What DPF additives do
Fuel-tank additives sold for DPF cleaning contain catalytic compounds (usually cerium or iron based) that lower the temperature at which soot will oxidise in the filter. Normally a passive regeneration needs ~500°C exhaust temperature; with additive it drops to 350-400°C. This makes regeneration more likely during routine driving.
When additives help
- Early warning light, soot load below ~40%
- Mostly urban driving with occasional motorway runs
- No mechanical damage to the filter or engine
- Used preventatively — every 5,000-10,000 miles
When additives do NOT help
- Steady warning light or limp mode (soot load too high)
- Ash overload (additives cannot remove ash, only soot)
- Damaged substrate
- Underlying engine fault dumping excess soot
Are factory-fitted additive systems different?
Some Peugeot/Citroen DV6 diesels and certain Ford and Volvo engines came factory-fitted with an Eolys additive system that automatically doses cerium into the fuel from a separate tank. These systems use a more aggressive additive than off-the-shelf bottles and are part of the factory regen strategy. The Eolys fluid needs topping up periodically (typically every 60,000-120,000 miles).
Best products on the UK market
Pick by additive chemistry rather than brand marketing. Cerium-based products tend to be more aggressive; iron-based products are milder. Use a product that explicitly lists DPF regeneration support, not general fuel system cleaners.
Bottom line
Additives are a preventative tool, not a fix for a fully blocked DPF. Combine with a regular 20-minute motorway run every 500-1,000 miles to keep your DPF happy. If the light is on already, head straight for a forced regen or workshop clean.