Car running costs - mid-size car - diesel vs petrol.

[DanceswithUnix]

That very much depends on the diesel (and indeed, petrol) engine in question. While many diesels feel terrible, there are several more free-revving examples that feel more like driving large capacity petrol engines. And conversely, modern small highly turbo'd petrol engines can feel quite like diesels

I had the Alfa 1.9 multijet which is supposed to be one of the best to drive diesel engines out there, and I didn't really like it

As you say modern petrol engines are going the same way, but even the utterly tricked out 170bhp 1.4l petrol engine I have now is more fun than the diesel.

[OilSheikh]

I have a 2008 Ford Focus Ghia 2.0L automatic

Road tax £300 /year
MOT £40 / year
Petrol cost erm.. petrol prices vary and depends upon how much you drive. £40 covers to and from London to Nottingham for example
Insurance £400 / year

and pray to God no major issues develop throughout the year!

[peterb]

With the current move against Diesel engines, the difference in fuel price isn’t going to reduce anytime soon. The only real thing in favour of buying a second hand diesel now is that at some point in the future you may benefit from a scrappage scheme,

Personally I drive a larger Diesel engines car (3litre straight 6) and it drives like a dream even with 115K on the clock. But given the age of the car, it’s worth next to nothing second hand so I’ll run it until something major fails and then seriously think about an EV.

Diesels are possibly slightly cheaper to service, and if most of your travelling is on a motorway at a constant speed (cruise control) diesel will give you better economy. (At the moment my local motorway network has a mandatory 50mph limit - which has made a very significant difference to my mpg figures!)

[Butcher]

Consider aerodynamics for motorway efficiency as well. A saloon car will give much better economy than a similarly sized SUV just because it has much better aero (largely because the SUV is so much taller). At 70 mph aero drag is the main energy loss.

On a motorway cruise my car is significantly better on fuel than the previous one, despite being NA instead of turbo (which should be great at low load). I think a lot of that is because it has about 25% lower drag.

[Macman]

Take diesel any day of the week

The range I can get on my C250d is pretty sickening. Drove to Manchester and back, on both legs I was getting 60+ mpg. And on other days, I plant the foot and it just leaves.

I'm wanting to chip it but the gf isn't having it lol.

[Ttaskmaster]

What mileage does it give on motorways?

60mpg is ridiculously easy with these things.
I get about 70 average, according to my various measures, but you can get much more if you really pay attention to how you drive. PD engines were generally more efficient than CR. However, a lot depends on how often you get caught up in traffic.

I thought the PD engines ran at a higher compression ratio, making them more prone to small particulates and NOx emissions? So a PD engine would benefit in emissions from a DPF, they just weren't mandated back then so weren't fitted.

Nope.
DPFs, as required by Euro5, actually killed off PDs as DPFs were mandated.
"To activate self regeneration, a very late cycle of injection needs to be added; the fuel is injected post combustion which increases exhaust temperature which starts the regeneration process. As the timing of this injection is controlled by a mechanical factor, i.e the camshaft, there is only so much that can be done. The PD engines fitted with the DPF have a different camshaft with an additional profile to the lobe; this gives another fuel injection post combustion for regeneration. However this all has to happen within 360 degrees of camshaft rotation. For there to be time for the injector to work again for the next cycle, this obviously has some serious limitations".

Basically, what you gained in greener exhausts you lost in lower fuel efficiency and less reliable fuel pumps. More so once cars started to age and, since people never looked after them, fail. Many diesel drivers never got the car hot enough to initiate the self-regeneration anyway, especially with the ever-increasing traffic loads, so DPFs were often pointless.

Particulates isn't about soot, it's the really microscopic particles that get deep into your lungs, hence direct injection petrol engines now have to be fitted with them.

DPFs just catch particulates and break them down smaller so they aren't all detected by test equipment, really!

[kalniel]

DPFs just catch particulates and break them down smaller so they aren't all detected by test equipment, really!

Ideally oxidising them well so they get expelled by our breath rather than lodging... but yes, I've heard the argument that actually you want thick black sooty fumes because then at least the carbon lumps are big enough to drop down to the ground rather then being breathed in..

[Zak33]

worth knowing that not all diesels have DPF.

they were on large cars higher power jobs to begin with

My 1.9 Octavia 130 04 (last of that shape) doesn't have one

but at 10k per year.. I'd but a Japanese petrol car. Not a diesel.

[Ttaskmaster]

worth knowing that not all diesels have DPF.
My 1.9 Octavia 130 04 (last of that shape) doesn't have one

We already covered all that, mate... including bigging up the Octy!

but at 10k per year.. I'd but a Japanese petrol car. Not a diesel.

Reason?

