[Closed] Diesel Vs Petrol

Mboy - how you been recently?

Moving onto the subject of Japanese petrol cars briefly, oddly enough, reliable as most of them are, fuel economy never seems to have been a strong point with Jap cars. You'll get much better economy from most European petrol models than you will from most of their Japanese equivalents.

I wonder if it's due to the Japs being taxed on displacement, rather than CO2 production. Therefore, they milk the 'most' out of their engines (and why a lot of jap hot hatches are 2000cc - pretty smart getting 450bhp out of a coke bottle!), which will result in more fuel being burnt for a given displacement?

DrP

a DMF, Clutch, EGR and Alternator all at ~40k. It's the first car we've had any of these bits on

I think you'll find most of your other cars will have had clutches and alternators 🙂

Our next cars will be [s]petrol[/s] not Fords

FTFY

not some forum warrior's boasts about how good a driver they are based upon their own ego and massaging of figures for their own purpose.

Can you just chill out? He's relating experiences plain and simple. You seem to think we're all having a go at you or something? I'm not reading aggression into any of these posts except yours, and possibly flow 🙂

Mboy - how you been recently?

OK cheers, other than being skint and needing to either spend a load of money on my Audi, or sell it and buy something cheaper!

I have always had VAG cars. When I sold the A3 TDI I thought I would look at other makes, problem was none of them drove as well, were as nice to be in etc.

Ended up buying the same car with a different engine, even the same colour 😆

The car is also 11 years old

The thing is you're not comparing like with like if you're looking at standard petrol cars getting almost as good fuel consumption as you do, when the equivalent diesel would be better than 50mpg.

aracer, I was comparing like for like in terms of power output for cars made around that time, rather than engine size. Most 2L diesels peaked at about 110bhp back then, to get the 150bhp a 2L petrol made you needed a bigger engine. Call me old fashioned, but I like to know if I want to put my foot down, I can actually overtake something pretty quickly! I've owned a few underpowered cars in the past, it's nice to have a bit in reserve.

You're right about the 4wd though, it's about a 15% effect according to the quoted figures for the fwd vs 4wd version of my car. Like I said though, I', not actually complaining about my MPG.

don simon - Member
What's the 2.7 like to live with boblo? A couple of Le Mans Avants have vaught my eye

It's pretty good though I'd go for an auto as the manual cen be a bit snatchy on pull away. Otherwise, car is smooth, economical and in normal guise, 180bhp so plenty powerful enough. For long term ownership, it has chain driven cams rather than the belt replacement job required on the 2.5L@ 80k (IIRC). That's an expensive job on the 2.5L.

I had mine chipped though and there's loads of grunt whilst returning the mpg's above. I didn't fancy the 3.0L for the extra power as it only came in 4x4 mode and for 99.9999% of my driving, 4x4 is irrelevant.

I'd buy another though auto.

When I bought my Leon fr I test drove the petrol and the diesel back to back. I've never driven diesel before and had strong preconceptions of how horrible it would be. I was pleasantly surprised though. Yes it was noisy from start up, but after 10 mins it was fine unless you really gunned it. There was gob loads of pull when you put your foot down but it was all very short lived before requiring a gear. The only other thing I disliked was the length of time it takes for the heaters to start kicking out some decent heat. Seemed to be the same in all the diesels I've since driven too, down to the engine warm up time? In the end I decided I would have either depending on which car I found secondhand with the spec I wanted to become available first. Petrol won

M6 - When was that? The all-then-nothing thing is a feature of a particular generation of VAG TDIs. I think Seat continued using them up until relatively recently, I think a 57 or 58 plate Altea I test drove had it. Later PD engines and common rail engines are not like that.

The heater thing is because more of the energy goes to powering the car, instead being wasted through the radiator 🙂 I read somewhere that when idling a petrol uses six times more fuel than a diesel. Maybe that's why my car has electric heaters fitted so I get warm (ish) air straight away.

I was reading about the new BMW 3 series (out next year) and BMW have put alot of work into their petrol engines this time around since they reckon that they will see a swing back to petrol purchasing over the car's 7yr life cycle. All due to the difficulty / cost of making diesels meet stricter future emissions criteria.

since they reckon that they will see a swing back to petrol purchasing

Yeah thanks to them and their swirl flaps!

It would be interesting.. more people buy petrol cars, demand for diesel drops, it gets cheaper.... VW might be annoyed with that since they've put so much effort into diesel. Toyota and Honda should be laughing with all their hybrid development. Petrol hybrid FTW.

