Even the complete version of my article on diesel fuel leaves some open questions. Before you ask, here are my answers:

So which car should I buy?

If the answer were simple, I would have fit it into the article. The conundrum is this:

Diesel cars emit somewhat less carbon dioxide. (Not as much less as you thought, but less nonetheless.) But diesel cars emit more local pollutants. But the newest, clean, Euro 4 diesels driving on ultra-low-sulphur fuel emit acceptable levels of local pollutants. But half of all the ultra-low-sulphur diesel in South Africa is made in a way that emits huge amounts of carbon dioxide.

You can’t win.

You also can’t use diesel as an excuse to buy a bigger, more powerful vehicle than you need. That’s exactly what the car companies are trying to get you to do. (See question below: “Why are SUVs cleanest?”) I think that most city dwellers, especially those on the Highveld, should buy the most fuel-efficient petrol car they can find that suits their needs. If you can afford it, the Toyota Prius is ultra-clean for both local pollutants and greenhouse gases.

If you live in a rural area in the Highveld, where local air pollution from traffic is not as much of an issue, you might consider buying a diesel vehicle and running it on normal, 500 ppm sulphur diesel. You are most likely to avoid coal-based fuel that way and will reduce your contribution to global warming. (Note that if your manufacturer says you must use ultra-low-sulphur fuel, it could damage your vehicle to use 500 ppm sulphur diesel.)

If you live in KwaZulu-Natal, most of your fuel comes from petroleum. With the coal issue set aside, diesel makes more sense. Look for the vehicle—petrol or diesel—with the lowest CO2 emissions that suits your needs. In KZN cities, you should only buy a diesel if it meets Euro 3 or Euro 4 specifications and fill it with ultra-low-sulphur diesel.

Cape Town is even more complicated. Fuel retailers generally buy from the nearest refinery, but Sasol transports ultra-low-sulphur diesel all the way from Secunda to its filling stations in Cape Town. I wouldn’t buy it. BP stations get their ultra-low-sulphur diesel from the Durban refinery that BP owns with Shell. I don’t know about the others.

Does a diesel make economic sense?

The Diesel Dilemma, a report by the Union of Concerned Scientists, concludes that:

Gasoline vehicles are more cost-effective than diesel for reducing oil use and lowering global warming pollution.

By that, they mean that if the extra expense it takes to make a clean diesel engine were put toward greater efficiency in petrol vehicles, the petrol vehicles would save more oil and greenhouse gases than diesel cars. Unfortunately, other than hybrids like the Prius, few petrol cars have benefited from that kind of attention toward fuel economy.

Looking at clean diesels available in South Africa, the BMW X5 sd costs an astounding R68,000 more than its petrol equivalent the X5 si. Even after 150,000 kms, you would be R47,000 poorer, at October’s fuel prices. The diesel Honda CRV, which has perhaps the most advanced diesel engine on earth, emits 10 percent less carbon dioxide than a similar petrol CRV and costs R20,000 more. After 150,000 kms, you would be only halfway toward recouping that differential.

I’m not a great believer that every expenditure for the sake of the environment must pay for itself. If someone in Durban really needs a 4×4 soft-roader and is willing to pay the extra money for the sake of the earth, they should buy a diesel CRV. I’m just not sure how many people out there really need a 4×4 soft-roader.

Smaller diesel cars may have a smaller price differential, but few if any small diesels in South Africa today are clean enough to meet Euro 4 emissions standards. In 2008, some will be available, and perhaps they will pay for themselves over time. They certainly will make more sense for the environment than a 3-litre diesel powerhouse with a lot of emissions controls on it.

Why are diesel SUVs cleanest?

The cleanest diesel engine BMW has brought to South Africa is in its giant X5. Honda’s cleanest diesel is on the 4×4 CRV. VW’s only Euro 4 vehicle in South Africa so far is the Touareg SUV. Volvo has put its best diesel emissions controls on the 4×4 XC. What’s going on here?

I put this question to Jan Lotter, the product planning manager for BMW South Africa. He laughed, and said that I had made a good observation. Then he said:

There’s a growing awareness of SUV consumption; people are talking about carbon footprints, environmental impact. This is a little more of an investment to make them more acceptable.

I think he’s right. It’s a last-ditch effort to keep people who are starting to feel that it’s environmentally unacceptable to drive a 4×4 to Sandton City from buying a smaller, less expensive car.

Lotter made another salient comment:

The unfortunate thing about diesel is that it is still expensive. With the invention of common rail diesel technology, and going to higher and higher pressures [to make diesel engines cleaner] it becomes difficult to introduce entry-level diesels.

BMW has a small, Euro 4 diesel car that can even beat Toyota’s Prius in fuel efficiency, the 118d. But it isn’t sold in South Africa.

Does it really make a difference whether I buy coal-based fuel?

One could argue that avoiding coal-based ultra-low-sulphur diesel from Sasol’s Secunda plant does nothing for the environment. Fuel is in short supply in this country and Sasol will keep producing to capacity. The company may end up selling the fuel as regular diesel and it may end up selling the diesel somewhere else, but Secunda’s emissions are not going to decline just because fewer people buy ultra-low-sulphur diesel in the interior.

This argument has some validity, but I would make three counter-arguments:

  1. Sasol makes more profit selling their diesel as ultra-low-sulphur diesel. The more profit they make on diesel, the more likely they are to go ahead with the second coal-to-liquids plant, which is now in the feasibility-study stage. Such a plant would be a disaster for South Africa’s greenhouse gas emissions.
  2. If ultra-low-sulphur diesel becomes in short supply, the government may be more favourably inclined toward another coal-to-liquids plant.
  3. It might just bother your conscience to think that the source of all those greenhouse gas emissions killing polar bears and ruining the crops of African farmers is sloshing around in your fuel tank.

Don’t you have anything nice to say about Sasol?

Sasol does an impressive job of reporting emissions data and was willing to let some of its experts talk to me openly for this story. The refinery owned by BP and Shell, by contrast, would only answer questions by email and mostly didn’t answer questions at all. Sasol’s greenhouse gas emissions are edging down relative to their total production, partly because they are using more gas from Mozambique, which is less polluting than coal. There, I managed to say something nice about Sasol. (But if you haven’t read the M&G article yet, their Secunda plant has roughly the same greenhouse-gas emissions as Israel.)

Don’t you have anything nice to say about BMW?

I’m afraid that BMW’s marketers set themselves up for criticism by portraying a big SUV as a solution to global warming. That said, the company is working on some very interesting technologies for improving the fuel consumption of both petrol and diesel vehicles. In 2008 we may see the first BMWs that cut the engine instead of idling at a stop light and use the energy from braking to recharge the battery.