There are many different fuel additives on the market, ones designed specifically for both petrol and diesel engines, but are they worth it, will you really see the benefits on both performance and your pocket?
Do they improve mileage?
Additives have been reported to improve mileage when using a standard base fuel over the more expensive diesel fuels that come pre-loaded with various additives. Additives can increase the British Thermal Unit (BTU) which could result in greater milage and performance per tank. SO if this is the case, does it work out more cost-effective to buy the additive and use the base diesel, or are you better off going for the high quality more expensive diesel that already has the additives?
The only way you can figure this out is to take the price it would cost you for a fuel tank of standard diesel compared to the performance diesel with the additives, what extra would it cost? Then look at the cost of the additive and how many tanks of diesel it would cover, split this across the tanks and add it to the base fuels price and voila, you have your price comparison. It may also be worth looking at the actual mileage you get per the standard tank with the additive added versus the performance diesel with the pre-added additives.
Cleans the engine and better for the environment?
Diesel fuel can cause the build-up of carbon deposits in various areas of the engine, especially in the diesel injectors. Additives do help reduce these deposits, allowing a better fuel flow which could help maintain the engines original fuel efficiency. The additives can help cause more complete combustion in the engine and thus help result in lower emissions, a ‘cleaner’ running vehicle.
Summary
Fuel additives in some cases may see you gain performance and MPG when using base diesel, though using the performance diesel may give you the same effect. Using a good diesel additive on an ageing engine may remove build-up of carbon deposits initially and restore some performance, but in some cases, a trip to a mechanic may be needed to solve any underlying problems.
The only way to really find out if a good quality additive will give your engine benefits is to try it and see if you get any gains, no two circumstances are ever the same.