What is the difference between a petrol and a diesel engine

facade

What we are telling you is that a diesel is NOT suitable for the driving that you say you intend to do: mainly short distances, so you need to restrict your search to petrol models, which will be cheaper to buy and service anyway, with short mileages you don't need a massively economical car either, you can get a nice comfortable one.



In fact, it is hard to justify the purchase of any new car on economy grounds for short distance driving.

To be extreme, suppose I am lucky enough to have a 1967 Pontiac GTO with the 440 cubic inch V8 and the 3 speed turbo-hydramatic transmission. I might get 8 mpg around town, but if I only drive 16 miles a week, it would only cost £12 a week, or £600 a year. (and the tax is free, and the insurance is a classic policy)

If I bought some eco car, for £6000 that did 80 mpg it would take 10 years driving just to pay for the car, even if the fuel was free.

HoofeHearted

I called in at my local Renault dealer last week to see what cars were available.
The salesman was waxing lyrical about the low emission for the diesel models, and hence low "road tax".

When I mentioned DPF problems on short trips, he said that it was not a problem anymore on new Renaults. He said that the service manager could explain the details to me if I wanted him to.

I declined the offer and walked away.;)

cardinalbiggles

facade wrote: »

If it is a brand new car, you need a petrol engine.
New diesel engines have something called a DPF (diesel particulate filter) to catch the soot. It quickly fills up with soot, and when the car is doing about 70 mph for about 30 minutes it "regenerates"( basically sets this carbon on fire)
They give no end of eye wateringly expensive trouble when used mainly on short trips.

(Naturally, the DPF is a "wear & tear" item that is not covered under warranty.)

Absolute nonsense.

With most systems its related to engine speed and its 2.5k revs for 10 mins.

100k and no problems with mine.

I wish people would stop spouting tripe about DPFs on here based on a few horror stories they hear down the pub. 60% of new cars are diesels in the UK and most now will have DPF filters.

cardinalbiggles

facade wrote: »

They block up completely with soot, then a light comes on telling you to go to the dealer immediately, and the engine goes into limp home mode.

When it goes to the dealer, you give them a wheel barrow full of money, and they plug their electronic gizmo in, simply press a button (must take all of 30 seconds to do), and the car runs at maximum rpm for half an hour (they have to stand them on concrete, as it will melt the tarmac under the car ) this gets the dpf hot enough to burn out all the carbon.

then it is ok again for a few weeks of short trips.

Sometimes they sell you a new dpf, then you will definitely need a large wheelbarrow for the cash

Again total nonsense. Most when they start to get blocked after months of short trips will tell you to run it at higher revs for 10 mins. In the case of the Fiat system it will even do it when stationary.

If you have to force a regen its an easy job and takes 10 mins to do with a 10 quid dongle and some cheap software.

I don't know why people continue to spout drivel about these things.

DUTR

cardinalbiggles wrote: »

Absolute nonsense.

With most systems its related to engine speed and its 2.5k revs for 10 mins.

100k and no problems with mine.

I wish people would stop spouting tripe about DPFs on here based on a few horror stories they hear down the pub. 60% of new cars are diesels in the UK and most now will have DPF filters.

Why is the post nonsense? What benefits is the OP going to experience for his predicted driving pattern?

facade

Passive regeneration takes place at high exhaust temperatures, like those experienced on a long motorway run (the carbon just burns away naturally without help), likely 30 minutes should do it.

Active regeneration, when extra fuel is injected deliberately to raise exhaust temperatures, requires about 10 minutes as you say at around 40mph. If active regeneration does not complete it tries again next trip, and again until either it succeeds, or the dpf reaches the level where it requires a dealer initiated regeneration cycle.

Your trouble free 100k miles simply underlines what we have said: diesels are more suited to high mileage work than short trips.

facade

cardinalbiggles wrote: »

If you have to force a regen its an easy job and takes 10 mins to do with a 10 quid dongle and some cheap software.

But a dealer will ask for at least a suitcase full of money to do this, if not actually a wheelbarrow

You can even remove the dpf and clean it yourself if you are handy with the spanners, there are plenty of youtube videos around.

Mobeer

Don't discount a hybrid for lots of short journeys around town - this is where they excel.

chrisw

cardinalbiggles wrote: »

Absolute nonsense.

With most systems its related to engine speed and its 2.5k revs for 10 mins.

100k and no problems with mine.

I wish people would stop spouting tripe about DPFs on here based on a few horror stories they hear down the pub. 60% of new cars are diesels in the UK and most now will have DPF filters.

I must admit I've had my 5 year old BMW diesel with a DPF since new and due to a change of job 4 years ago I drive 3 miles across town and back every day. I've never had a problem with it, although I do try to take it for a run now and again.

Also, you only ever here from those with problems, not the probably thousands doing like me.

However, given a free choice at the outset, I would probably choose petrol for short trips, as much for the peace of mind as anything.

rexmedorum

chrisw wrote: »

I must admit I've had my 5 year old BMW diesel with a DPF since new and due to a change of job 4 years ago I drive 3 miles across town and back every day. I've never had a problem with it, although I do try to take it for a run now and again.

Also, you only ever here from those with problems, not the probably thousands doing like me.

However, given a free choice at the outset, I would probably choose petrol for short trips, as much for the peace of mind as anything.

I have had issues on my polo bluemotion when i first got it (short trips before starting a job far away) a long run down the mototrway didn't help and needed forced regen. Hasn't given issues since.

Also diesels aren't particularly efficient when the engine is cold!