Petrol vs Diesel Cars Update


Is it worth running a diesel car? It's a question we have to return to because car prices change, car efficiency changes and fuel prices change. So lets look at the differences for a small car, medium car and MPV.


Today at my local petrol station petrol costs £1.369p per litre and diesel is £1.419p per litre. 1 Imperial gallon = 4.54609188 litres. So petrol costs £6.22p a gallon, diesel £6.45p down the road from me.


How does a VW Touran TDI compare with their petrol option?

A VW Touran SE 1.4 petrol 140 PS is £21915 today and returns a combined 41.5 mpg. The 2.0 diesel in the same trim costs £23230 and does 53.3 mpg. There's no difference in their maximum speed or acceleration. There's only a small - 159 vs 140 - difference in emissions. There's a £1315 price difference in the cars to be recovered by savings in fuel costs.


12,000 miles per year / 41.5 mpg means 289 gallons at a total cost of £1797.58p for petrol. At 53.3 mpg you need 225 gallons of diesel which costs £1451.25p. So you save £346.33p for every 12,000 miles with a diesel. Which means you have to do 45463 miles before the difference in the cost new is recovered by fuel savings.


You might be told the diesel will have a stronger residual value which will return part of the cost new difference but I can say after 43 years experience nobody knows what the used car market will be like it say 4-years time. It will depend on the differences in the price of diesel and petrol, supply and demand plus the actions of millions of buyers and hundreds of thousands sellers. The used car market is a real market place. That's without considering wider environment issues like the law, taxes, politics, the economy, innovations etc.


Let's move on to a medium small car. A Ford Focus Zetec 1.6 petrol 125 costs £17500 today and returns a combined 47.9 mpg. The Ford Focus TDCI 1.6 diesel 115 in the same trim costs £18495 and does 67.3 mpg. There's no real difference in their maximum speed or acceleration. There's only a small - 136 vs 109 - difference in emissions. And there's only a £995 price difference in the cars to be recovered by savings in fuel costs.

12,000 miles per year / 47.9 mpg means 250 gallons of petrol at £6.22p total cost of £1555.00p. At 67.3 mpg you need 178 gallons of diesel at £6.45 which costs £1148.10p. So you save £406.90p for every 12,000 miles with a diesel. Which means you only need to clock up 29343 miles before the difference in the cost new is recovered by fuel savings.

Right now a Focus looks viable value either way. It seems savings with a Touran diesel are soaked up partly by VWs price difference.

Does it get even better with a small car?

A Vauxhall Corsa is for sale with a confusion of trims, engines and marketing programmes. Let's zoom in. A Vauxhall Corsa SXi 1.2 petrol costs £13520 today and returns a combined 53.3mpg. The 1.3 diesel 95 in the same trim costs £15450 and does 64.2mpg. There's only a small - 124 vs 115 - difference in emissions. There's a £1930 price difference in the cars to be recovered by savings in fuel costs

12,000 miles per year / 53.3 mpg amounts to 225 gallons of petrol at £6.22p total cost of £1399.50p. At 64.2 mpg you need 187 gallons of diesel at £6.45 which costs £1206.16p. So you save £193.34p for every 12,000 miles with a diesel. Which means you need to clock up a massive 99824 miles before the difference in the cost new is recovered by fuel savings. Lucky you get their lifelong guarantee. It doesn't matter if you compare the more expensive 1.4 petrol with less powerful cheaper diesels. Something's up. Either the diesel doesn't make a good enough difference or your savings are being sucked up by Vauxhall's diesel price.

My examples don't support this but a large car is normally a more viable proposition with a diesel engine. Many SUVs don't have a petrol alternative. You're better off with petrol in a small car. Diesel is not an option with some small cars. But to go back to the beginning, car prices change as does their efficiency so you need to work it out every time. You're going to see some amazing changes in car efficiency especially in energy recuperation and dual function components.

But it's not just about the figures. Diesel was a smelly, sluggish option that was noisy and vibrated. They're not so smelly these days. Turbo technology has improved performance. They're still noisy though less so with common rail injection and they still vibrate it's just manufacturers isolate or insulate you from the noise and vibration. Diesels have 3 to 4 times the compression of petrol with great torque and a 1.9 can feel like a 2.7 petrol. So there are tastes and qualities to consider. Whichever side of the fuel pump you normally pick the above will probably change nothing.

However keep informed to save real motoring costs

Regards
Ralph