Petrol vs Diesel

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Post by P616VKX »

4,000 RPM in my car is about 85MPH... And I don't know how people are saying sitting at 4,000RPM makes for a tiring drive? At 85MPH, the engine noise is so muffled by wind noise and the like, it's almost inaudible. And, the positive side of that is, at 4,000rpm, something magical happens (Not sure what) and the car seems to gain a burst of power at anything but very light throttle. (Not sure if the 1800-16 has VVTi or something, but it shifts!)

Diesels are out of puff by 3,500rpm at most, which is a shame as there's so much more to be used if it could be harvested... But due to the problems with my 90HDi Picasso, I'll say that the 1.8 Petrol Unit in the Xantia is much better on performance, servicing costs and usability. (Plus, the HDi was ever such a cold engine, the short drive to work would be freezing in the winter!)

Another positive on Petrol over Diesel... All the diesel-heads are buying everything that'll run on chip-fat at the moment, so petrol engined cars are very very affordable when adding in servicing requirements and so on!
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Post by Chlorate »

They're out of puff by 3500rpm but are usually putting out far more torque than a similarly sized petrol engine at much less revs than that, and that's the point, you don't need to rev some diesels as hard to get up to speed.


I don't understand the whole "diesels cost more to service than petrols" argument.
Engine oil and filters cost the same, fuel filters cost the same, air filters cost the same, glow plugs have to be replaced at a much longer interval than spark plugs and cost about the same...

If you're going to be running on WVO, yes you do have to change your fuel filter more often, but that's what an extra £3 every few months when you'll save that and more in a day just by filling up with fuel at half the price?!
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Post by P616VKX »

Chlorate wrote:
I don't understand the whole "diesels cost more to service than petrols" argument.
Diesel servcing intervals - 4-6,000 Miles
Petrol - 12,000 miles.

Double the cost per year.

Then theres the risk of the engine running away and revving itself into orbit until it snaps.
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Post by Chris570 »

P616VKX wrote:
Chlorate wrote:
I don't understand the whole "diesels cost more to service than petrols" argument.
Diesel servcing intervals - 4-6,000 Miles
Petrol - 12,000 miles.

Double the cost per year.

Then theres the risk of the engine running away and revving itself into orbit until it snaps.
It's not fair to compare an older style diesel against a newer petrol really.

Xantia V6 service interval 12,500 miles
Xantia HDi Service interval 12,500 miles.

and as for run on, you might as mention pinking and holey pistons.....

me? i prefer diesel for everyday car as it is a lot cheaper to run than the equiv petrol and is a nicer engine than a 2.0. (i won't compare against the V6 as that's not fair, although i'm sure the HDi is the winner below 4000rpm between the 2)
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Post by Citroenmad »

P616VKX wrote:4,000 RPM in my car is about 85MPH... And I don't know how people are saying sitting at 4,000RPM makes for a tiring drive? At 85MPH, the engine noise is so muffled by wind noise and the like, it's almost inaudible. And, the positive side of that is, at 4,000rpm, something magical happens (Not sure what) and the car seems to gain a burst of power at anything but very light throttle. (Not sure if the 1800-16 has VVTi or something, but it shifts!)

Diesels are out of puff by 3,500rpm at most, which is a shame as there's so much more to be used if it could be harvested... But due to the problems with my 90HDi Picasso, I'll say that the 1.8 Petrol Unit in the Xantia is much better on performance, servicing costs and usability. (Plus, the HDi was ever such a cold engine, the short drive to work would be freezing in the winter!)

Another positive on Petrol over Diesel... All the diesel-heads are buying everything that'll run on chip-fat at the moment, so petrol engined cars are very very affordable when adding in servicing requirements and so on!
4000rpm is a lot of revs for a car to cruise at though I was meaning at 70. Your 1.8 is higher geared than the cars I mentioned. My C5 HDI is extremely quiet at 70 and no real noticeable difference at 85 and beyond, certainly no engine noise at 70, wind noise is negligible and tyre noise very subdued. It took me some getting used to at first as if not using the cruise or keep an eye on speed, you can soon be doing very high speeds without knowing about it.

One reason petrols sit at higher revs at high speeds is just because of that. If you had one which could do 2000rpm at 70mph the car would actually not maintain its speed as there is no low down torque nor power to keep up the drag and gearing of the high speed. Hence why a 1.6 sits closer to 4000rpm which is where its power starts to arrive. A HDi sits in its power band at motorway speeds and so provides similar and more pull than your petrol.

For this reason a diesel makes for a more refined car to drive faster. I like going out every now and again and having a good drive and using the revs in a petrol. But for daily use, especially with passengers, to make good progress as I always do requires many revs to be used and the appearance of thrashing it might be apparent to passengers. In the strong diesel its just as quick but you need to work the revs far less, giving a more comfortable performance. Plus there is usually always power when you need it, without having to stir the box and make the revs rise, its just off.

