I’m running a three-month trial of Redex fuel system additives to see if I can feel any increase in my car’s performance or any measurable difference in its fuel economy.
I’m now at the halfway point of my three-month trial, and I’ve been fielding a few questions from people along the way whenever I’ve mentioned it. Mostly, “What is it?” and “What does it do?”
Different kinds of fuel additives
The particular type of fuel additives that I am trialling are cleaning agents that claim to reduce build-up on your engine’s fuel injection system., meaning that the correct amount of fuel is being injected into the important bits of the engine and not being wasted. By de-clogging the fuel system, fuel flows more freely and should improve both performance and economy.
It’s probably easiest to think of these system cleaners as a bit like drain de-clogging liquids, or de-scaling agents for your coffee machine or kettle or iron or washing machine, etc. The end result should be a sparkling clean system of tiny pipes that allow the fuel to flow more freely into the important bits of the engine, and should improve both performance and economy.
Of course, to notice any improvement, the system needs to have been clogged up to start with. A brand new engine is already clean and shiny, so a cleaning agent won’t really give you any benefit. You’re far more likely to see noticeable benefits from older, higher-mileage cars.
There are other kinds of additives that are specifically designed to improve your car’s performance by adding a bit of extra kick to the fuel. These are usually called “octane boosters”, but they’re a different thing from what we’re reviewing on this trial. They are more like vitamins or other dietary supplements. Everybody’s different in terms of their diet, their lifestyle and their own genetic makeup, so taking a daily multi-vitamin tablet may benefit one person yet have no noticeable impact on another person.
The trial process
The trial commenced by adding a 500mL bottle of Redex “5-in-1 Advanced Fuel System Cleaner”. This is a concentrated cleaning product, and is recommended as a first step and then again every few months. You simply add it to your tank before putting in your petrol.
For each subsequent fill-up, I have been adding a 90mL bottle of regular Redex “Petrol System Cleaner”. The company produces specific products for both petrol and diesel engines, so make sure you’re using the right one for your vehicle.
At every fill-up, I’ve also been recording my mileage and the amount of fuel added so I can work out the fuel consumption. This has also allowed me to compare my actual results with the number suggested by my car’s trip computer.
Obviously, this is not a laboratory trial conducted in perfect conditions using perfect scientific methods. That means there will inevitably be variations due to traffic conditions, weather, different journey types and speeds, and so on. However, I’m doing what I can to keep things consistent. My car is a 2013 Mazda MX-5, and it only ever carries me (and sometimes by toddler son if I’m doing the nursery run). Plus the boot’s tiny. That means that there’s minimal variation in weight across the course of a tank.
Unless it’s raining, the top on my car is always down when I’m driving – and we really haven’t had much rain in the last six weeks. Having the top down all the time is not great for fuel economy because it messes up the car’s aerodynamics, but at least it’s consistently down every day.
I fill up every time at the same petrol station, using regular 95-octane unleaded petrol.
My driving journeys have basically been the same for the last six weeks, which is my usually 25-mile round trip to work every day. The only variation in that has really been traffic along the way, and over the last month there has been a lot of congestion due to an HGV diversion in the next town. That’s meant a lot more big trucks and coaches on my commute, and traffic has been frankly awful for about a month. The good news is that’s finally coming to an end shortly.
Fuel economy results so far
Prior to starting my Redex trial, my fuel economy tended to hover around the 30mpg mark depending on circumstances. My car was serviced a couple of months before the trial started and only has 30,000 miles on the clock, so I haven’t had any great expectations of seeing substantial movement on my fuel consumption figures.
My first fill-up with the was then followed by a 150-mile motorway trip, although a fair bit of that was crawling around the M25. Anyhow, the first tankful saw an overall result of 34mpg; a good start, but probably affected by the motorway run.
Since then, I have filled up another three times using the small 90mL bottle of regular . My driving has purely been the daily commute, but as mentioned the traffic has been rubbish. The numbers show fuel consumption of 30, 28 and 30mpg for each tankful, so it’s much the same as I’d normally expect. Again, traffic conditions will have played a part, this time negatively influencing the result.
I filled up the car again a couple of days ago, and have also noticed that traffic is much better this week. Hopefully, that means the next tank’s results will be a bit more indicative of my usual driving circumstances.
We’re not doing any performance testing on this trial, so it’s simply been a case of me trying to detect any noticeable improvements in performance.
I think that the car has probably been running a bit smoother after using the 5-in-1 cleaner. Once or twice in recent months, I had noticed a very slight cough when accelerating hard. It was nothing really significant, only happened very occasionally and I had just put it down to a bit of gunk in the fuel. I haven’t noticed anything similar since I’ve started using Redex, so I’d say that the cleaning agents have been doing their job and keeping the fuel system running properly.
At this stage, I’d have to say I really haven’t felt that the car is performing any better. Obviously, I’m not doing any timed acceleration runs on a drag strip, but the car doesn’t feel to be performing any differently than before I started using Redex.
To be fair, this isn’t really the main point of these particular products; if I wanted to try and increase the car’s performance, I’d try the or just use premium unleaded fuel, both of which increase the octane level of the fuel for a bigger bang in the cylinders.
Incidentally, taking proper fuel consumption measurements has allowed me to compare the actual results with the on-screen information in the car’s trip computer. It seems that my Mazda is about 0.5 mpg optimistic in its read-out as every time I’ve filled up, the results have been about that much worse than the average fuel consumption readout in my dashboard. This is pretty normal for most cars, and the fuel economy numbers on the screen should only be considered a guide anyway.
The only other point of note is that the Redex bottles have a really annoying inner seal, like most bottles these days. It’s particularly difficult to remove, and usually I just end up stabbing it with my car key to puncture the seal and tear most of it off. That’s fine for my Mazda, as it still has a proper key that goes in a proper ignition barrel. Most newer cars no longer have that, however, so you’d need to have your house key or some other sharp implement handy to get the stuff out of the bottle.
I’ll be continuing to run my Redex trial for another six weeks, so I should have a final report for you by the end of August.
The review is sponsored by .