Molgrips, yup 57 plate - pre common rail engine, couldn't stretch to the revised model

We had a Volvo XC90 diesel for 6yrs, traded it in for another last year, it just ticks all the boxes. Only do 6k a year, starting to think it isnt worth paying the extra for diesel. Flip side is we're a family of 5, couple of dogs, grandparents who visit, always ferrying other kids around.....7 seats is almost essential, dont know what else we could buy would do the job with a petrol engine.

I have a 175bhp diesel (Audi A6) and a 150bhp petrol (Mazda 3) - both manuals - so I think I have a couple of pretty comparable cars - the power to weight ratios must be pretty similar (although I have never checked).

The car I prefer to drive depends on the type of driving I am doing - for going up and down the motorway it is the diesel every time- it is just smooth and refined (although that may be more to do with the car itself, not the engine). But I still find the petrol engine to be far more responsive and (surprisingly) has more grunt at the lower end and is much more forgiving of bad gear choices - it just doesn't have the dead spots the diesel has. So when I am zipping around town or wanting to get a bit 'sporty' I much prefer the petrol unit.

I was getting 21/22MPG on a run but since the EGR blew coming back from France its only doing 18MPG. A new EGR and service is £900.

Why do EGR's keep failing....

Somethign else is probably wrong cookies. The EGR is just a valve. They get coked up if there's a lot of smoke. So something could be causing soot and smoke.. Possibly short trips, possibly something else.

... This is of course 35 ACTUAL mpg, not some forum warrior's boasts about how good a driver they are based upon their own ego and massaging of figures for their own purpose.

(real figures worked out from how much fuel I put in and how many miles I do, as I need to do it for expenses)
.
So you leave your @rsehole attitude for someone else and chill the **** out.

I think the low economy in this example is a factor of the car itself. the equivilent mondeo (st-tdci with 155bhp) has a combined rating of 46mpg. alternatively (for less money) you could probably just get a 130bhp one and chip it for the extra boost, which would give marginally more mpg (48 combined cycle). You'd probably also find that a 2wd car with 150bhp would be significantly more nippy than a 4wd 150bhp car, as its not got 15% additional drag that the 4wd entails (to compare it to the mondeo again (as its a good benchmark) - the 130bhp mondeo is as swift to 60 as the 155bhp audi despite the lack of traction)

Some petrols are now doing dmf to try to reduce the noise/vibration in the cabin, so the window for one without that tech is fairly narrow

there isn't a definitive 'cut off' for a diesel being 'worth having'. Diesels can have expensive repairs and cost more to buy - however they typically hold their value better, cost less to service (no spark plugs), cost less to tax (if a newer car) and use less fuel. There is a cutoff but you'd have to put a little spreadsheet together to figure out what is best. Independant warranty places (such as warrantydirect) don't charge different amounts for covering a diesel vs a petrol (in the example of the mondeo, £393 each way) so there can't be *that* much more in cost of repairs

OP
ive been wondering similar myself, as im thinking about changing my car next year, but the bottom line (for me) is this,
i have a 2l mondeo tdci, and the worst mpg i have had is 42 (booting it around town, air con on full blast)these are actual figures, my car doesnt have a trip computer.
my mate has a 2l petrol vectra (similar weight to the mondeo) and the BEST he has had is 45mpg, his average is 27(trip computer).
my average is around the 50mpg mark.
my car has done 144k with nothing other than routine service items/fair wear and tear ie brake discs etc.
i really dont know which way to swing next, probably a 2l petrol in slightly smaller car tbh.

I'm amazed at those Passat figures. I have 2.0TDi on 56 plate and only get 48 on a long run at 70mph. I've only ever seen 50 when its been heavy traffic and speed drops to 50-60 max. Its frustrating to hear 60+ figures from the same car. Its the first time I've bought VAG and right now I'm not convinced enough to stay with them next time. Have you chaps had injector swaps or any other issues? Do you run fuel additives like Millers or redex?

By the way my trip computer is very accurate. Can't say how much exactly but on the few times I've measured it over a tank its been close enough for me to believe the mpg display.

Silvermatt - cruise control?

Gradual creeping acceleration is your worst enemy, especially on motorways.

Oh, and buying scilica compound tyres (Nokian V in my case) added about 2mpg.

I don't use cruise control very often - typically only on long journeys and when its quiet. I generally drive on dual carriage ways when its busy so cc is a pain to use. Should using it make a significant increase in mpg? I've not noticed it make a difference to be honest.

Tyres are Kumho I've no idea what compound this is. I'd probably buy Falken next time just from my perceived value for money of this brand.

Well now I'm shitting it - just bought a 2006 Skoda Octavia Estate 1.9TDi... 😯

what about your driving on DCs makes it hard to use cruise? are you braking? are you booting it? are your tyres pumped up? do you have the windows shut and aircon off? are you driving shortish (<10 mile) journeys from cold?

prezet - Member
Well now I'm shitting it - just bought a 2006 Skoda Octavia Estate 1.9TDi...

