Petrol or diesel?

There are pros and cons to each type of engine depending on how much they cost to buy and run, how they feel to drive and their effects on the environment. So this should help explain the top 10 things you need to know when deciding between a petrol car or a diesel car with the help of two cars.

1) Demonisation

There have been long these stories recently demonising diesel engines, and it all pretty much started with the Volkswagen emissions scandal, and there’s also the environmental and health implications of course which have also been in the press a lot recently. To explain briefly, diesel engines give out more small particulates than a petrol engine, the older diesel engines are the ones that are the worst culprits for this, the very latest modern diesels are fitted with particulate filters to help reduce the amount of particulates that are being emitted into the environment.


2) The environment

A petrol car will emit more carbon dioxide (CO2) than the equivalent diesel and CO2 is a greenhouse gas which causes climate change. However, while diesels may emit less CO2 than a petrol engine, they actually emit more nitrogen dioxide (NO2) and that can cause smog, acid rain and respiratory problems in humans. In other words diesels are worse for the immediate health of people while petrols are worse for the long term health of the planet.


3) Adblue

To help combat the harmful NO2 emissions, certain diesels use a system called Adblue. This inexpensive liquid reacts in the cars exhaust system with the nitrogen oxide gases to produce harmless nitrogen and water vapour. This system isn’t actually used on all diesel cars but something like a Citroen C3 1.6 diesel does, you actually add this to a separate tank it doesn’t go in with the fuel and you probably have to top up the car once every few thousand miles. You can either do that yourself or you could ask your franchise dealer to do it for you.


4) Popularity

The popularity of diesel cars has reduced in recent years. In 2011 the market share of diesels was 51% but now, then years later, it’s down to 44% and we’ve seen the number of orders for diesel engine cars has dropped by 10% over the past year.

5) Price

As an example, the top of the range Renault Kadjar with a 1.2L (130hp) turbo petrol engine. With a manual gearbox it will cost you around £25,000. But if you get the exact same car, but with a 1.5L diesel engine with (110 hp) it’ll cost around £27,000. That means that the diesel costs about £2000 more than the petrol for this model. Now the price differential changes depending on which manufacturer you’re talking about but, generally speaking, a diesel will cost you more to buy than the equivalent petrol.


6) Cost

Obviously the main reason that you would pay extra for a diesel is because it’s going to be less expensive to run, but first let’s consider some of the costs. In terms of servicing there’s actually nothing in between the diesel Kadjar and the petrol one and in terms of insurance they’re very similar. In terms of taxation, in the first year the diesel one will cost £140 and the petrol one will cost you £160, but every year after it will cost the same £140. So really, it all comes down to your fuel bills. Renault says that this diesel car will do 72mpg (miles per gallon), this petrol one however does 50mpg.


7) Breaking-even

Now we all know that it’s actually pretty hard to get close to those claimed manufacturer’s fuel economy figures in the real world. For instance, in a week-long test, the 1.5L diesel actually averaged 55mpg and the 1.2L turbo petrol was averaging just over 35mpg. That means your £50-worth of fuel in this diesel would actually take you 497 miles, whereas £50-worth of petrol in the 1.2L engine that will only take you 327 miles. Based on those figures, if you do the math, you’d have to do 38,000 miles in order to recoup that £2000 pounds that this diesel cost more than the petrol, in terms of fuel savings. So you’ve really got to think long and hard about the kind of milage you do, and how long you plan to keep the car as to whether it’s worth paying the extra for the diesel


8) Diesel

Running costs are only part of the story when you’re deciding whether you want a diesel or petrol engine. For instance, they do feel a bit different to drive. A diesel produces most of its power low down the rev range, looking at the performance using specific data equipment, the 0-60pmh time for the Renault Kadjar diesel was 11.7 seconds. However, in the real world you’re not really going to be doing that very often. What’s more likely is you’re going to be sat on the motorway, cruising along in top gear and you want to overtake somebody. So what we did was time the car from 60mph, floor it, and see how long it took to get to 70mph, a classic overtaking maneouvre. The diesel car got from 60mph to 70mph in 7 seconds which is not that bad.


9) Petrol

The petrol version of the Kadjar I should point out had the automatic gearbox, but the automatic gearbox has pretty much the same economy as the manual and also gives similar performance as well.  The 0-60mph time was 10 seconds flat, so just under 2 seconds faster than the diesel but how about in-gear, accelerating on the motorway. In the petrol version, the speed builds slower and going from 60-70mph took 8.5 seconds, a second and a half slower than the diesel. So essentially, if you like to be fast away from the light starts as in, you drive in town quite a bit, get the petrol. If you want effortless overtaking on the motorway, or you do a lot of miles, get the diesel.


10) Comfort

Another thing to consider when choosing between the petrol car or diesel car is your comfort. So petrol engines are generally quieter and they’re smoother. If you compare it side-by-side with the diesel, you’ll hear almost immediately that it’s quite a bit louder and vibrates a lot more. They aren’t as smooth and they’re nowhere near as quiet. Then there’s the fuel itself, if you get it on your hands diesel is really quite smelly even smellier than petrol.

I hope this has helped explain the pros and cons between buying a diesel or a petrol car, and has allayed some of your fears surrounding some of the media coverage about diesels. Remember most of the problems relate to old diesels so you shouldn’t rule out buying a modern diesel car entirely, it could still work out the most ecological and economical option for you.