Petrol v Diesel

walkingbootweather

The time to replace my car is drawing near. Because I cycle, the car only does modest mileage, generally less than 10,000 miles annually, and sometimes the car isn’t used for several consecutive days. Conventional wisdom suggests that for low mileages petrol is a better option, hence I have only ever owned petrol cars in the past.

My simple maths suggest I would save about £600 per year on fuel by swapping to diesel, and that it would take 3 years to recoup the additional outlay, but that then I would probably get a better trade-in on the next car. Friends that drive diesels say that modern turbo diesels are no longer the noisy, smelly machines of yesteryear and that they prefer the driving characteristics and mid-range grunt over petrol.

I’d just about decided to make the switch then someone warned me that the real-world mpg of diesel is often wildly short of advertised, meaning that running costs are in fact quite similar, and that unless you are having regular, long, high-speed runs that the diesel particulate filter can clog up resulting in problems and big bills.

I’m guessing many on here are in the same boat as me, mixing cycle commuting with driving, and doing modest but mixed driving (lots of trips of a few miles, 3 or 4 longer runs every month, and a few major mammoth jaunts each year). Do you drive a petrol or a diesel motor? What would you get in my position? If you have a diesel and don’t do lots of miles, have you had any problems with the DPF?

SimonAH

I haven't had a petrol car as the main car (not counting Minis for playing) since the 90s. A modern turbodiesel is a lovely thing - particularly the ubiquitous 1.9 / 2.0 VAG unit.

My Golf gives me a genuine 58 mpg mixed mileage, and smooth with a capital smoo.

However, for the sort of miles you are planning on doing I don't think it really makes a massive amount of difference - I'd be selecting the car on other criteria personally. (sorry, not a lot of help that :-D )

EKE_38BPM

When I was a WVM I drove a diesel VW Crafter. Most of the jobs were in London, so it was mainly urban driving. Stop-start, 0-30-0mph sprints between the lights, one hour duration journeys.

There was a note stuck to the dashboard telling the drivers that if a certain light on the dashboard comes on (DPF), get onto a fast road sharpish and drive at at least 50mph for about 30 minutes to clear the filter and put the light out. If this wasn't done the filter clogged and the big bills ensued. The vans would do at least 20,000 miles per year, but mainly urban milage.

If most of your journeys are short, urban runs, I think I'd stick to petrol.

Pufftmw

Have diesel, get good fuel economy out of it, pootle around in town around 25mph and never have had a problem with the DPF in the 7.5 years I've owned the car. Last year did under 8000 miles with 1000 of those being commuting I would have said.

bails87

I've got a diesel (1.8tdci focus) and do about 8000 miles per year.

Most of my driving is to work on the days I don't cycle, or 40 mile trips on motorways at the weekends for MTBing/to see friends. Then there's the odd long trip to Wales or oop North for MTBing or down south to see further afield friends.

MPG is claimed at 54.3, I drive 'purposefully' (I'll overtake if needs be, I get up to speed quickly, but don't blast around at 90mph) but smoothly and last time I looked the average MPG over about 6 months was 49 pointsomethnig MPG. If I drove at 60 instead of 70 on the motorway that goes up a lot. I managed over 70mpg on one motorway trip.

As far as the DPF....my car hasn't got one. But if you wait til the engine's warmed up properly and then give it a blast every once in a while it should clear out the soot.

On the noise, there's no denying that mine's a diesel, but then it's high mileage. The noise isn't intrusive and power is delivered smoothly. The 2.7l Audi diesel engine is apparently buttery smooth, no idea if you're looking at a second hand ford (like me) or a brand new Audi/Merc/BMW though.

walkingbootweather

Thanks for replies chaps

EKE_38BPM wrote:

drive at at least 50mph for about 30 minutes to clear the filter

This is what worries me. Sometimes finding a suitable road to do this when needed isn't the easiest thing in the world. I hear that, like catalytic converters, DPFs when they were first introduced caused many problems, but that manufacturers in the most have improved them significantly

mudcow007

We have a 1.9 Vauxhall Signum 150 bhp same engine used in Alfa's, Fiat's etc

we are getting 45+ mpg

most modern diesel engines have a DPF (Diesel Particulate Filter) which basically filters nasty bits from the engine an uses a bit of diesel to burn it off = lower road tax

when the dpf is running it lowers the mpg considerably

our tax is £155 per year compared to £240+ in the 1.8 petrol Astra i had beforehand (37mpg)

EKE_38BPM

walkingbootweather wrote:

Thanks for replies chaps

EKE_38BPM wrote:

drive at at least 50mph for about 30 minutes to clear the filter

This is what worries me. Sometimes finding a suitable road to do this when needed isn't the easiest thing in the world. I hear that, like catalytic converters, DPFs when they were first introduced caused many problems, but that manufacturers in the most have improved them significantly

Yeah, it is a hassle if you are in the middle of London in rush hour and the DPF light comes on.
"Quick, find a road I can do 50mph for half an hour on"
errr...