Why are you "shitting it"?

I've got a Seat Ibiza with the same engine - 130bhp version. It's done 173k miles. Only engine related issue was an intercooler pipe coming off. Turned out to be the wrong clip used from new to hold it on. It lasted 7 years or so, before failing. Replacement pipe & clip - £45 fitted.
Only other thing that failed unexpectedly was a wheel bearing at 38k miles, oh and the air con compressor died last year that cost £500 fitted.
I can get 55mpg out of it without really trying & at the moment in my 'driving miss Daisy' mood, I am getting closer to 60mpg average. Best from a full tank so far is high 63mpg (genuine calculated, not trip computer).

Why are you "shitting it"?

All this talk on here is a bit scary about diesel bits failing.

prezet - Member

All this talk on here is a bit scary about diesel bits failing.

I wouldn't worry too much about it. So long as you have it regularly serviced, use the correct spec oil, don't rag it from cold etc. it'll (probably) be fine.

I disagree. DMF, DPF and so on have no relation to whether a car is

a) serviced
b) ragged from cold
c) correct spec oil

A silver lining, looks like the Octavia won't have a DPF:

[url= http://www.pistonheads.com/gassing/topic.asp?h=0&f=86&t=884383&mid=0 ]http://www.pistonheads.com/gassing/topic.asp?h=0&f=86&t=884383&mid=0[/url]

😛

No booting it or braking just trudling along with the flow. Its always busy bumper to bumper at 70 ish but it ebbs and flows which is why I don't use cc. I'll give it a go for the next few days and see if I notice a difference.

Tyres pumped up and checked regularly (they hardly lose any pressure over a month or more). Windows shut but aircon is generally on. I don't tend to use the econ setting ever. Journey is 20 mile drive each way icluding quarter mile at each end on urban roads. In my mind it should be an decent commute for fuel efficiency.

I'm sorry you don't like my MpG figures (or yours)..... but that's what I get, why that would wind you up so much, and cause you to start throwing insults about is a mystery.

Have you read a word I've written?

I didn't start this thread to have an mpg war. I'm not unhappy with my economy figure from my car, I chose that car for a reason. I'm actually (I'll say it once again for those not paying attention) exceeding the manufacturers stated combined cycle figures, the first car I've had in ages that does.

My issue is with all the hidden costs that go with owning a diesel. With newer ones you've got the DPF's and DMF's and EGR's that can fail, with an older car like mine it's the diesel pump, the turbo and in my case the cams you've got to worry about wearing out.

I think the low economy in this example is a factor of the car itself. the equivilent mondeo (st-tdci with 155bhp) has a combined rating of 46mpg. alternatively (for less money) you could probably just get a 130bhp one and chip it for the extra boost, which would give marginally more mpg (48 combined cycle). You'd probably also find that a 2wd car with 150bhp would be significantly more nippy than a 4wd 150bhp car, as its not got 15% additional drag that the 4wd entails (to compare it to the mondeo again (as its a good benchmark) - the 130bhp mondeo is as swift to 60 as the 155bhp audi despite the lack of traction)

In fairness you're talking about newer cars, with newer engine designs. My 2.5L V6 was around since about 1994, the cars you mention above have much more recent engine designs which will account for why they're more efficient (as well as only being fwd) and can produce more power per litre.

Aircon hardly makes any difference these days.

Well now I'm shitting it - just bought a 2006 Skoda Octavia Estate 1.9TDi...

You've no need to as you've bought a car with a late 90's diesel engine. Rough, but less to go wrong.

No booting it or braking just trudling along with the flow. Its always busy bumper to bumper at 70 ish but it ebbs and flows which is why I don't use cc. I'll give it a go for the next few days and see if I notice a difference.

Tyres pumped up and checked regularly (they hardly lose any pressure over a month or more). Windows shut but aircon is generally on. I don't tend to use the econ setting ever. Journey is 20 mile drive each way icluding quarter mile at each end on urban roads. In my mind it should be an decent commute for fuel efficiency.

it could be your journey style. I can't measure your aircon cost, but lets say it uses 500ml of fuel per hour. that'd be about 4mpg lost

for your jouney, you car is probably only running at its most efficient for 10 miles each way (50% of your travel). My personal car usage often involves journeys over 100 miles, probably average 50 miles. If I had the same car, it'd be at its most efficient for 80% of the time. if the car runs at 35mpg when cold but 60mpg when hot, this could be your difference

In fairness you're talking about newer cars, with newer engine designs. My 2.5L V6 was around since about 1994, the cars you mention above have much more recent engine designs which will account for why they're more efficient (as well as only being fwd) and can produce more power per litre.

completely agree, but in the same light, I don't think its fair to compare that car to a modern petrol either. in the 90s you needed a similar engine to give you that power in petrol - the volvo 850 (non turbo) got about 160bhp from a 2.4l engine, and averaged ~25-30mpg.

