Diesel vs Petrol, a Quick Comparison

Posted by Thame Cars on Jul 5, 2017 3:48:22 PM


So many times people ask me ‘What car do you drive?’ then go to ask ‘What engine? Petrol or Diesel?’ I just wonder why it even matters which type of fuel it runs on.

If you’re anything like me you probably have no idea why everyone is making such a huge deal about the price changes in diesel, but surely that doesn’t affect me- I drive a petrol, I’ve had a diesel in the past and I really can’t tell the difference.

I’m one of those people who likes to have knowledge about everything (sometimes I’m clueless and just try to sound convincing). I hate being that person at a dinner party when a topic comes up and you have no idea why it’s such a controversial topic, and I just imagine the debate of petrol and diesel being one of them.

So over the past weeks I’ve been researching all those provoked questions in my mind about petrol and diesel; the difference between them? Which one is better? Why a sudden drop in fuel prices?

I’m not even going to go into hybrid or purely electric because that a topic for another day, but I will do my research on those too in the near future and share it with you.

I’ve never really understood the difference between cars that run on petrol and cars that run on diesel. Well they are both different sources of fuel, they just differ in the ways that they behave in the engine.

A petrol engine has pistons which go up and down and compresses the mixture of petrol and air, just before the piston hits the top of the cylinder the spark plug kicks in, igniting the fuel and air mixture rapidly.

Whereas a diesel works on compression of the gases to ignite the fuel in the cylinder, if you have a turbo charger on your engine then there is more force through air on the cylinder as the pistons go up and down. (Sounds quite scientific, but it’s really simple).

The easiest way to explain is that petrol engines have a spark plug and diesels don’t.

Fuel economy is a major consideration when buying a car. One of the most common questions car buyers in the UK ask is ‘Should I buy a car with a petrol or diesel engine?’ Well there is no simple answer it all depends on a number of different factors.

False economic arguments

I’ve had family and friends tangled up in what I’ve now realised is false economic arguments when they are trying to choose between petrol and a diesel when it comes to buying a new or used car.

The choice of engine which is most suitable for you is actually mostly dependant on your individual needs and driving style. Having done all my research I’ve realised that finding the perfect car involves understanding the usage you get out of your car.

So should you buy a petrol or diesel car?

I’ve gathered that your decision should be based on three simple questions:

1) How many miles you will do in a year, and will you do enough miles in order to save more than you will spend on the car?

2) How long do you plan on keeping the car?

3) What will your car be used for more? Urban / town driving or long distance. (I’ll explain why later).

It’s essential to consider how you will really use your car for as long as you own it, but here’s a quick break down of all the generic differences;

  • A petrol engine is more responsive at low revs, so when you pull away its usually quicker, a diesel engine has to work harder so uses more fuel to keep up.
  • A diesel has more torque than a petrol so it will maintain its performance and economy much better even with a full load on the motorway and long distances, where as a petrol will struggle noticeably.
  • A diesel will be more economical on a motorway and when at its most optimal point, where as a petrol engine must try considerably harder to maintain its momentum therefore use more fuel.
  • Short journeys are inefficient to both engines, as cold engines use more fuel and pollute more than warm engines. It can take nearly 15 minutes before fuel economy starts to hit its best figure.

So what I’ve gathered from everything, if you must use the car for short trips, a petrol tends to be a better option.

This is because modern diesels are fitted with diesel particulate filers (DPF) and they trap particles of soot in the exhaust system. The soot particles need to be burnt off, in order to this this the car needs to have warmed up properly – which happens when the car travels at 50mph for longer than a half hour.

If you only do short trips, then just remember your DPF blockage could be a costly problem if you’re not taking a diesel for a long drive every week or so.

So maybe just think carefully about how you use your car before choosing what type of engine powers your next car.

Here’s a little video that you may find quite helpful when choosing your next car. Click here to watch!

P.S If you do go for a diesel remember the prices have dropped, but I can’t seem to figure out why. Either supermarkets are having a price war, or they are actually doing diesel drivers a favour and reducing the prices to help those travelling in the summer. Another conspiracy is that diesel has always been over priced and the price cut has been a long time coming.

Read about the right family car, here

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