What is premium diesel?
Shell V-Power Diesel, BP Ultimate Diesel, Esso Synergy Diesel Supreme+: these premium products typically cost around 18p more per litre than standard diesel. They carry two main claims: a higher cetane number for smoother combustion, and additive packages for injector cleanliness. Here's the honest breakdown of when those claims translate into real-world benefit.
What is cetane number?
Cetane number is the diesel equivalent of octane rating. It measures how readily the fuel ignites under compression. Standard UK diesel is typically 51 cetane. Premium diesel products often claim 55+. A higher cetane number means quicker, smoother ignition, which can reduce the characteristic "diesel clatter" on cold starts and potentially improve combustion efficiency very marginally.
Most modern diesel engines are calibrated to perform within the normal cetane range. The benefit of higher cetane is most noticeable in older diesel engines and in cold weather, where better ignition quality reduces startup roughness.
The injector additive claim
All premium diesel products contain proprietary additive packages designed to clean fuel injectors and prevent deposit build-up. Modern common-rail diesel engines operate at very high injection pressures (up to 2,000 bar) and are sensitive to injector deposits. The additives in premium fuels can help maintain injector spray patterns over time.
Independent tests have shown measurable injector cleaning benefits from regular use of premium diesel, but the gains are long-term and gradual. Switching to premium diesel for one or two fill-ups is unlikely to produce a noticeable difference. The benefit is in consistent use over thousands of miles.
If you regularly cover 20,000+ miles per year in a diesel, a periodic tank of premium diesel every few months may help maintain injector health, particularly if your car has had any injector issues. For low-mileage drivers, the benefit is minimal.
The verdict by driver type
| Driver type | Benefit from premium diesel | Worth the premium? |
|---|---|---|
| High-mileage (20k+ miles/yr) | Injector maintenance over time | Occasionally useful |
| Older diesel engine | Cetane benefit on cold starts | Marginally useful |
| Modern common-rail diesel | Minimal at standard mileage | Unlikely |
| Low-mileage / short runs | Negligible | No |
| Vehicle with injector deposits | Can help clean gradually | Periodically yes |
If injector cleanliness is a concern, a bottle of fuel system cleaner additive (£5–£10, available at Halfords or Amazon) added periodically to standard diesel is a cost-effective alternative to paying an 18p/litre premium on every fill-up.