


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## Dowdy (22 September 2009)

Macquack said:


> How is the noise output of the new diesel engines?
> 
> I have a Daihatsu diesel truck and it sounds like a bag of bolts. I gather the noise comes from the higher compression ratio compared to a petrol engine.




my engine on my i30 is louder then a cars petrol but it's only noticeable when it's idle


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## ajjack (22 September 2009)

For ordinary city use, best to stay with petrol.
There are not many small dedicated LPG  autos available
off the showroom floor.  
Diesel?  There are some small models avail in the sub 2 liter 
size, but they are not cheap.
By the time you factor in the price of diesel fuel and the
prime cost, there is no real saving over comparable petrol models.

Until there is a break thru with hybrids and elec vehicles,
petrol is still the best choice.


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## matty2.0 (22 September 2009)

if you're concerned about economy, why not get a hybrid vehicle? there are even electric vehicles for the saavy. 

btw ... i thought gav was the "aussiest"


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## Tysonboss1 (23 September 2009)

Smurf1976 said:


> I've never driven an LPG car so can't comment on that. In theory though you'll use significantly more of it than with petrol (and somewhere around twice as much as with diesel) so there's not really that much running cost saving unless you live somewhere with cheap LPG.




By my calculations you would use about 50% more litres of lpg when compared to diesel, So if I increase the price of LPG 50% from 50c to 75c, It's still a massive saving over diesel.

There is a reason why TAXIS run on LPG and not petrol or diesel.

If cost savings is what you want, you can't go past an LPG. When run on LPG my car has similar running costs to a PRIUS.


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## gav (23 September 2009)

matty2.0 said:


> if you're concerned about economy, why not get a hybrid vehicle? there are even electric vehicles for the saavy.
> 
> btw ... i thought gav was the "aussiest"




Haha wrong forum mate


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## gav (23 September 2009)

It all comes down to you, and what you want in a car.

- Does it matter if the car is rear or front wheel drive, or AWD?
- What type of driving will you be doing?
- How fun is the car to drive?  Is performance important to you?
- Does the interior meet your requirements/standards (comfort and looks)?
- Are exterior looks important to you?
- How important is fuel consumption?
- Do your prefer a specific brand or company?
- How important is re-sale value?
- Do you have any specific considerations? (room for kids, golf clubs, will your partner drive the car too, etc)
- And of course, how much can you afford?

For me, there is only one car that ticks all the boxes.  I can't afford it yet, but I know the wait will make me enjoy it even more...


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## awg (23 September 2009)

Tysonboss1 said:


> By my calculations you would use about 50% more litres of lpg when compared to diesel, So if I increase the price of LPG 50% from 50c to 75c, It's still a massive saving over diesel.
> 
> There is a reason why TAXIS run on LPG and not petrol or diesel.
> 
> If cost savings is what you want, you can't go past an LPG. When run on LPG my car has similar running costs to a PRIUS.





LPG is the cleanest fuel.

some things to watch out for.

two different styles of converter

sequential injection is the most modern, efficient and expensive, not all cars can be fitted with it though

older style converters are less efficient, but cheaper to fit

duel fuel conversions, while handy, are the least efficient.

takes ages to fill yr tank with LPG.

I have a notion that LPG, is going to have the excise increased soon

Dedicated LPG is good if you need a big car such as Falcon or Commodore, and do a lot of kms.

I suggest persons do calculations based on how many kms they do, mpg, and time they keep the car, plug in these, and you can work out what is the most economical car for you.

Hybrids are very expensive to purchase, and to my mind, maintenance and resale issues unknown, but questionable


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## Smurf1976 (23 September 2009)

Tysonboss1 said:


> By my calculations you would use about 50% more litres of lpg when compared to diesel, So if I increase the price of LPG 50% from 50c to 75c, It's still a massive saving over diesel.



OK, let's take the "base" car, petrol powered, as using 10 litres / 100km for an example.

A diesel version of the same car should use around 7 litres / 100km.

LPG conversion of the petrol engine would use around 14 litres / 100km.

You'll need twice as much LPG as diesel to travel the same distance. 

