Petrol vs Diesel Cost Debate

SlimTheBills

I've often wondered what the financial benefits are to owning and running a diesel car, is it cheaper or not? So, after many sleepless nights thinking about it I decided on doing a few calculations...

I decided to compare two ordinary cars that we comparable in performance from the same manufacturer. They were:

Astra Club 1.7 CDTi 16v
List Price = £18,300 : MPG 62 : 0-60 12.0s : BHP 108
Astra Club 1.6i 16v VVT
List Price = £16,730 : MPG 43 : 0-60 10.9s : BHP 113

(Data taken from Vauxhall and Parkers websites)

So, calculating the total miles per tank (52L) I converted litres to gallons first. 52L = 11.44G. Then multiplying this up by the MPG gives:

Petrol = 492 miles : Diesel = 709 miles

(Now I don't imagine for a minute that these are accurate true driving representations, but it's the only data I could find to work on.)

Let's assume that diesel costs 10p more than petrol. I priced petrol at 90p and diesel at £1. This produces a cost for a tank full of fuel at:

Petrol £46.80 : Diesel £52.00

Divide this my the miles per tank above, gives the pence per mile at:

Petrol 9.51p : Diesel 7.33p

Now lets assume that you do 12,000 miles per year, then the total fuel cost would be:

Petrol £1,141.20 : Diesel £879.60

An annual saving of £261.60 for the diesel. However... the car cost £1,570 more in the first instance. So dividing this into the cost differential will give the number of years you have to have the car in order to breakeven, which calculates as:

6 YEARS!

Even at 20,000 miles per year it is still 3.6 YEARS.

Why should we buy diesel cars?

Mark_Hewitt

I do wonder. Since my diesel Fiesta is giving petrol like MPG

DGJsaver

SlimTheBills wrote: »

I've often wondered what the financial benefits are to owning and running a diesel car, is it cheaper or not? So, after many sleepless nights thinking about it I decided on doing a few calculations...

I decided to compare two ordinary cars that we comparable in performance from the same manufacturer. They were:

Astra Club 1.7 CDTi 16v
List Price = £18,300 : MPG 62 : 0-60 12.0s : BHP 108
Astra Club 1.6i 16v VVT
List Price = £16,730 : MPG 43 : 0-60 10.9s : BHP 113

(Data taken from Vauxhall and Parkers websites)

So, calculating the total miles per tank (52L) I converted litres to gallons first. 52L = 11.44G. Then multiplying this up by the MPG gives:

Petrol = 492 miles : Diesel = 709 miles

(Now I don't imagine for a minute that these are accurate true driving representations, but it's the only data I could find to work on.)

Let's assume that diesel costs 10p more than petrol. I priced petrol at 90p and diesel at £1. This produces a cost for a tank full of fuel at:

Petrol £46.80 : Diesel £52.00

Divide this my the miles per tank above, gives the pence per mile at:

Petrol 9.51p : Diesel 7.33p

Now lets assume that you do 12,000 miles per year, then the total fuel cost would be:

Petrol £1,141.20 : Diesel £879.60

An annual saving of £261.60 for the diesel. However... the car cost £1,570 more in the first instance. So dividing this into the cost differential will give the number of years you have to have the car in order to breakeven, which calculates as:

6 YEARS!

Even at 20,000 miles per year it is still 3.6 YEARS.

Why should we buy diesel cars?

Quality , well done Sir , right or wrong a good read (sort of as i have a v reg 2.0 diesal astra , i like th ecar but i am FAR from convinced it gives me any better economy than a petrol version , round town anyway)

LandyAndy

Low mileage private users buying new cars will be better of buying petrol.

High mileage, mostly business, users buying new will be better off with diesels.

In the second hand market the situation is different.

1. The purchase price differential will have been eroded making the payback period shorter.

2. In many cases people don't think 'Should I buy a 5 year old petrol for £5000 or a five year old diesel for £6000?' They think 'I've got £5000, should I buy a 5 year old petrol or a six year old diesel?' ie they buy the more economical car and discount any, probably small, differences in service costs.

Hintza

Round about way of getting there. No need to go into size of tank etc.

Just taking your figures:-

CDTi = 62mpg
1.6i = 43mpg

1 gallon = 4.561 litres

12,000 miles

Petrol £0.90
Diesel £1.00

Therfore:-

CDTi:- 12,000/62 = 194 gallons = 869l x £1= £882
1.6i:- 12,000/43 = 279 gallons = 1,273 x £0.9 = £1,145

And just to add to your conclusions there tends to be more to wrong on a diesel so servicing can be more. And you have the dreaded dual mass fly-wheel which can cause problems on some cars.

One thing you did omit though is your diesel car will hopefully be worth a bit more in residual value if/when you come to sell it. The question is though will that second hand premium remain in the future?

Lemonade_Pockets

Yep bang on sir. I lost count of how times i had to write this down for customers that were adamant they wanted a diesel to save millions of pounds a year. Despite doing 5kpa and changing a car every 2years.

However as one person has added the only factor to bear in mind is for a lot of marques (especially larger ones) the additional premium for diesel is largely recouped when it comes to resale time. Especially if it has done "petrol" mileage.

Hotspur

Based purely on the figures quoted petrol is cheaper for normal motoring however as Hintza and Lemonade pockets have stated the residuals should be more for the diesel come sale time.
You also have to consider servicing costs as well and that may be less for the diesel.

But how many people buy cars based on economy alone? It was one of my considerations but performance was another which was how I came to drive my GT TDi rather than a petrol with similar performance costing ££'s more.

vansboy

Pretty much the recognised decision for diesel over petrol, was once you were covering 15000
miles/year.

It's still a reasonably accurate assumption, even with the current fuel cost disparity.

HOWEVER, many people who bought ex-fleet, not always high miler examples, either, are finding that the extended service intervals offered on modern vehicles, really only benefit the fleet companies balance sheets, for their time owning the car.

There are some nasty surprises lurking, if something a simple as using the correct oil, at the correct intervals.

Let alone DMF failures - do a Google search on it, as most people will have no idea what this is. & I'm not trying to be clever, or sarcastic, as just a few years back, not many mechanics would know, either!!

& then there's the cars, which have been mis-fueled, or turbos burned out, or....

You might just find a big engined PETROL, is actually a Moneysavers wise choice!!

VB

Pew_Pew_Pew_Lasers!

On the motorway if I had a choice between a revvy petrol engine or a torquey diesel, I'd take the latter any time.

Unless the petrol was a 4.0 V8.

rsvtoddy

VB

Think you mean 15,000 not 150,000 miles per year!:rolleyes:

Woby_Tide

all depends on the cars and the drivers. The engine in one of the OPs models we had in our last car, contrary to the 43MPG our combined driving styles got about 30MPG on average. We switched to a 1.6 HDi with a different manufacturer that claimed about 50MPG, we manage about 44MPG combined.

Not sure what the price difference would have been on the two models, or how it has transpired financially but we would rarely be left with much money from the £125 we set aside for petrol each month with the old car. With the new car we have about £40-50 left on average each month (fill up about 3 times every 2 months at £50 a go.

Eitherway, on a 10k average mileage I certainly have noticed the difference on the fuel bills even with teh extra we paid upfront, as long as we retain the car for 3 years we more than make up for it in my eyes