Don't waste money on a diesel car

Research suggests it could take 28 years to recoup the cost of buying a diesel car. We tell you why this supposed greener fuel isn't always worth it...

March is a big month for the motoring world, and as '09 plates hit forecourts up and down the country, dealers and car enthusiasts alike should be rubbing their hands with glee.

But it's very different this year. Production lines across the globe have slowed dramatically, with goliaths such as Toyota posting previously unheard of losses.

Now it seems, manufacturers can't give cars away fast enough, and in some cases you can even buy one car and get another free!

But whether you want a new car, or are content with a used one, there is one other fiercely contested debate when it comes to cars:

Petrol vs. diesel

While diesel is traditionally seen as offering more miles per gallon (mpg) than its petrol equivalent, it also costs around 10 to 12p more per litre at the pumps.

Of course, this wasn't always the case, and until the mid-90s, diesel was actually cheaper than petrol. However, rising demand from countries such as China, combined with a shortage of refining capacity now means buying a diesel car isn't always a no-brainer. On top of the extra fuel costs, most diesel-powered cars are more expensive to buy than their petrol equivalents.

In fact, according to research by car expert Parker's, it could take nearly three decades to recoup the costs of driving one.

Putting diesel to the test

Parker's examined prices for petrol cars and their diesel equivalents. Taking into account the initial purchase cost, fuel consumption, as well as the price of fuel at the pumps, they then calculated how many miles it would take for the average diesel motorist to break even compared to a driver using petrol. The results were astounding.

For example, Parker's calculated it would take a whopping 287,356 miles to break even if you purchased a diesel-powered BMW 318d SE Saloon as opposed to its petrol equivalent. For someone driving an average of 10,000 miles per year, that works out as over 28 years to break even!

Fancy a Mini? Well, according to the research, petrol should be your only fuel of choice, as it will take 99,531 miles to break even if you chose the 1.6D Cooper over its petrol equivalent.

Parker's did find a few cases where diesel models were cheaper to buy. For example, Jaguar's 2.7 diesel Premium costs the same as the XF 3.0 V6 equivalent, while the Mercedes Benz CLS320 CDI costs £700 less than the CGI counterpart. In these cases, diesel makes sense, as better fuel economy will mean you'll start saving from the very first tank of fuel.

If you want to find out how much your diesel dreams could cost you, use this calculator to find out how long it will take to recoup the costs on your selected model.

Fundamental differences

Of course, when it comes to buying a car, it's a lot more complicated than simple number crunching. For one thing, many drivers find there's a significant difference between the stated mpg in the car manual, and what the car actually does out on the road.

Another issue is that diesels tend to retain more value for longer than their petrol equivalents. On the other hand, petrol fans highlight the fact that diesels need more oil changes and are slightly more expensive to service as a result.

The other main difference between the two fuels is environmental.

Fans of diesel usually parade their green credentials at any given opportunity. However, their rise in popularity over the years is probably more to do with tax policies.

Dealing with road tax

During the last budget, our beloved Alistair Darling shook up rules for Vehicle Excise Duty (VED). From April, the current seven road tax bands will be expanded into 13 new bands, favouring cars with lower CO2 emissions.

Drivers of diesel superminis such as the Volkswagen Polo Bluemotion, Seat's Ibiza Ecomotive or Ford's Fiesta Econetic, which all emit less that 100g/km of CO2, will already know what it's like to pay zero road tax.

However, according to Parker's, it will take you 42,890 and 39,335 miles respectively to break even on the Polo and Ibiza petrol models. So, even though you won't have to pay any VED, again you have to ask yourself if the extra costs are worth shelling out for.

Although petrol cars still have some catching up to do when it comes to CO2 emissions, for smaller hatchbacks at least, the gap is closing.

From April, if your car is registered after March 2001 and emits less than 120g/km, you'll pay no more than £35 in VED. In fact, if you own a car that emits less than 140g/km of CO2, your VED will either remain the same, or be lower than last year.

In fact, VED only starts to bite when you start leaning towards large engine and 4 x 4 models. For example, if you had your eye on Ford's family S-MAX 2.5 Titanium, you might want to consider the TDCi diesel model instead.

At £550 extra for a smaller engine, you may not think it's worth it. But with the cars emitting 224g/km and 175g/km of CO2 respectively, the new tax bands mean you'll pay £175 in road tax for the diesel model, and £215 for the petrol.

This leaps to £250 and £550 respectively for new registrations in 2010. So, with the £300 difference in price already eating into any savings from opting for petrol - in this case at least, diesel should be your fuel of choice.

Still, if you're looking to drive a big car, and clock up lots of mileage, diesel is still the way forward. As for the rest of us, I think it's time to get those calculators out, as there's more to petrol vs. diesel than meets the eye.

Prices quoted are subject to fluctuations in the price of petrol/diesel

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