Which Fuel Additive Do I Need? The Guide for Petrol, Diesel and Classic Engines
There’s a fuel additive for almost everything: cleaning injectors, protecting against E10, replacing lead, boosting octane, reviving a blocked DPF, storing a car for the winter. The trouble is knowing which one you need. The answer depends on two things: what engine you have and what you want the additive to do. This guide gets you to the right Millers treatment quickly, then explains each one in more detail, with links to our in-depth guides.
The 30-second fuel additive picker
| Your situation | Use this | What it does |
|---|---|---|
| Classic or older petrol car or bike, built for leaded fuel | VSPe Power Plus | 3-in-1: lead replacement, E10 protection and up to 2 extra octane numbers |
| Vintage, concours or historic race engine that needs true leaded fuel | Tetra BOOST E-Guard 15 | Turns unleaded pump petrol into genuine leaded fuel |
| Modern petrol car: regular care and E10 protection | Petrol Power EcoMax | Protects against ethanol and keeps the whole fuel system clean |
| Petrol car that’s hesitating, running rough or losing power | Petrol Injector Cleaner | Maximum-strength one-shot clean of the injection system |
| Modern diesel: regular care | Diesel Power EcoMax | Keeps injectors and DPF clean and adds up to 4 cetane numbers |
| Diesel with lost power, smoke or poor economy | Diesel Injector Cleaner | Maximum-strength one-shot injector clean |
| Diesel with a DPF warning light, or lots of short trips | DPF Cleaner & Regenerator | Lowers the temperature needed to burn off trapped soot |
| Tuned, high-compression, track or classic engine that pinks or knocks | CVL Extra | Powerful octane booster to prevent knock and detonation |
| Laying a petrol car, bike or machine up for winter | Tank Safe | Protects the tank and fuel system from corrosion in storage |
| Rusty or leaking fuel tank | Slosh tank sealer kit | Not an additive: cleans, de-rusts and seals the inside of the tank |
Modern petrol engines
Modern petrol engines, especially direct-injection ones, gradually build up deposits on their injectors and in the fuel system, and today’s E5 and E10 petrol contains ethanol, which attracts moisture and can corrode fuel system parts. There are two ways to deal with it:
- Prevention: Petrol Power EcoMax. A multi-function treatment that protects against the corrosive effects of ethanol in E5 and E10, keeps injectors and the fuel system clean, and helps restore lost performance and economy. It’s dosed at 1ml per litre, so one 500ml bottle treats up to 500 litres, about ten 50-litre tanks.
- Cure: Petrol Injector Cleaner. A maximum-strength, highly concentrated one-shot treatment that removes deposits, usually in a single tank. It helps with rough running, stalling and hesitation, cuts emissions and improves economy. One 250ml bottle treats 60 litres; badly fouled systems may need a double dose.
Read more: fuel injector cleaner guide and E10 petrol problems.
Diesel engines
- Prevention: Diesel Power EcoMax. Keeps injectors and the DPF clean, adds up to 4 cetane numbers for smoother combustion, reduces smoke and emissions, and helps restore performance and economy. One 500ml bottle treats up to 500 litres.
- Cure: Diesel Injector Cleaner. A maximum-strength one-shot treatment that restores power and acceleration, cleans the injectors, reduces emissions and improves economy. One 250ml bottle treats 60 litres, and it’s safe with AdBlue systems.
- DPF problems: DPF Cleaner & Regenerator. Lowers the temperature needed to burn off trapped soot, which is ideal for short-trip, stop-start driving where the DPF struggles to regenerate. One 250ml bottle treats 60 litres; used as a preventative, that’s about every 2,000 miles (3,000km). It’s safe with AdBlue.
Read more: DPF cleaner guide and fuel injector cleaner guide.
Classic and older engines
Engines designed for leaded petrol (generally pre-1996 cars and many older bikes) can suffer valve seat recession on unleaded fuel if their valve seats aren’t hardened. They’re also more vulnerable to the ethanol in E10.
- VSPe Power Plus: the everyday choice. One dose does three jobs: lead replacement to prevent valve seat recession, protection from the corrosive, moisture-attracting effects of ethanol in E5 and E10, and an octane boost of up to 2 octane numbers (20 points). The 250ml single shot treats about 50 litres, and the 500ml multi-shot treats about ten 50-litre tanks.
- Tetra BOOST E-Guard 15: for the purist. The only additive that makes genuine leaded fuel from unleaded pump petrol, giving the full valve-seat protection of BS4040 leaded fuel. It’s specified by national motor museums, marque experts and classic race teams. The standard dose is 350ml per 40 litres (110:1), giving 97-octane “4-star” from 95-octane unleaded.
