First things first, let me make it clear, I am not anti diesel cars. My current car is a diesel and I’ve owned far more diesel cars than petrol. If anything I prefer them – in the UK at least, due to the high mileage I typically drive and the mid range power delivery.
So, I’ve really thought about it when I say I would never buy a diesel car to use in Malta (or any other small island for that matter). Never, ever. The reason for this statement? Diesel Particulate Filters.
Since 2009, DPFs (Diesel Particulate Filters) have been a mandatory requirement on all diesel engined cars to help them meet Euro 5 exhaust emissions standards.
Diesels produce lots of soot (particulate matter) that can cause respiratory problems and contribute to the risk of cardiovascular diseases. The purpose of the DPF is to filter and trap this soot and prevent it entering the atmosphere.
Sounds good right? So why do I have a problem with it?
I don’t. Not with the DPF itself. I can see the reason it’s been fitted and I’m all for it – I don’t want to cause anybody to have respiratory problems. What I do have a problem with, is owning a car that contains a DPF when you live on a small island. Let me explain.
The DPF traps soot/particulates and stops them escaping, right? So eventually, this soot is going to build up and need to be cleared. How does the system do that? By burning it off and turning it into harmless ash during times of high exhaust temperature in a process called regeneration.
The most common type of regeneration is ‘passive’. This relies on the vehicle exhaust reaching a high temperature – around 500 degrees Celsius – during the process of a regular journey. Generally, this means driving at a high speed (over 40mph) on a highway or motorway, for several minutes. To fully clear the system, this needs to happen on a regular enough basis to ensure that more soot is burnt off, than accumulated.
Are you beginning to see the problem?
If you don’t travel very far in your car because you live in an urban area or a small island, you’re not going to reach the required temperature to initiate passive regeneration.
Diesels are designed and made for people who do long journeys. Not people who nip to and from the shops, or drop the kids off to school. They’re more expensive to buy and diesel costs more than unleaded fuel. So you have to do a lot of mileage to feel the economic benefit of better fuel economy.
They’re also not designed for people who sit in traffic. Because whilst your journey to work may take you 45 minutes each way, if that’s mostly stop/start at low speeds, that’s not going to help you either.
There has to be some kind of backup right?
Surely the engineers have installed some kind of measure to help you out here? Yes they have. Sort of.
If you don’t drive at speed often or long enough, the engine should try to clear the DPF via ‘active regeneration’. This is where the engine lets the exhaust gases get hot enough to burn off the soot without requiring the car to be run at speed.
The engine control software senses that the filter’s getting blocked and injects extra fuel into the engine to raise the exhaust temperature and trigger regeneration. Active regeneration will be initiated every 300 miles or so depending on how you use your car and should take 5 to 10 minutes to complete.
But this only works if your car is moving. And moving for long enough for the regeneration process to complete. It’s a problem if your journey’s too short and the regeneration process doesn’t finish.
So what happens when neither passive or active regeneration has cleared the soot? Firstly you’ll get a warning light – normally amber – or engine management message if you have a more sophisticated onboard computer system. See this and you’ll need to get the DPF to regenerate itself by driving over 40mph for around 10 minutes. This is clearly not possible if you live in Malta or any other small island.
What next? Normally it’s a flashing – or red – warning light and a trip to a garage for a ‘forced regeneration’. Your car will be hooked up to a diagnostic computer and forced into regenerating itself (essentially, extra fuel is forced into the system creating greater combustion and a higher operating temperature). If this works, expect to fork out for it. Not only will you have to pay for the regeneration, your vehicle will also require engine oil and oil filter changes afterwards (the extra fuel that is added after the combustion cycle works its way into the sump and dilutes the oil).
Mostly though, it won’t work. When you’ve reached this stage it’s often too late. You’ll need a new DPF. Which is expensive. Trust me. I’ve been there.
A couple of years ago I bought a 2010 diesel Volvo. At the time of purchase the car had average mileage for its age; and knowing that I was going to be doing well above average mileage, I wasn’t concerned about the DPF. I figured my regular motorway journeys would keep the system soot free. They didn’t.
After 18 months or so, my engine management light came on, I was unable to force regen and soon found myself at a garage being quoted over £3,000 for the fitting of a new DPF and exhaust system (the DPF was so blocked it had caused damage to the pipes around it).
So despite the fact that I drove on a motorway for over 10 minutes, twice a day, and almost twice a month I did a 400 mile round trip journey on motorways, I had been unable to regenerate the DPF. Either the DPF had been completely filled by the previous owner thanks to continual short journeys, or there was a fault in the system that had prevented active regeneration.
Whatever the cause of the build up, neither passive nor active regeneration worked for me to clear it. And I was doing everything that is supposed to work. So what chance do you have on a small island with no motorways?
So it is because of all of the above that I will never buy a diesel car to use in Malta. And neither should you.