5lab - Member
I disagree. DMF, DPF and so on have no relation to whether a car is

a) serviced
b) ragged from cold
c) correct spec oil

as above, no dpf in an '06 Octavia 1.9 TDi.

Servicing can identify wear etc. early that may prevent catastrophic failure of parts.
I have been told that PD engines are quite sensitive to the correct oil being used, hence my comment about correct spec oil. Do you not agree that correct spec oil & frequent changes will help prolong the life of an engine?

What are the "and so on" bits that you refer to?

Anyhoo - I have mine serviced regularly, make sure the garage use the correct oil & don't rag it from cold. It's lasted 173k miles with no diesel engine specific parts failing apart from a £50 hose mentioned above (that any car with a turbo will also have)......it'll probably fall to bits on the way home, now I have typed this...

now its £1100 for an EGR. Mine's elctrical and so shonky that Fiat make you buy a wiring loom to go with it, with the possibility of a remap....

^^^ oof!

I thought £500 for a new air con compressor was a lot to fork out!

Servicing can identify wear etc. early that may prevent catastrophic failure of parts.
I have been told that PD engines are quite sensitive to the correct oil being used, hence my comment about correct spec oil. Do you not agree that correct spec oil & frequent changes will help prolong the life of an engine?

What are the "and so on" bits that you refer to?

don't get me wrong, servicing is a great idea, as is using the correct spec of oil, however lots of people have problems with modern diesels which servicing wouldn't fix, such as

Clutch
DMF
DPF
Injectors
Turbo seals (the bearings will last longer with regular servicing but not the seals)
anything related to a sensor going wrong
some muppet putting petrol instead of diesel in

The only thing regular oil changes do really help with (other than the turbo bearings mentioned above) is bore wear on the engine. This is still an issue on higher milage (150k+) cars, but for most cars other stuff causes the death of the car prior to this becoming a factor..

completely agree, but in the same light, I don't think its fair to compare that car to a modern petrol either. in the 90s you needed a similar engine to give you that power in petrol - the volvo 850 (non turbo) got about 160bhp from a 2.4l engine, and averaged ~25-30mpg.

Volvo's have always been lazy, torquey engines. Most other manfucturers 2 litre 16 valve engines were pushing out roughly 150bhp since about 1994. My old 1998 Pug 306 GTi-6 had 167bhp! So I'm gonna stand by my original comparison.

but if you're cherry picking like that, the very engine you have put out 180hp in some states of tune (72bhp/litre) which isn't that far off what most diesels do today. Hell VW had a mk5 golf with *half* that much power

use a quality de coke agent 1-2 times a year(forte recommended by MOT stations), will help stop egr coking + use decent fuel cheap ones have very little detergent in.

A lot of modern diesels suffer from intake manifold failure, or more specifically, the swirl flaps get bunged up and fail.

All this euro 4 shizzle has resulted in the inert exhaust gas, which is rich in carbon, being recirculated through the EGR and intake manifold to reduce the combustion temerature and thus the amount of nitrogen oxide. This is all good, but not when the manifolds also full of oil vapour from the heavy breathing they do. Flour and eggs / oil and carbon, same effect.

Regardless of driving technique, they can, and more often will eventually bung up. If its not the EGR that fails, its the manifold swirl flaps that just cant open any more for the wall of crud behind them. Depending on the car, its then a new intake manifold as they snap the plastic link arms that connect the flaps. Either way, it can be a very costly repair, and its very very common.

Im sticking with petrol for now. You can pick them up a lot cheaper than diesels and they're just less risky if your on the second hand market.

If I was buying new, and with a waranty, then shifting it on after 3 years, then a diesel may make more sense.

Regardless of driving technique, they can, and more often will eventually bung up.

I took mine off my 1.9 TD to clean it, convinced it'd be clogged. After 180k miles there was a flim of soot on the inside. I was surprised.

Anyone know why a simple valve being blocked would result in a £1100 repair bill?

I was getting 21/22MPG on a run but since the EGR blew coming back from France its only doing 18MPG. A new EGR and service is £900.

Why do EGR's keep failing....

dunno, but ive had two go, one on 2.0L petrol A3 (300quid thank you very much) one on a 1.6D Volvo C30 (free under warranty) both cars went at just under 3yrs old as well.