This was a van, not a car, so I imagine it is a bit more rough and ready than a car would be.

veronese68

I'd go petrol. Friends of mine run diesels and complain about the very narrow power band. 1 of them has a BMW 330 diesel and if it's off boost it's dog slow.
Additionally they are very smooth and quiet inside, but they still sound like an old tractor outside when they start. A neighbour has a beautiful Alfa Brera, but when it starts it sounds awful.
I'd agree with Simon's comments it won't make a lot of difference to you financially, get the best deal you can for something that will make you happy.
I must declare some bias, I work in the motor trade and I quite like cars. I just hate driving in the UK these days. Too many pesky cyclists.

SimonAH

If I were in your boots however I would be looking for a long wheelbase diesel Landrover.

Can take as many bikes as you want, everyone gets out of the way of a battered one, and you can register it as a bus and not pay the congestion charge. Win Win Win

MarksMintness

I don't think you need to worry about DPF's, just give it a good run and during it give it a blast to clear it out as Bails87 has said. Most modern cars should be fine though. Try not to do lots of little crappy runs to the shops as well as some cars don't like that. For generally commuting etc though, diesel is a no-brainer!
Modern diesels are brilliant all round I think.
Cheers

walkingbootweather

@Bails. Sounds like my car usage is similar to yours. My car commute is about 14 miles which takes about half an hour and is about half dual carriageway and half traffic-light-strewn single carriageway. Not sure if that is enough to prevent soot build up or if additional longer trips would be required? I was originally looking at a new family-sized car but seen a few nearly new models from arguably slightly more upmarket manufacturers that seem to be better value.

DonDaddyD

I have a petrol '06 2.0L Mazda 6, I drive it around the M25 to work. I don't drive much so I'm happy with the petrol version. However if I drove on a regular basis and not for "leisure" then a diesel would be where the sensible money is spent.

That said, I've driven the diesel version of my car. It feels completely different to drive compared to mine, less sporty, much heavier, similar power delivery upto 30 though I'd say the petrol is smoother.

The difference in wieght between the two is astonishing and I cannot stress this enough. On the motorway the sheer weight of the diesel would be ideal for that 'holding the road' feeling. Similarly the steering on the petrol is a ta too light for a car that size but this makes it ideal for London.

In short: If I drove on the motorway more often I'd have gone diesel for my car. But if I drove in London all the time there is no way I could live with the diesel version of my car on a daily basis. I get 12-13litres per 100miles in my car (smart brains convert that to miles a gallon).

I've also driven my Dad's diesel 3.0L BMW 5 series. When he borrowed my car he actually returned it complaining that he couldn't afford to drive my car to work after 2 weeks. This is a man who drives his car everyday, everywhere even to the corner shop to get a newpaper.

Depends on the use and combined with the car itself I guess.

daviesee

If you enjoy driving, buy the car that you want to drive.

600 pound over a year is only 12 quid a week.
Given that there are many bargains to be had on "unwanted" petrol cars, is it worth it?
As an example, I saved 10k by buying petrol. That's a whole lot of unleaded.

bails87

walkingbootweather wrote:

@Bails. Sounds like my car usage is similar to yours. My car commute is about 14 miles which takes about half an hour and is about half dual carriageway and half traffic-light-strewn single carriageway. Not sure if that is enough to prevent soot build up or if additional longer trips would be required?

I'd just do what I do, once every couple of weeks give it a good blast, just a 'racing start' and then some high revs, e.g. leave it in 3rd to accelerate up to 60*, rather than changing up to 4th and 5th like on a more leisurely start.

*depends on actual gearing, but you get the point.

Just make sure there's no cyclists behind you who'll be forced to chew through black smoke!

MarksMintness

walkingbootweather wrote:

@Bails. Sounds like my car usage is similar to yours. My car commute is about 14 miles which takes about half an hour and is about half dual carriageway and half traffic-light-strewn single carriageway. Not sure if that is enough to prevent soot build up or if additional longer trips would be required? I was originally looking at a new family-sized car but seen a few nearly new models from arguably slightly more upmarket manufacturers that seem to be better value.

my commute is similar, I'm sure you'll be fine I wouldn't get too hung up about it. As others have said just give it a bit in a gear (not a problem for most folks!)

