When you're at the filling station, fuel additives may not be the number one thing on your mind. But whether it's diesel engine cleaner or otherwise, they can make a soothing difference to your engine after some miles. They may even help your car pass an MOT, depending on the situation.
Over time, during the combustion process inside an engine, there will be excess dirt in the form of carbon deposits. Once an engine builds up miles, carbon deposits could potentially harm vital components of an engine. These range from EGR valves to diesel injectorsand even the catalytic converters. Keeping them clean therefore, helps to prolong the life of your engine and act as preventative maintenance. But whereas a set of injectors plus garage labour is expensive, additives simply aren't.
There are even additives that help treat against the effects of E10 fuel. Say you're driving to the Nürburgring and you come up to a fuel station which only sells E10, you can carry a bottle of additive to ease your concerns when filling an older car.
The best at a glance:
Editor's pick: STP 5-in-1 Engine Cleaner - buy from Amazon.
Best for classic cars: Carlube Lead Substitute - buy from Amazon.
Best value: Redex Fuel System Cleaner - buy from Amazon.
Whether it's a bottle of petrol system cleaner or diesel injector cleaner, there is always a good additive for you. But as there's so many to choose from, we've made things easier by listing our top favourites and helping you go from there.
The best fuel additives
Editor's pick
Via STPSTP's 5-in-1 Ultra Engine Cleaners are available in either petrol or diesel form. They are some of the best engine cleaners on the market and simultaneously, they help reduce oxidisation, restore a bit of engine performance, clean up the injectors, and save a tad of fuel.
You're recommended to use it in a full tank of fuel every 400 miles and if you don't fancy spending all the money, STP also offer single-purpose cleaners as well.
Pros
- Very comprehensive engine cleaning product
- Versions available for both fuel types
Cons
- 400ml isn't as generous as others
The best value fuel additive
The best-value fuel additive of the lot goes to Redex's fuel system cleaner. Designed to be used in every tank of petrol, there are no specific instructions to get your head around. You can have it in either 250 or 500ml form and versions that suit either petrol or diesel engines.
It cleans up your injectors and clears carbon deposits to help your engine run cleanly and smoothly. I've been religiously using it to run my Mercedes W123, and I simply won't fill a tank without it. Even at 140,000 miles, it ticks over like a Swiss watch.
Pros
- Great value
- Really effective at cleaning your engine components
Cons
- It lacks in strength compared to others
The best fuel additive for improving fuel economy
Via Wynn'sWynn's Formula Gold fuel additives are designed with better performance and fuel economy in mind. It's a bit stronger than the Redex additive and is recommended for use in every third tank of fuel.
Both petrol and diesel versions are available, and it helps reduce carbon monoxide as well as cleaning up deposits in the fuel injection system - all contributing to less harmful gases and better engine performance.
Pros
- Great at gaining a bit of fuel economy
- Reduces harmful gases
Cons
- Redex 500ml cleaner is better value
The best fuel additive for treating E10
E10. There's a lot of noise about how it could perish fuel lines and cause damage to a petrol engine. The effect will obviously differ, depending on whether your engine was designed to run on E10 in the first place.
Nevertheless, if you're religious to E5 and one day, you have no choice but to fill up with E10, Lucas have the answer for you. This fuel conditioner is designed to limit the effects of the higher ethanol rate in E10 and above. 30ml treats 19 litres of fuel and you handily get 473ml in the whole bottle. Great for European road trips.
Pros
- Useful for E10 fuel
- Great value for usage
Cons
- Measurements on side of the bottle aren't that clear
The best fuel additive for cleaning the full system
Via Cataclean
For the best result, Cataclean recommends you use 500ml per 15 litres of fuel every three months. That is very specific compared to the rest of the products featured, but it's designed to tackle a whole eight components in a fuel system. The best bit? There are versions available for petrol, diesel and even hybrid powertrains.
These are the fuel tank and lines, injectors, combustion chambers, valves, oxygen sensors, EGR valves, cat converters, and DPF/PPF filters. It's quite a bit stronger than the rest of the products, but if your engine is suffering from internal dirt, this could be the solution to curing those issues and possibly getting a car through its MOT.
Pros
- Incredibly comprehensive engine cleaner
- Can be bought in packs
Cons
- Quite specific use instructions
The best fuel additive for classic cars
Via CarlubeAs you can probably tell by the faded image of the Aston Martin DB2 on the label, Carlube's Lead Substitute is designed to help as an additive towards unleaded fuel running in classic cars.
Leaded fuel was slowly phased out by the late 1980s in favour of unleaded. Lots of engines at the time were designed to take unleaded petrol, but quite a lot from previous generations were used to the leaded stuff. In comes the Lead Substitute, which helps reduce valve and injector deposits, cleans up the fuel system including the carburettors, and prevents oxidisation.
Pros
- Useful additive for classic car owners
- Helps an old engine run smoothly
Cons
- 300ml isn't the most generous
The best fuel additive for diesels
Via Wynn'sIf you're running a modern diesel engine, chances are it's also turbocharged. Over time, turbos can become blocked by deposits and this can lead to a lack in performance.
Happily though, Wynn's produces a number of fuel additives that target particular components and helps clean them. The Turbo cleaner is just one of them, and as well as clearing blocked turbos, it also has a hand in cleaning the EGR valves - which can also get badly clogged with soot.
Pros
- Helps remove deposits of unburned fuel particles and oil
- Restores lost power
Cons
- It isn't that comprehensive compared to other additives
Things to remember about fuel additives
Firstly, additives are used to assist in the effectiveness of your engine's combustion. Despite what labels advertise, they're not miracle workers that can add an extra 5mpg. When an engine gets dirty with carbon deposits and build-ups, its performance becomes less effective.
Fuel additives help clean up this stuff and simply restore a bit of power without the need to take a car to a garage. That is assuming it's not in need of major work. A car with faulty injectors, for example, will probably need a brand new set. With that said, though, fuel additives are a very cost-effective and easy method of preventative maintenance. If you get into the habit of using additives when you fill your tank of petrol or diesel, you can prolong the life of vital engine components. As a result, your engine will thank you.
EGR valves can get easily clogged up with dirt as well. If left untreated, you can risk a lumpy engine feel, so getting into the habit of using fuel additives can prevent these headaches.
Aaron Hussain is a commercial content writer at Bauer Media writing for Parkers and CAR. He is obsessed with classic cars and anything with a fascinating story to tell.