VSPe is designed for classic engines. For a modern petrol car that doesn’t need lead replacement, use Petrol Power EcoMax instead. Read more: lead replacement and E10 protection for classic cars and VSPe vs Valvemaster.
Performance and motorsport
Tuned, high-compression and competition engines, and classics with high compression ratios, can suffer knock, detonation and pinking on pump fuel. Millers CVL Extra is a powerful octane booster that lets them run cleanly and make their best power. It’s a strong dose: one 500ml bottle treats up to 20 litres for the maximum octane lift, and you can use less for a milder boost. Read more in our octane booster guide.
Storage and lay-up
Petrol left sitting in a tank over winter attracts moisture and can corrode the tank and fuel system. Millers Tank Safe gives powerful anti-corrosion and vapour-phase protection for the tank and fuel system, and keeps carburettors clean, in both carburetted and fuel-injected petrol engines. Add one 250ml bottle to about 50 litres of fuel, and temporarily block any open fuel breathers for the best protection. See our winter lay-up checklist. If the tank itself is rusty or leaking, an additive won’t fix it: see our fuel tank sealing guide.
Dose rates at a glance
| Product | Bottle | Treats |
|---|---|---|
| VSPe Power Plus | 250ml single shot / 500ml multi-shot | About 50 litres / about 10 × 50-litre tanks |
| Tetra BOOST E-Guard 15 | 945ml can | 350ml per 40 litres (standard dose) |
| Petrol Power EcoMax | 500ml | Up to 500 litres (1ml per litre) |
| Diesel Power EcoMax | 500ml | Up to 500 litres |
| Petrol Injector Cleaner | 250ml | 60 litres (one shot) |
| Diesel Injector Cleaner | 250ml | 60 litres (one shot) |
| DPF Cleaner & Regenerator | 250ml | 60 litres; about every 2,000 miles as a preventative |
| CVL Extra | 500ml | Up to 20 litres (maximum boost) |
| Tank Safe | 250ml | About 50 litres |
Getting the best from a fuel additive
- Add it before you fill up. Pouring the additive in first and then filling the tank mixes it thoroughly with the fuel.
- Use the right product for the fuel. Petrol treatments go in petrol engines and diesel treatments in diesels.
- Match the product to the engine. VSPe and Tetra BOOST are for engines that need lead replacement; modern petrol cars need EcoMax.
- Stick to the dose. More isn’t better, except where the label says a double dose can help badly fouled injectors.
- Don’t double up. Avoid combining several products that do the same job. If you’re not sure, ask us.
- Additives aren’t a repair. They clean and protect, but they won’t fix a failed injector, a damaged DPF or a mechanical fault.
Fuel additive FAQs
Which fuel additive is best for E10 petrol?
For a modern petrol car, Millers Petrol Power EcoMax protects against the corrosive effects of ethanol in E5 and E10 and keeps the fuel system clean. For a classic or older engine, VSPe Power Plus adds E10 protection plus lead replacement and an octane boost.
What is the best fuel additive for a diesel?
For regular care, Diesel Power EcoMax keeps injectors and the DPF clean and adds up to 4 cetane numbers. For a diesel that has lost power or is smoking, use Diesel Injector Cleaner, and for DPF problems or lots of short trips, use DPF Cleaner & Regenerator.
Do I need a lead replacement additive?
If your engine was designed for leaded petrol (generally pre-1996 classics and many older bikes) and doesn’t have hardened valve seats, yes, to prevent valve seat recession. VSPe Power Plus is the everyday choice; Tetra BOOST E-Guard 15 makes genuine leaded fuel for purists and historic racers.
Can I use VSPe in a modern car?
VSPe is designed for classic and older engines that need lead replacement. For a modern petrol car, Millers recommend Petrol Power EcoMax, which is formulated for modern engines and protects against E10.
Do fuel additives actually work?
The right additive for the right job does. Cleaners remove deposits that build up in injectors and the fuel system, octane boosters reduce knock, and ethanol protectors reduce corrosion. They won’t repair mechanical faults, so if a problem persists after treatment, have the engine checked.
Should I add the additive before or after filling up?
Before. Adding the additive to the tank first and then filling up mixes it thoroughly with the fuel.
In-depth fuel guides: lead replacement and E10, E10 petrol problems, VSPe vs Valvemaster, injector cleaners, DPF cleaner, octane booster and winter lay-up.
Looking for oil treatments instead? Engine Flush, Stop Leak and Driveline Flush are covered in our oil system treatments guide.
Mowers, strimmers and chainsaws? See our small engine oil and fuel guide for mix ratios, E10 fuel care and winter storage.
