Diesel or Petrol

Username03725

Goudy said:

Excess soot in the DPF from failed DPF regenerations is only the start of the problem for modern diesels.

....

 

Blimey you're a glass half empty merchant. Millions of diesel engines cover millions of miles without issue. Some fail, just like some petrol engines fail. Personally I don't worry about it - look after it, keep up with the service requirements and enjoy it.

WellKnownSid said:

chrisw said:

I had the EGR valves and coolers replaced twice on a Volvo under warranty. The dealership suggested that, despite the long distances covered, it was driven too carefully and needed to be driven much harder.

I will second that.  I was told my careful driving was why my EGR blocked multiple times - 15 years and 500,000 miles in various diesel cars later I've never had an EGR/DPF problem.

Agreed. My Volvo was intended for long commutes but then the pandemic put the mockers on that so it's mostly shorter trips these days. I 'get a move on' without being silly plus the occasional longer trip, and it's still fine.

sevenhills

WellKnownSid said:

chrisw said:

I had the EGR valves and coolers replaced twice on a Volvo under warranty. The dealership suggested that, despite the long distances covered, it was driven too carefully and needed to be driven much harder.

I will second that.  I was told my careful driving was why my EGR blocked multiple times - 15 years and 500,000 miles in various diesel cars later I've never had an EGR/DPF problem.

What did they mean by 'careful' driving, do you think they were just making excuses, did you stop driving carefully?

Ditzy_Mitzy

Petrol all the way.  Less to the gallon, granted, but sometimes not much less and kinder to the environment.  Less smell, no black smoke and no greasy hands at the filling station.  Quieter, more refined, simpler and no tractor like chug-chugging idle.  Nothing quite beats sticking a petrol car in third, leaving it there and really opening up the engine.  

Goudy

Username03725 said:

Goudy said:

Excess soot in the DPF from failed DPF regenerations is only the start of the problem for modern diesels.

....

 

Blimey you're a glass half empty merchant. Millions of diesel engines cover millions of miles without issue. Some fail, just like some petrol engines fail. Personally I don't worry about it - look after it, keep up with the service requirements and enjoy it.

WellKnownSid said:

chrisw said:

I had the EGR valves and coolers replaced twice on a Volvo under warranty. The dealership suggested that, despite the long distances covered, it was driven too carefully and needed to be driven much harder.

I will second that.  I was told my careful driving was why my EGR blocked multiple times - 15 years and 500,000 miles in various diesel cars later I've never had an EGR/DPF problem.

Agreed. My Volvo was intended for long commutes but then the pandemic put the mockers on that so it's mostly shorter trips these days. I 'get a move on' without being silly plus the occasional longer trip, and it's still fine.

More a realist.

Emission devices on diesels are active systems and as such have more chance of going wrong than passive systems fitted to petrol cars.
As you write, millions of diesels do millions of miles without issue, but lots do only few miles with issue, many due to their active emission controls.



I wonder why it's suggested that you don't drive it carefully or don't hang about.
I guess they don't mean drive it carelessly and speed.

Or do they mean drive it enough to get it all hot enough to start a DPF regeneration cycle and long enough for it to complete, otherwise there could be problems?

Seems a bit odd, making an efficient engine and then having to drive it otherwise to make sure it works properly. 

Grumpy_chap

sevenhills said:

What did they mean by 'careful' driving, do you think they were just making excuses, did you stop driving carefully?

Ah-Haaa
You've identified the car industry cunning plan, Baldrick.
They build cars that are not suitable for long mileages then encourage you to drive it like you stole it.  Hence, the devious         scheme is never uncovered because you smashed it up so no-one ever knew the emissions control devices would cause the car to have problems.

plumb1_2

I suspect the problems with the vw 1.5 Tsi is the hard/software trying to get below emission levels.
A bit like dieselgate.

Martyn1981

Goudy said:

I wonder why it's suggested that you don't drive it carefully or don't hang about.
I guess they don't mean drive it carelessly and speed.

Or do they mean drive it enough to get it all hot enough to start a DPF regeneration cycle and long enough for it to complete, otherwise there could be problems?

Seems a bit odd, making an efficient engine and then having to drive it otherwise to make sure it works properly. 

Only anecdotal, but about 8yrs back my father was getting a new car. I suggested he get a petrol this time (he'd been driving diesels since the mid 80's) as the savings were small, v's the higher cost, as he was no longer driving a lot, and also I was concerned about the DPF, but he didn't know about them, and went diesel anyway.

Nothing but trouble after a few months, and he was advised (and we read up) about the level of revs he needed and the length of time for a regen. As he was older and a slower driver, who preferred 60mph to 70mph, it meant he would have to drive in 4th gear, not 6th (or 5th). It sounds crazee, and would defeat his attempts at fuel saving.

In the end, they took the car back, accepting that they hadn't adequately informed him that it might not be suitable. He was quite lucky I think.

Obviously, he may have been unlucky, and perhaps the technology has advanced, but it was an eye-opener.

WellKnownSid

sevenhills said:

What did they mean by 'careful' driving, do you think they were just making excuses, did you stop driving carefully?

Driving everywhere with small throttle inputs.

It was my trained German mechanic that told me - it wasn't his car so he had no need to make an excuse.

I was told to give it an Italian tune-up (4,000 revs minimum) once a week when fully warmed up - which I have done ever since - and pre-DPF days the amount of soot that would clear out of the exhaust when I did that just highlighted that it was needed.

Goudy

It's not clearing out soot when you accelerate hard or drive in a low gear hard, it's producing more of it!

There is no air control in a diesel, no butterfly valve, no throttle body or anything like that.
To accelerate/increase rpms the injectors simply add more fuel and that increases rpm so it sucks more air in, that's it.

Yes, most have turbos that increase the amount of air, but it's the adding of more fuel that produces more exhaust gas that turns the turbo vanes to produce the boost.

Fuel when burnt creates soot, adding more fuel creates more soot, so all that is happening when you do an "Italian Tune Up" is you are creating more soot for the emissions controls to deal with.

With this in mind, driving "carefully", ie with low rpms the engine will produce less soot, less fuel burnt means less soot produced.
Also at low rpm, modern diesels will run a little leaner/hotter and at times inject no fuel at all, like on the over run.

This is great for mpg and great for soot, but when it runs like this the combustion chambers run hot (we'll come back to this in a minute) as it's just pumping air so produces more nitrogen dioxides, which is why the EGR is active at these times.
The EGR allows exhaust gas which lacks oxygen back into the combustion chambers to cool combustion which reduces the nitrogen dioxides being produced.

As I wrote earlier in this thread, the more soot the DPF traps the more it will try to regenerate.
The trouble is when they don't start a regeneration cycle because the engine management doesn't detect the correct conditions, like enough heat. (not engine temps but exhaust/filter temps)
Or 
The regeneration cycle gets interrupted by turning the engine off.

The main cause of both of these is short tripping. 
That is not allowing it to get hot enough and it's not running long enough to perform a regeneration.

As we now know, lighter throttle equals leaner running which means it runs slightly hotter so can heat the filter better.

This means they tend to reach ideal conditions for regeneration when they are ran at steady speeds for longer trips. Plus, when they do run like this they won't produce the same amount of soot as they would when stop starting and repeated accelerating/decelerating on short hop trips.
Accelerating hard tends to cause them to run richer, which produces a cooler exhaust gas and slows the heating of the filter.
 
Less soot plus ideal regeneration conditions equals happy diesel.

When this doesn't happen it can cause the problems we have all become familiar with, full filters and post injected fuel diluting engine oil and the problems that can cause.