DonDaddyD

OK I just found out that I'm getting roughly:

12 liters/100 miles = 37.8840833 miles/gallon(UK)

That ain't good, is it?

gtvlusso

Must admit that I am looking into this now:

ML270CDI with 220BHP on tap:

Town - 18 to 20mpg
On a Run - 36mpg

80 litre tank is around £120 to fill - over a complete tank I get 32mpg.

Honda CRV 2.0 Petrol - similiar MPG, smaller tank, but Lower fuel cost = win.

When I look at the trip computer on the car itself, and then I do the maths, the trip is not actually that accurate......

Aside very small cars with massive MPG (I think there is a Fiat that does 70+ mpg) - on average with the cost difference I don't think there is much in it now.......

Hence we consolidated from 2 cars to one car to save money....

jonny_trousers

A useful and timely post for me. Thanks! Need a new car to share with my girlfriend and most people we know were plugging diesel, but neither of us are doing big miles these days. Petrol sounds like it makes sense.

asprilla

DonDaddyD wrote:

OK I just found out that I'm getting roughly:

12 liters/100 miles = 37.8840833 miles/gallon(UK)

That ain't good.

On her commute Mrs A normally gets around 23-24mpg. A quick weekend trip away making good progress down the motorway (i.e. somewhere between 90 and 100 and punching it as required) will normally bring that back up to the high 20's. It doesn't get much better than that.

However, I intend to run this car into the ground and I bought it because I wanted to own a straight six before they became a thing of the past. Between Mrs A and I we do about 12k miles a year.

Pufftmw

Veronese68 wrote:

I'd go petrol. Friends of mine run diesels and complain about the very narrow power band. 1 of them has a BMW 330 diesel and if it's off boost it's dog slow.

I've got a "chipped" Volvo XC70 2.4 with 200bhp & 320 ft/lb. Sure its pulling around 1800kg but I wouldn't call it slow! 0-60 & 1/4 mile times aren't mega but acceleration out of corners and for overtaking is brilliant. It surprises a lot of people including the 3l Z4 that tried to out-accelerate me coming out of Redbridge r/about the other day

bails87

Pufftmw wrote:

. It surprises a lot of people including the 3l Z4 that tried to out-accelerate me coming out of Redbridge r/about the other day

I kept up with a 106GTi, not a supercar, but you'd expect it to be quicker than my old man car! Admittedly the 'race' was 30 to 70, if it was from a standing start he'd have been quicker than me.

veronese68

Anyone else getting the advert for red diesel at the top of the page? That would make a diesel a LOT cheaper to run.
Chipping is cheating. I think that it gets around some of the issues with fuelling that cause some of the flat spots in a standard car. The flat spots are often there because measurements are taken at certain revs, speeds or throttle openings. So, to make the cars pass regs and improve the figures quoted everything gets backed off in the range tested. Get it chipped and it avoids all of that. Also tends to improve economy if you can avoid using the power you have gained. By not racing little sports cars you very naughty man. The only downside to getting a car chipped is that it can impact the life on the injectors. Small price to pay though and insurance companies can't tell as far as I can work out.

Kieran_Burns

My mapped 3.0TDi (280bhp / 400ft/lbs) will return 50+mpg on a long run and always over 30 mpg on my commutes (which are admittedly country lanes) and being a V6 is very smooth.

Plus I've fitted a Milltek twin backbox and it sounds NOTHING like a diesel from the back. cold starts in the morning.... yup: tractor time

Remapping can significantly improve fuel economy but you do need to use the good stuff when filling the tank (not just the 'premium' diesels, just use Shell or BP regularly)

Oh, and the 1.9 TDi, not the 2.0 - the cam pulley on the 2.0TDi shatters causing v expensive repairs

bails87

Yep, I'm also getting red diesel ads.

It was on a 70pmh limit dual carriageway, away from a RAB, I saw him glance over while doing the chav 'one hand on the wheel while leaning back' thing, so put my foot down I stopped at 70, he carried on and vanished over the horizon!

rolf_f

SimonAH wrote:

I haven't had a petrol car as the main car (not counting Minis for playing) since the 90s. A modern turbodiesel is a lovely thing - particularly the ubiquitous 1.9 / 2.0 VAG unit.

How opinions can differ. I've driven a few of those. Possibly the dullest engine in the world for me. How so much power can be so uninteresting to drive I don't know. They are quick but feel terribly slow - joyless engines. I'd have loved to have tried the 1.6 FSi engine. I think I'd have enjoyed that more.