And since we're here:
https://www.youtube.com/watch?v=Wk-isKUjWBQ

[DanceswithUnix]

Nope.
DPFs, as required by Euro5, actually killed off PDs as DPFs were mandated.
"To activate self regeneration, a very late cycle of injection needs to be added; the fuel is injected post combustion which increases exhaust temperature which starts the regeneration process. As the timing of this injection is controlled by a mechanical factor, i.e the camshaft, there is only so much that can be done. The PD engines fitted with the DPF have a different camshaft with an additional profile to the lobe; this gives another fuel injection post combustion for regeneration. However this all has to happen within 360 degrees of camshaft rotation. For there to be time for the injector to work again for the next cycle, this obviously has some serious limitations".

Basically, what you gained in greener exhausts you lost in lower fuel efficiency and less reliable fuel pumps. More so once cars started to age and, since people never looked after them, fail. Many diesel drivers never got the car hot enough to initiate the self-regeneration anyway, especially with the ever-increasing traffic loads, so DPFs were often pointless.


DPFs just catch particulates and break them down smaller so they aren't all detected by test equipment, really!

So from your description, some PD engines *did* have DPFs which just required a funky camshaft arrangement. And if some people don't do long journeys and hence clog up their DPF, that just shows that the DPF was doing a super job trapping particulates else it wouldn't have filled up. That doesn't make the DPF pointless, it just makes it annoying for those people that chose the wrong sort of car.

All of the output can be measured, and it is from huge soot particles down to the CO gas. The fine particulates and NOx are the worst though, so it seems sensible to minimise those even thought DPFs and cat converters always hurt fuel ecomony (that really isn't a PD thing). What killed PD is that CR engines give better economy figures and sound less like a tractor. The fact they fall apart at 150K doesn't matter much to people looking in the showroom at a new car.

Edit: Just looked at what the video was you linked. The thing is, the experts (who clearly see *lots* of these engines) couldn't believe how good the engine looked, which says to me that they see a lot of low mileage engines that are completely coked up and shot and what you see in the video isn't typical. By the end of the series hardly any of the original car was left, it should have been called "We built a car from scratch around an old death trap".

[Ttaskmaster]

So from your description, some PD engines *did* have DPFs which just required a funky camshaft arrangement.

A few very late ones got them fitted, which is what nerfed the PD and forced the conversion to CR. But DPFs were not in use when PDs were at their best.

And if some people don't do long journeys and hence clog up their DPF, that just shows that the DPF was doing a super job trapping particulates else it wouldn't have filled up.

And those whose engine oil never gets up to temperature, resulting in seriously premature engine failure? Fool them for choosing an oil-lubricated vehicle, eh!!!

That doesn't make the DPF pointless, it just makes it annoying for those people that chose the wrong sort of car.

It wasn't designed to run with a DPF, causes engine-damaging backpressure and kills fuel economy, meaning we're burning even MORE fuel in the first place, therefore it's pointless. I guess the EGR is also a fantastic idea, since it lowers fuel economy even further, yes?

What killed PD is that CR engines give better economy figures and sound less like a tractor. The fact they fall apart at 150K doesn't matter much to people looking in the showroom at a new car.

For the most part, it will fail much earlier... except on Hondas, generally.

Edit: Just looked at what the video was you linked. The thing is, the experts (who clearly see *lots* of these engines) couldn't believe how good the engine looked, which says to me that they see a lot of low mileage engines that are completely coked up and shot and what you see in the video isn't typical.

It's not especially typical for cars like this and the Golf (same engine), which are habitually abused and unmaintained by careless owners... but many an enthusiast reports starship miles and most mechanics will concur that, properly maintained, these engines are bombproof. This was used as one example of what a properly maintained ASZ engine can achieve.

Mercedes used to run a Million Miles Club for those who managed such a distance in their car. Initially the reward was a brand new car of the equivalent model. They stopped that when enough people started achieving the milestone and now you only get a grille badge. Last I heard, they were debating a new badge, for Two Million Miles, as that's now been done more than once, as well. But still, the secret is always to follow manufacturer maintenance schedules.

By the end of the series hardly any of the original car was left, it should have been called "We built a car from scratch around an old death trap".

The suspension (still original) and some of the electrics were a bit knackered and the interior was a touch tatty, but most of it was cosmetic, really. Everything else was pretty decent.

[DanceswithUnix]

It wasn't designed to run with a DPF, causes engine-damaging backpressure and kills fuel economy, meaning we're burning even MORE fuel in the first place, therefore it's pointless. I guess the EGR is also a fantastic idea, since it lowers fuel economy even further, yes?

My CR engine didn't have a DPF (which at 2005 must have been one of the last without it). No engine types were designed to run with a DPF, they just had to deal with it.

