What's the difference between diesel and premium diesel fuel?

The major difference between diesel fuel and premium diesel is, depending on the brand, a few additives designed to keep the inside of the engine clean. Is premium diesel a guarantee or promise that your diesel-powered vehicle will run better, emit fewer tailpipe emissions or use less fuel? No.

Fuel companies are notoriously tight-lipped about what additives go into their 'premium' diesel products. But the best guess is that it's a range of detergents designed to clean soot and other deposits off the inside of the engine. Which means the diesel vs premium diesel comparison is one that you don't really need to think about day-to-day. The best diesel fuel in Australia is the stuff that meets all Australian Standards and is pumped from a clean underground tank.

The real measure of a diesel fuel's quality is in its cetane number (similar to petrol's octane rating) which evaluates how ignitable the fuel is when compressed (which is how a diesel engine burns its fuel; there are no spark plugs, ignition relies on compressing the diesel-air mixture).

Beyond that, quality is judged by the amount of sulphur and other contaminants in the fuel. So does premium diesel have a better cetane rating than normal diesel? No. So is premium fuel worth it? Not if it's diesel we're talking about.

Premium diesel (or super diesel as it's also mistakenly known) is marketed under various brands, all of which suggest a major advantage (like Diesel Plus) while other brands go down the corporate brand route (Caltex Vortex, for instance, tying the product to its higher-octane petrol variant).

So, if all this is the case, you can actually make your own premium diesel brew by adding a bottle of detergent additive to your car every few tank fulls. In terms of diesel performance, you won't be missing out, and even though some of these additives aren't cheap, given the average premium diesel price of a few cents more a litre, you might even wind up in front.

So, which diesel fuel is best? The one that comes from a clean tank at the lowest possible price.