Locally, diesel is 128.9 and LPG is about 67.9 cents per litre. Add in the coming 12.5 cents excise plus GST on that, and LPG increases to roughly 81.65 cents per litre, about 27% more expensive than the volume of diesel required to travel the same distance.

If you have a dedicated LPG engine (which has significantly higher compression than a petrol engine) then you get the best of both worlds. A cheap fuel used with efficiency approaching that of a diesel engine. 

Given that LPG is now widely available, it would make some sense to produce dedicated LPG vehicles in my opinion. I assume marketing and consumer acceptance is the reason they're not common.


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## Tysonboss1 (23 September 2009)

Smurf1976 said:


> OK, let's take the "base" car, petrol powered, as using 10 litres / 100km for an example.
> 
> A diesel version of the same car should use around 7 litres / 100km.
> 
> ...


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## Mr J (23 September 2009)

awg said:


> I cannot agree, how are revs irrelevant if you want to overtake, in a manual car, commencing yr OT manouver at about 3500rpm and finishing at (say)5700rpm, without changing gear?
> 
> try that in a diesel
> 
> (most diesels redline below 5000rpm vs petrol 6000rpm, and their power and torque curve falls away at high rpm, although they are better at low rpm)




It's irrelevant because revs don't decide how well a car overtakes. What matters is an engine's powerband, and yes the characteristics between diesel and petrol engine's differ, but it is far more complicated than comparing revs. There are some very fast diesels, including race cars.


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## Kash Kosmo (23 September 2009)

I am a retired mechanical engineer by trade & I hold a Motor Mechanics Licence 
For Australian conditions Petrol is best followed by Gas or a combo of both 

Just to clarify diesel is a fuel oil and is currently more expensive than Petrol in Australia 
If not processed and stored properly it can cause problems more so in the more advanced European engines over Japanese engines

When they say in advertisements a diesel car can run 1000 KM on a tank please check the size of that tank & then judge the fuel economy 

European cars loose so much value its a travesty 
Take it from me I have owned a Lotus, BMW, Merc, Alfa, Citroen and while they were fun to drive they were worth nothing when it came to sell 

I now drive Toyota's & Honda's  and use E10 fuel 

KK


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## matty2.0 (24 September 2009)

gav said:


> Haha wrong forum mate




haha ... was wondering if you noticed or would reply!

OP is 'aussiest' i guess.


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## awg (24 September 2009)

Mr J said:


> It's irrelevant because revs don't decide how well a car overtakes. What matters is an engine's powerband, and yes the characteristics between diesel and petrol engine's differ, but it is far more complicated than comparing revs. There are some very fast diesels, including race cars.




In agreement on most all you say

however I maintain that in the majority of engines, the average torque to power band is spread over wider revs on a petrol than diesel.

ie can maintain useable torque for longer in OT without gear change

ie useable torque diesel 1000rpm to 4000 rpm

petrol 1800 to 5500  

not much I know, but still appreciable in OT situation

exceptions for specially developed diesels such as Audi

maybe I am spoiled as I have a V12 Jag, and used to drive an International 345cu 4wd...these motors have massive torque..the Jag has an almost flat torque curve from 1400 to 6000 rpm.

Could be to do with the way I overtake, always try and be near peak torque range at the critical moment


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## ajjack (24 September 2009)

Well said KK and I agree xcept for the E10.

Not only is LPG less economical, but also it produces  less power.
Power losses are not so obvious in a large 4 litre  motor,
but try LPG in a small 1.6, and its a different story.
Also not all motors are compatible to gas conversion.

Diesels are expensive to buy, and the ADO fuel is also exp.
as compared to petrol, with no regular price discounting.
If you drive less than 15K annually, then the economics of owning
a diesel are not there.


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## stocksontheblock (24 September 2009)

Doesn't add a single thing, yet when has that ever stopped anyone 

I would be more concerned about buy a Peugeot


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## Mr J (24 September 2009)

awg said:


> however I maintain that in the majority of engines, the average torque to power band is spread over wider revs on a petrol than diesel.




Fair enough. I don't have experience with the majority of engines available, so I could only compare specific engines. I prefer revs myself though. Otherwise it's like a lion without the roar .


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