Of course a smaller petrol engine is not going to be comparable with a big V6 or V8 which do have low down torque and cruise at less revs as a result. Likewise the size and type of diesels differ vastly and this is therefore a generalisation.

As for the fact there is no pull after 3000rpm, it depends on the diesel. I find the 138 HDis pull well up to 4000rpm, they do actually rev to 5000rpm but the power levels - not drops. There is no point in reving past 4000 or even 3500 as the power is so low down, aside form what you say the top range is not wasted in a diesel, its simply not needed.

However I know most of the fairly recent 1.6i petrols in the Citroen Peugeot range seem to do nearing 4000rpm at motorway speeds and it is annoying to have a engine buzzing away in the background. Noise is tiring and it is wearing on you over a long distance. Long distances should be done in comfort, quietness and refinement in my opinion.

A 2.0 16v XM does 3000 at 70mph, as does my Activa, they are not noisey cars as thats not badly geared for a petrol car. I do find the Xantia engine can be heard at 70 and the XM less so, but that would fit in with its executive status. Though I guess your 1.8 Xantia to be similarily geared so not comparing to my 4000rpm at 70 issue.

Our 1007 Peugeot was 4000rpm at 70, the engine noise was intrusive and tiring on a long run, in fact it stopped my taking it on long runs after the first. Mind, the C5 HDis do tend to spoil you for refinement, as does the 2.1 XM.

As for servicing, your going back a long way to 4-6K mile service intervals, old design diesel engines. Most modern engines are 20K miles between services now and some even 30K miles. Personally I dont agree with the longer servicing so do every car, petrol or diesel, at 6000 mile intervals. My C5 included and that is stated to have 20K mile intervals.

I don't understand what your saying about the engine running away with itself, not with the correct oil level and not is looked after.

As for warming times, the HDI is very rapid at warming up in the winter in my opinion. For a diesel they take far less time than many others. Have you driven a TDi engine? I did 11 miles in my Seat TDi one winter morning before the temp needle even moved! The HDi is very efficient with its heat and ive not had a problem in the winter months.

Its not really the fact that people are buying diesels to run them on veg which keeps prices high, as only the XUDs and some other diesels run it. Modern deisels like the HDis, TDIs, TDCis, etc etc all should not be run on it due to their injection system. Diesels have always and will always be worth more than the equvalant petrol as people find them more desirable. Unless, as Luke has told me, its a 1.9DCi renault, which are often worth less than the petrol versions :lol:
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Post by Deanxm »

Im not going to go into the whole which is best thing but i drive all sorts, DCI's and other common rail dervs, ive owned a few XUD's and a lot of petrol's but im a petrol man.

Dervs dont rev so thank god they have some torque from 1500rpm or they would be about as usefull as a choccy tea pot, the derv is not quiet in comparison to a comparible Petrol engine, they just are not, you can always tell with the subdued clatter or rattle under load, however they do have one big advantage, economy.
when i was working on the mainland and was doing big mileage i had a derv and it was a nice drive, pulled well although like most dervs throttle response is slow and they do not like being thrashed to the red line too much, the DCI for instance and the idi in my old transit were especialy bad, you can stap the throttle into the floor and release quickly and nothing happens at all, the injection just cant keep up so you cant steer them on the throttle like a petrol either.

Petrol does not make sense over long trips, it just doesnt, but for the average person doing up to 10k a year you are wasting your time with a derv, the increased fuel cost, plus the extra purchase cost of the car means that you would be better off with a petrol BUT, and this is where the Diesel engine is awesome.............you can burn any old oil in it you like, reasonably cleanly :wink: ok it doesnt work in the newer engines but i would never spend my own cash on one for that reason

Petrols heat up quicker than dervs, no arguement there, the derv has to have a derv or electric heater imo especialy on short journeys, even my old dino petrols are blowing warm air in under 30seconds.

It all comes down to cost, the derv boys can argue the derv is the best car, easy drive etc, etc and with the coming of the common rail engine i agree massive leaps have been made but dont compare a 2.0 turbocharged derv to anything other than a 2.0 turbocharged petrol, if price was no object we would all drive V8's everywhere and only plant would be diesel and it would be running red.

Also the XUD is the best derv you can get!, maybe even today, yes its not as refined as a Common rail but they have their issues too, in my eyes the XUD was the peak of Derv design in some ways and the common rails are just bristling with the only thing any true derv lover didnt want, electrics, a good derv should be economical, give good power delivery and be indestructable, you cant fix a common rail with a hammer and pry bar:wink:

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Post by andmcit »

Yep, totally agree with all that Dean; my mileage is sufficiently low to
warrant silly big engined less economical to run petrols and I'm a happy
man because of it. I just cannot get economy out of a diesel as my driving
style is merciless and high revs/speed as that is the way I drive accustomed
as I am to the petrols. Over a long trip a decent petrol will be happier but
I'm never going to say it'd match a leisurely run in a HDi - some folk that
have a block of wood under their throttle apparently get 50-60mpg out
of their Xants.

