What are the pros & cons between diesel and petrol cars?

This could not be a more topical subject, given the shenanigans to which VW have subjected the car buying public. The answer to the ‘petrol v diesel’ debate is now very different from the conclusions of even two months ago. The fallout from the VW scandal will have repercussions on the perceived advantages of owning a diesel car – and those repercussions are continuing to evolve almost daily.

So how do petrol and diesel cars compare?

Petrol and diesel fuel prices and economy.

Fuel is the chief cost incurred in owning any car. According to MoneySupermarket.com, the average motorist will spend more than £100,000 on fuel over the course of a lifetime.

Fuel prices are very volatile but, at the moment, diesel costs about 2.5p more per litre than petrol - or about 12p more per gallon in old money. That means that filling a 50-litre tank in a diesel car costs £1.30 more than in a petrol one. However, the diesel will go farther on every drop of fuel. So, although you would spend a little more at the pump, the diesel travels 25% further on every tank of fuel.

It seems like a no-brainer then. But there are complicating factors. With fuel pricing always favouring petrol, and recent big leaps in engine technology, petrol cars are reaching an efficiency level closer to that of a diesel. Given that fact, there must be a question mark over the diesel price premium that motorists pay – around £1,000 to £2,000 more for diesel models of the same specification as their petrol cousins. On economy alone owners would typically need to cover more than 130,000 miles in the diesel, before the fuel economy/purchase price equation levels out.

If you’re considering buying an ‘eco’ version of a new car, then do check the reviews to see whether it delivers on its claimed savings, against real world driving conditions.

The big change in comparing economy is the growing opposition to diesel cars, due to particulate emissions. At all political levels there is a call to limit their use, or sharply increase costs, to discourage diesel cars. This recent policy reversal can only increase the economic advantage of owning a petrol car. 

Tax, insurance and servicing costs.

Car tax and insurance make a difference, but are small when compared to fuel savings and economy. Diesel engines are inherently more efficient than petrol and they produce lower levels of CO2. Consequently diesels are generally cheaper to tax and insure.

However, the taxation climate is changing. Drivers who were enticed into buying a diesel car by factors like lower taxes (due to CO2 emission), are likely to be hit by additional motoring charges and depreciating values for two reasons. One is that the tax regime will become less favourable as Britain falls in line with EU pollution limits. Britain’s Supreme Court recently ordered the Department for Environment, Food and Rural Affairs (Defra) to set out new plans to tackle nitrogen dioxide (NO2) levels by the end of this year.

Secondly, the VW scandal will have an unpredictable set of consequences as the emission/tax calculation rebalances – almost certainly in favour of petrol.

The difference in servicing costs is negligible overall. Although servicing a diesel engine may be more expensive, this has to be done less frequently. But this, again, could alter due to the fall-out from the VW scandal.

Driving.

How comfortable you are when driving is paramount. Always test-drive a car to see if it suits your needs - petrol-powered cars and diesels have different driving qualities.

Petrol models tend to be faster, smoother and quieter on the whole than diesel. However, carmakers are masking these differences - particularly in upmarket models. They will however have a much lower rev limit than a petrol car. Diesel engines offer increased torque from low revs, which is an advantage when towing or overtaking.

Engineering advances have somewhat blurred the line between petrol and diesel, both in performance and refinement. Today's diesels can be smoother than petrol engines – especially the 2 or 3 cylinder petrol units which are a popular choice for manufacturers looking to boost fuel efficiency.

However, petrol will generally deliver a racier, more exciting drive - especially if the car has been tuned for higher performance.

Emissions and noise.

Without doubt emissions are the Achilles’ heel for diesel cars. Particulate emissions are attracting a great deal of negative press because of the damage to health they are believed to cause. One important factor is the increasing use of diesel particulate filters (DPFs). If your driving is mainly low-speed urban motoring, then this can clog DPF filters, adding significantly to servicing costs. Despite Defra claims that the UK is compliant with EU legislation for "nearly all air pollutants", they face a significant challenge in meeting NO2 targets, under pressure from the courts. Consequently the government is expected to hit owners of diesel cars and trucks the hardest, as they emit the largest amount of NO2. Following the VW engine rigging revelations, drivers may be facing higher fuel and road taxes, charges to enter cities and larger towns and could even be offered incentives to scrap their diesel vehicles altogether.

London Mayor, Boris Johnson, is particularly hostile to diesel cars. London is introducing an Ultra-Low Emission Zone from September 2020, with drivers of cars falling below pollution standards forced to pay a £12.50 charge to enter the city. Diesel owners in Islington will have to pay an additional £96 for a parking permit from next month, with Hackney set to introduce a £50 surcharge from 2017.

The anti-diesel movement is growing and other UK cities are expected to introduce similar schemes soon.

Depreciation and resale.

Depreciation is the biggest cost in car ownership over time. Resale value should play a big part in your decision on whether a petrol or diesel car will be more cost-effective overall.

There are more than 11 million diesel cars on Britain’s roads - around a third of all vehicles. Although diesel cars have generally retained their value better than petrol, there are potential problems that can tip the balance. Diesel-powered cars are still slightly less reliable (statistically) and are potentially more expensive to repair if anything serious goes wrong. Particulate filters can get clogged, and cost thousands of pounds to replace. Naturally, these factors affect resale value.

However, it is the VW rigging of diesel engines’ emissions which is likely to have the biggest impact on resale values. It is estimated that 1.2 million cars in the UK face recall (one in 10 diesel cars on the country’s roads). The VW device concerned switched engines to a cleaner mode during official tests, but once on the road, the cars produced nitrogen oxide pollutants at up to 40 times the legal standard.

Owners may find that this affects their car’s resale value. The full implications of this scandal will continue to develop for quite some time.

Conclusion.

If you need to carry loads, or tow them, then diesel is still a good option. However, the ground is shifting. The increasingly hostile environment towards diesel engines, political opposition, potential big increases in charges and taxation, the as still unclear impact of the VW affair on resale values – they all conspire to make the diesel option increasingly risky over the medium and long term.

If you really can’t decide then remember many makes come in both petrol and diesel options.

Take the new Honda Civic available in both fuel options.

Delivering 120ps of power, the Honda Civic 1.6 i-DTEC diesel engine provides class-leading balance of power and economy. The numbers are impressive, with fuel efficiency of 3.6 l/100km and low emissions of 94g/km of carbon dioxide, but it’s the day-to-day thrill of driving it that really excites.

The smaller 1.4 i-VTEC petrol engine offers surprising response out on the road. Meanwhile the 1.8 i-VTEC petrol engine packs a punch while offering the fuel efficiency of a smaller engine.

Whichever one you choose, you’ll enjoy outstanding fuel economy, excellent performance and cleaner emissions. That’s power and performance working in harmony.