Whist they are horribly unreliable, I don't understand the physics of how a working EGR can lower fuel economy. When the engine is near idle and doesn't need much oxygen for combustion, exhaust gas is recycled lowering the oxygen level in the cylinders.

This was used as one example of what a properly maintained ASZ engine can achieve.

*any* modern engine should reach that sort of mileage with good maintenance and specially proper oil changes. I'm used to running old cars, I don't expect the engines to be a problem.

The suspension (still original) and some of the electrics were a bit knackered and the interior was a touch tatty, but most of it was cosmetic, really. Everything else was pretty decent.

The front and back drivers side doors wouldn't open, in some videos you could see him climbing through the car to get out the passenger side. The disks were warped, only one of the windows worked, it wallowed on corners in a way that screams MOT failure so christ knows where he was getting the MOTs from, the aircon had failed, the seats were shot and it smelled.

That is *not* a well maintained car, it is one that did lots of constant speed motorway miles which are kind on engines.

Compare it to my wife's Alfa GT which is only 4 years younger, has only done a quarter of the miles but those are a mix of town driving and sprint racing so a *much* harder life and yet last year it won a local concourse as it is immaculate. I fully expect the GT to last another couple of decades.

[Ttaskmaster]

Whist they are horribly unreliable, I don't understand the physics of how a working EGR can lower fuel economy. When the engine is near idle and doesn't need much oxygen for combustion, exhaust gas is recycled lowering the oxygen level in the cylinders.

https://en.wikipedia.org/wiki/Exhaus...diesel_engines
I know nothing about cars, so I'm sure you're correct, though.

*any* modern engine should reach that sort of mileage with good maintenance and specially proper oil changes.

You're absolutely right.

That is *not* a well maintained car, it is one that did lots of constant speed motorway miles which are kind on engines.

Fine, I take it all back. You obviously know more about cars than me.

[Butcher]

We already covered all that, mate... including bigging up the Octy!

To be fair, that's all you do. The answer to any what car question seems to be Octavia, regardless of actual suitability for the task in hand.

It wasn't designed to run with a DPF, causes engine-damaging backpressure and kills fuel economy, meaning we're burning even MORE fuel in the first place, therefore it's pointless. I guess the EGR is also a fantastic idea, since it lowers fuel economy even further, yes?

So reducing toxic emissions is pointless if it hurts economy eh? Good thing that sort of thinking isn't more popular or we'd still have lead in petrol.

[AGTDenton]

Had a 2013 Octavia 2.0 TDi for 5 years and found it to be a brilliant car. Mapped as well.
Sadly the clutch cylinders were in need of replacement so I decided to trade it in for an anti social car
The Octy had both a DPF and a Turbo with absolutely no issues. I remember the salesman trying to put the fear of god into me about the DPF, but this is a 2nd generation DPF so it revs high at low speed when in need of burning the soot off and keeping the exhaust temps high, and also burns the soot once parked if required. It handled itself very well. Only fear the 1st generation of DPF filters as they don't have these mechanisms in place!

I'm now in the market for a cheap £3k max daily driver for doing what I call dead miles (work).
My picks so far are an Astra Sport Tourer or Insignia estate in diesel.
I would only buy a Vauxhall with the GM era engines! Somehow since becoming Pugs, their efficiencies have gone backwards.
Loved my old 1.3 CTDi Corsa! amazing efficiency 600 miles to a 40ltr tank. That was a Fiat engine.

I do 24 miles a day, just shy of your mileage and a diesel was perfect, 1 fill a month in the Octy! Unless I had other trips. My annual mileage is 20/25k however. I often have many work trips to factor in and all family is up North so it starts to add up.

[Ttaskmaster]

To be fair, that's all you do. The answer to any what car question seems to be Octavia, regardless of actual suitability for the task in hand.

For the most part I stand by that assertion, in the contexts where made, as, to be fair, in those tasks I've yet to find a car that is as good overall... particularly at the sort of price-point usually brought up. I'm sure there are better cars, but for a lot more money.

By contrast, I'm actually a big mkIV Golf fanboy myself, but would never recommend one to anybody. We also have a CR-V, but would rarely suggest anyone but my wife owns one.

So reducing toxic emissions is pointless if it hurts economy eh?

If it lowers economy you're using more fuel and ultimately producing more emissions, so yeah pretty pointless. Obviously there's a lot more science and stuff to it, but that's the basis.

More fuel usage means more oil shipped over on boats that measure fuel economy in gallons per mile rather than MPG, or more commonly tons per hour, which in the case of a fuel ship is around 16 tons per hour or just over 5,000 gallons per hour.... and that's just port to port. You then have the HGV tankers delivering fuel to your station at, what, 6.5mpg on average?

Then you have the folk who just implement DPF and EGR deletes anyway...