Just don't get stuck in front of me as I'll be gnashing my teeth shouting
obscenities inside my car and itching to get past.

Apparently we're all doomed anyway so may as well go down with a smile
on the face rather than an Excel spreadsheet showing averaged out over
the year diesel mpg returns...
Last edited by andmcit on 14 May 2011, 15:43, edited 1 time in total.
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Post by Citroenmad »

Ok, so only 2.0 turbo diesel should be compared with a 2.0 turbo petrol.

My thoughts then, my 2.0HDi 138 vs my 2.0TCT ...

Giving a petrol engine a turbo does seem to give it diesel qualities, with low down torque and power without the need to rev it, it has power there. Something I like. However, the turbo petrol does that AND it revs very nicely and highly and its a joy to have that long and usable power band when making the most of the Activa. Its got more power and its lighter than the C5 I have, so its quicker. It sits at 3000rpm at 70mph and so its quite refined but has plenty of pull without having to change down, as the turbo is spooled ready. I did a 0-something or other :roll: from a set of traffic lights on a dual carrigeway the other day and it impressed me. As standard the 2.0TCT has the same torque as a 2.1TD XUD and only at very slightly higher revs, you dont have to go mad with it to make it move. With its 40bhp more than the 2.1TD it goes quite well.

The 2.0HDi 138, well that does have good performance and with a 0-60 of a shade under 10 seconds its not a slug. Lots of torque when its needed and pull low down. Its 6 speed box gives it high gearing and brings down the rpm to a little over 2000 when cruising at 70mph. Its a very refined car to drive and for that reason a better choice for a motorway blast due to its slightly quieter nature.

I can't decide which one I like best, the TCT is faster but it does have more power, revs nicely AND has low down pull like the HDi. The HDi is low reving at speed, its quieter at speed and its a very refined unit.

The above without the costs involved. Costs:
The TCT does 28 at best and around 25/6 on average, so roughly half that of the HDi 138 which does around 50 on average even with my spirited driving - though I do a fair few motorway miles which improves my economy. So it does make financial sense to drive the diesel for a daily car and have the petrol for the nice days and roads.

Im not an economical driver though, I hate going slowly and try my best to get past the slowies which you encounter on every journey! So doing high motorway speeds in the diesel makes much much more sense both financially and otherwise.

Diesels may cost more to buy, but dont forget that makes them more valuable when you come to sell on and also easier to sell too. I have no problem selling HDI C5s, I wish I had one to sell every day of the week!
andmcit wrote: Apparently we're all doomed anyway so may as well go down with a smile
on the face rather than an Excel spreadsheet showing averaged out over
the year diesel mpg returns...
:lol: That is brilliant! :lol:
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Post by Xaccers »

Ok, how the hell do you get 25mpg from an Activa?
Doing 56mph for an entire tank only got me 20mpg!
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Post by Chris570 »

Xac wrote:Ok, how the hell do you get 25mpg from an Activa?
Doing 56mph for an entire tank only got me 20mpg!
Xac, you make me love the V6 even more :wink:
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Post by Citroenmad »

Xac wrote:Ok, how the hell do you get 25mpg from an Activa?
Doing 56mph for an entire tank only got me 20mpg!
:lol:

20MPG doesn't seem quite right!

Well in truth ive worked it out once and then just pour in the juice as and when, im not bothered about its economy as I don't use it every day.
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Post by Xaccers »

Chris570 wrote:
Xac wrote:Ok, how the hell do you get 25mpg from an Activa?
Doing 56mph for an entire tank only got me 20mpg!
Xac, you make me love the V6 even more :wink:
Why oh why didn't we get V6 Activas over here? It's so unfair!

Of course a bosch'd 2.1TD boosted to 150/200bhp Activa running on veg would do me perfectly.
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Post by Chris570 »

Xac wrote:
Chris570 wrote:
Xac wrote:Ok, how the hell do you get 25mpg from an Activa?
Doing 56mph for an entire tank only got me 20mpg!
Xac, you make me love the V6 even more :wink:
Why oh why didn't we get V6 Activas over here? It's so unfair!

Of course a bosch'd 2.1TD boosted to 150/200bhp Activa running on veg would do me perfectly.
If I had an activa I would certainly have 406 v6 engines in my ebay watch list.....

although a tuned veggie diesel has its perks :) I loved my 1.9TD on veggie
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Post by Citroenmad »

Xac wrote:

Of course a bosch'd 2.1TD boosted to 150/200bhp Activa running on veg would do me perfectly.
Hmm, nice daily 8-)
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Post by Xaccers »

Easier to do than a V6 conversion too.
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