Which is cheaper to run - petrol or diesel?

WIAWSNB

Or, more precisely, by how much? Given, say, an 8k annual mileage.

I know diesel is significantly more economical, but also costs more at t'pump. Diesel engine services are dead simple and cheap - how much more will a petrol service be? 

(Not bothered about PDF and all that malarkey.)

I much prefer a diesel - torque, economics, reliability - but should really be open to petrol alternatives to keep my options as wide as possible. Eg, Mazda CX5 - 2 litre nat-asp petrol vs 2.2 diesel.

Thanks for thoughts and insights

MattMattMattUK

WIAWSNB said:

Or, more precisely, by how much? Given, say, an 8k annual mileage.

I know diesel is significantly more economical, but also costs more at t'pump. Diesel engine services are dead simple and cheap - how much more will a petrol service be? 

(Not bothered about PDF and all that malarkey.)

I much prefer a diesel - torque, economics, reliability - but should really be open to petrol alternatives to keep my options as wide as possible. Eg, Mazda CX5 - 2 litre nat-asp petrol vs 2.2 diesel.

Thanks for thoughts and insights

It is not a valid question as there are too many variables.
Total miles driven, mean, median and distribution of journey length, roads driven, traffic, driving style, load, towing and all that before you even account for the difference between two different engines operating on the same fuel.

As a very simple guide, if you do a lot of miles and most of them are driving at a relatively consistent speed then diesel will be cheaper, if you do not drive a lot of miles, if it involves a lot of stop start traffic then petrol will be cheaper. If you tow a lot then diesel will probably be cheaper. If you are heavy footed then both will be equally bad. Generally petrol is more responsive, even with dual turbo diesels.

If you want lots of torque, good acceleration, cheap servicing and very cheap per mile costs then an EV is the way to go.

Mark_d

It depends very much on the car and the type of driving.  If you have a heavy estate car and the majority of your 8k miles are motorway driving, then diesel would be cheaper.

Diesels have suited my style of driving in the past.  I don't have a  car at the moment but if I was to buy one, it would be a petrol hybrid.It's a different type of driving but we have to get used to the future

Stubod

Some petrol's can be more economical that diesel, I get 70mpg from a self chatge hybrid with non of the potential dpf problems associated with low mileage diesels. Prior to that I changed from a 2 ltr diesel Octavia to the 1.4 turbo Octavia petrol that basically had very similar performance and virtually the same mpg.

Up until about 7 years ago all my cars were diesel, however I would not now buy another diesel car.  

Keep_pedalling

Not sure why you think servicing costs for petrol cars is going to be more expensive, a quick Google suggests the opposite. The same seems to be the case for reliability with modern diesel engines which are far more complex than older ones. 

https://www.carwow.co.uk/guides/choosing/petrol-diesel-878#gref

daveyjp

A modern hybrid with an autobox negates any discussion about diesels having better torque.

The hybrid motor gives the low speed shove diesels are known for and as above you will get 65+mpg without trying.

facade

If you want Mazda, the most reliable engines are the Skyactive-G NA petrol. They also use TC auto gearboxes for extra reliability.

The diesels have a very poor reputation, most likely any fuel cost saving from a diesel will be more than offset by the repair bills!

Mildly_Miffed

WIAWSNB said:

Or, more precisely, by how much? Given, say, an 8k annual mileage.

I know diesel is significantly more economical, but also costs more at t'pump. Diesel engine services are dead simple and cheap - how much more will a petrol service be? 

(Not bothered about PDF and all that malarkey.)

I much prefer a diesel - torque, economics, reliability - but should really be open to petrol alternatives to keep my options as wide as possible. Eg, Mazda CX5 - 2 litre nat-asp petrol vs 2.2 diesel.

It's impossible to say. It's entirely down to reliability - and if you're "not bothered about" DPF, I presume you're looking at cars at least 16yo, because DPFs became ubiquitous with Euro5 emissions in 2009 or so. Then add Adblue for almost all diesels under 10yo, Euro6 emissions. If you're looking pre-2017, then CO2 taxing is relevant.

There's not a lot of difference between a diesel and a petrol service these days, with ignition being computerised and plugs needing replacement every 100k miles or so.

The difference between the two fuels can only be a few pence per litre. I filled up yesterday with diesel at £1.399, unleaded was £1.359.

Let's work a ballpark 45mpg, so 10 miles per litre - 800 litres per year. You're talking about £32 difference on £1100 expenditure.

If you're talking about the difference between 40 mpg @ £1.36 and 50mpg @ £1.39, then you're looking at £1220/year for petrol vs £1010 for diesel. £200/year difference. It's a trivial difference, easily wiped out by one bill for maintenance or repair.

Herzlos

Diesels take a while to warm up to reach efficiency, so if you're doing a lot of small journeys where it's not getting warm you may find better fuel economy from petrol. The same journeys will also not be any good for the DPF and if that gets irrepairably clogged the replacement will wipe out any savings. 

Most of them also have expensive adBlue systems to keep the emissions down. It's only about £20 every few thousand miles to top up but again a failure in the system will wipe out any savings. 

I'd go petrol (or electic) unless you were doing mostly long journeys or otherwise really needed a diesel.

remoteninja

Generally, diesel is always cheaper if you compare by litre. But then vehicles that use diesel have a higher CC. Unless you compare with a higher CC petrol car. 

WellKnownSid

We've run only diesels for almost 25 years but they are dead now.

My last diesel-engined small 7 seat MPV averaged around 16p per mile (fuel cost)

My current (larger) petrol hybrid 7 seat MPV is working out around 10.5p per mile.  Much better drive than the diesel - instant torque from standstill, no hesitation, feels similar to a three litre n/a petrol.

We've also had an electric car for two years which costs us under 2p per mile

I now cry inside when I visit the petrol pump, so we tend to only use the 7 seater when we absolutely need the extra space.  Last fill-up cost me nearly £60 - which would take us over 3,500 miles on electric.