So basically I am shopping for a new car. In this vein I wondered down to my local car garage to look at some. The salesman told me that as I am unlikely to do more than 14 thousand miles a year (I've calculated about 12 thousand) and the majority of my journeys would be within the city I should not get a diesel and should instead get a Petrol car. 

 

His reasoning was that Diesel cars are legally mandated to have a DPF filter, which filters the soot from the engine. If the car doesn't do a lot of long journeys, the soot would build up and the filter could end up damaged, costing more to replace than the savings in fuel from the diesel engine. 

 

Looking at wikipedia it appears the car would require a sustained run of over 40mph to reach the temperature needed to avoid damaging the filter. So what I want to know is, does anyone know how much this is true, and how often I would have to do long journeys in the car to avoid damaging it?

I only know most of this with a dutch point of view. As in our local taxes etc. So i'll try to sketch the picture with that in mind. No idea what is applicable to your situation.

 

In general when buying a NEW car these sort of rules apply:

 

Get a petrol car when you drive less than 25000 km / 15500 miles per year. Get a diesel otherwise. (that is with 100% diesel availability (at all fuel stations) and cheaper diesel than petrol). This is mainly because of a few things, one of which you already indicated. 1 Diesel engines are a bit more expensive than petrol engines, simply because the process is a little bit more complicated, higher pressures etc. 2 Diesel engines are a bit worse for the environment than a similair petrol car. This results in a higher tax you have to pay for a diesel car compared to a road car AND a higher fee to drive on roads. In other words, when you buy it you pay more, and when you drive it you pay more annually (though that varies from country to country).

 

When you buy a used car. There will be a big difference here, in general with the years gone by the petrol car and diesel car will roughly cost the same, the difference in the engine costs will have disappeared by now. There will not be extra taxes because of you buying a "bit more environmentally unfriendly " car because it will be second hand anyway. So you only might end up with a little bit higher taxes because of driving a car like this.

 

I think the salesman who told you the story had parts of the new car story in his mind when talking about the milage and the costs vs benefit situation. There is a kernel of truth to his story about the filter. But as far as i am aware this is not the entire truth neither. A diesel car has this filter in the exhaust system, same as petrol cars having a similar sort of filter in their exhaust system. With the major difference being the sooth of the diesel combustion. Even when sooth builds up, a sustained drive, once in a while, will generate the heat for it to burn of, it will burn off old sooth as well. So yes sooth will build up if you only do short runs. Then again, a petrol car will also start to degrade a little bit over time when doing only short runs. When you do a sustained drive over 40 miles an hour you will notice the petrol car will get more life to it as well.

When you look at all the parcel delivery vans and most taxi's (at least in a lot of places thats the case) most of them will run on diesel. And i don't think the filter will be the major cause of any of their problems.

 

In my experience you would need to take a longer journey like once every 2-3 months to avoid a "build up" but even a longer period of time would not increase the risk by too much.

 

My main reason in choosing between petrol and diesel would be the driving comfort and fuel money for your mileage. The difference in costs between a petrol and a diesel in terms of fuel can be calculated: Petrol would roughly do 15 km / l a diesel would roughly do 20 km/l so when looking at the costs. 1.8 euro for petrol and 1.5 for diesel you look at 15000 miles: 3000 euro for petrol and 1125 for diesel. Next to that i generally just like the way a petrol car performs compared to a diesel car. But there are people who like it the other way around.

 

It turned out to be a bit of a rambling story i hope you find some uses in it here and there. :S

petrol short distances, diesel long hauls. believe that.

 

about the pure damage thing, debatable thou plausible, the filter needs a certain heat from the exhaust itself to work "optimal".

 

isn't petrol cheaper for short drives and small mileage?

Two things up front:

 

I'm not a mechanic, nor really know much about cars

I'm american

 

I have a very good friend who was/is a mechanic.  He always told me a diesel engine has less maintenance over the life of a vehicle versus a petrol car.

 

Also I distinctly remember a science teacher in high school claim that a diesel burns cleaner than a petrol engine.

 

I have no idea what filter you're talking about.  Guess I really didn't contribute much

It is somewhat true that many diesel vehicles/trucks are made to do long-lasting and durable runs. Diesel vehicles generally have more torques than gas vehicles.

 

I think it all comes down to;

 

1) What brand of vehicle? Some brands have better diesel engine-building techniques than others.

2) How long are you going to keep it? If you intend to keep it for a long time, like 5-7+ years, then I would suggest Diesel. Diesel engines seems to be a bit more durable in long runs. (PS: their residuals seem to hold up better as well; buy vs. lease consideration also plays)

3) Diesel is more expensive in short city drives, that's from my personal experience with my friends' vehicles. Ended up paying a lot more in fill-ups during that time. Diesel does amazing when you are on a long-trip.

4) How much is the diesel over at where you live vs. regular petroleum

5) Do you have many gas stations with diesel around you. (I live in one of the biggest towns in the world and I don't see that many choices for a diesel) - Consumer trend/somehwat mistaken belief is that the diesel is really bad.

 

In my personal experience with various cars, I personally would just go with a regular gas vehicle.

Petrol iz heaper per litre here. However because of less mpg its overall cost would be higher and attract z an extra £125 of tax a year. But then the engine iz about £2000 more