Don't know if the VWs have changed but the engineering on them a few years back was very cynical - the 1.9 ridiculously undertuned compared to the 2.0 with the gearboxes the wrong way round. The 1.9 needed the 6 speed box which wasn't an option - the 2.0 would have been fine with the 5 speed box -which wasn't an option.

Hence I drive an old car with a huge turbo with massive lag - now that feels quick even though it isn't really by modern standards

Pufftmw

Why is chipping "cheating"? I had a custom (to my car) tune, not just an eBay "box" job. It did indeed make it smoother, faster and more economic as it mapped the car better to its capabilities, not just enter a manufacturer "safe, one size fits all" map. I'm just taking advantage of the potential of the car. The £500 cost has more than been recouped in fuel saved.

jonny_trousers

Veronese68 wrote:

Anyone else getting the advert for red diesel at the top of the page? That would make a diesel a LOT cheaper to run.

Yup. The 'new improved' forum obviously has some clever little word recognition thing to tailor the ads to the topic. I noticed the other day how there were ads for a curry house along side the 'best ever dinning experience' thread. I must go back and revisit some of DDD's threads as there could be some very interesting ads chosen to accompany those.

gtvlusso

The ML is remapped from 163BHP to 220BHP.....

More for towing than anything else, but it does change gear allot less - Auto box + tiptronic.

Best things for fuel economy:

1, Tyre pressure - make sure they are at the manufacturer spec
2, Thermostat - is the engine getting hot enough, if the thermostat is knackered the engine will probably be running too cold and consequently fuel economy goes to crap
3, Oil and filters - make sure it is regularly serviced
4, Gearbox oil and filters - most people don't bother, as I am OCD, I do this every 30k
5, Diff oil - I do this every 30K
6, Bearings - grease up and roll on.

walkingbootweather

Rolf F wrote:

Hence I drive an old car with a huge turbo with massive lag - now that feels quick even though it isn't really by modern standards

Not a Saab by any chance Rolf? Actually now that they have gone into administration Saabs do look stonking value, and for the 9-3 at least spares should be OK to get hold of.

CiB

DPFs - I've just been through this so here's my take; it loosely relates to a Volvo S40 2.0D; other diesels are available.

The DPF traps the soot that would normally come out of the back of a diesel's exhaust. After a while the filter clogs and the engine management clears it by increasing the amount of fuel that goes through, and by injecting some additional hyper-expensive fluid to help burn off the particles. This happens every 300-500 miles, or when the sensors decide it needs doing. The number of burn cycles before the filter becomes unusable is limited, with the net result being that the DPF (on my model at least) is designed to last about 75-80000 miles. A new one plus fitting plus the fluid that it uses brings a bill of ~£900 when it's all done, or you can go down the aftermarket route and a cheaper nonstandard one for a lot less. I did that.

Thus if you plan to run a diesel and don't intend to keep it much beyond 3 years from new the DPF issue doesn't matter to you. It becomes someone else's problem. If the light comes on, just drive it somewhere for 30 minutes or so. Doesn't need to be an Italian tune-up (high speed thrash) just long enough for the system to burn off the particles.

MPG wise there's a huge variance depending on the environment. Mine does a steady pootle of 20 miles each way to work at ~40-50mph in traffic, with a half mile of stop start through town and 2 mile stretch of dual c/way where it often sees 90. That's the daily use and returns around mid-40s MPG, which ain't bad for a big heavy car being driven with no real regard to its economy. It uses what it uses, then I put some more in. Round town it drops off the cliff to the mid - low 20s, and that's not racing lights, being first away from stop lines etc, just normal driving. I could get more maybe but tbh I CBA. The difference isn't big enough to make me bother over a year. On the m/way cruising at 70ish it sits at about low 40s MPG, move closer to 80 - 85 and it's down at around mid-30s, so there's some incentive not to go too quick.

To drive though I much prefer the smooth torque of a mid-sized diesel. Passing anything at legal speeds is a doddle; see the gap, 5th or 4th (but not 6th usually) sees the obstacle dealt with,smoothly, quickly, safely with no drama. I've been driving diesels now for the last 7 or 8 years and wouldn't like to go back to a petrol engine.

As a clincher though, diesel is becoming scarcer due to refinery capacity across Europe decreasing, and when refinery capacity reduces it's petrol that takes priority for now. Don't expect to see either the price or the price gap (d v p) dropping any time soon. The premium is there and is likely to stay.