I mentioned in my last report that I’d previously noticed a slight cough or misfire from the Mazda on a couple of occasionsprior to using the Redex products, but hadn’t noticed anything since using the fuel system cleaners. I can report that the engine has still been running cleanly over the last six weeks, so the stuff appears to be doing its job in that respect. Summary

I’ve just finished a three-month trial of Redex fuel system additives in my Mazda MX-5 to see if I could feel any increase in my car’s performance or measure any significant difference in its fuel economy. H226 - Flammable liquid and vapourH412 Harmful to aquatic life with long lasting effects.H304 May be fatal if swallowed and enters airways.H336 May cause drowsiness or dizziness.Also, if your tank is larger or smaller than 50 litres you can still use the recommended dosage with same level of performance being achieved. The second week of our test actually saw the mpg deteriorate by 1.5 mpg from the pre-test week, but it’s been a steady improvement since then and we look to be getting about 3mpg more than we did before. It’s not huge – about 6-7 per cent – but we’ll take it. Strike two. How much does it cost to use Redex? As I outlined in previous reports, the type of fuel additive that I’ve been using is a fuel system cleaner rather than an octanebooster. The goal isn’t to turn regular unleaded into premium unleaded by increasing the car’s octane number, but simplyto give all the tiny pipes and injectors a thorough clean so they can do their thing without being clogged up. There has been no noticeable difference in performance, and I suspect you’d need a laboratory to really show any improvement. In the variable nature of the real world, and in a well-maintained modern car, I couldn’t detect any difference.

It’s also a really easy to use product, just putting a single bottle of Redex cleaner in to the tank at each full-up, which soon becomes second nature. What have we found in the last few months of using Redex?

Over about 2,000 miles of mainly commuting in three months, my average fuel consumption using the Redex fuel system cleaners was 31.1mpg. My driving circumstances in that time have been a pretty representative example of my usual activities, so superficially it looks like a 1mpg improvement since using Redex. Since May, I’ve been recording my fuel economy every time I fill up the tank – manually noting down the litres added and mileage covered, rather than relying on the car’s trip computer – and adding a dose of Redex to the tank.

Firstly, if you have an older or higher-mileage car, you are far more likely to see noticeable improvements in performance and fuel economy compared to a newer, lower-mileage vehicle. Given that fuel deposits and debris build up in your engine over time, it makes sense that you’ll notice a greater improvement in an older engine that has seen a few million more fuel explosions than a newer engine. If I’d been running the same test on an older car I am sure I would have seen some more noticeable results, but unfortunately I don’t have an older car to call upon for such a purpose (and buying an old banger to drive for three months didn’t really appeal!) It’s a valid question as you’re shoving additives in to your fuel tank, but the fact is that Redex have been delivering their products for almost 100 years, and are happy to declare that “Redex products will never cause any damage or impairment to your car”, and will do nothing more than provide a “reliable engine-cleaning solution” for users. Which is reassuring.We had no hesitation in trying this out, especially as just about everyone at Cars UK Towers has used Redex at one time or another, and were confident it was safe to use. After the initial 500mL dose of Redex Advanced 5-in-1 system cleaner, I have been adding a small 90mL bottle of Redex petrol system cleaner every time I have filled up my fuel tank for three months. In my situation, I don’t think I really need to keep using the additives at that rate in my car. I am likely to add a 90mL bottle every month or so and probably use the concentrated cleaner every six months to keep the Mazda’s fuel system sparkling clean. If I had an older car (or when this one starts getting older and higher-mileage), I’d keep using it every tank or at least every other tank. Given that your engine creates dozens of explosions every single second, there’s a lot of combustion going on under your bonnet. With any burning of fuel, there will be deposits and debris that forms. Sometimes it’s obvious, like the ash that forms when you burn a log in a fireplace. Other times, like in your car’s engine, these deposits are microscopic, but the principle is the same. Over time, these deposits build up and affect your ability to keep burning the fuel properly.

Yes, we will. But, to be honest, we’ll probably be misers and drop down to using it every other fill-up (which will make it cost just 2.5p per litre of diesel) and see if we notice the C-Max starting to use a bit more fuel, or be less happy when cold. The recent cold snap is what convinced our one dissenting voice, as she found the C-Max far less ‘chuggy’ on first start on cold mornings. So strike one for Redex. Has economy improved? But as 5p a litre is about half the extra of ‘Premium’ fuel, it’s pretty cost-effective as a way of getting your fuel system to work more effectively. Strike three. Will we carry on using Redex?

My fuel economy figures haven’t shown any changes that could really be attributed to the Redex products. The variation of 3-4mpg above or below the average based on driving conditions and traffic outweighs any potential gain from the products. Again, if you were running a laboratory experiment that directly measured fuel consumption and removed all other variables then you may be able to show an improvement, but it’s nothing really noticeable. Our Redex experts or ‘RedExperts’ were recently asked “what is the mix ratio for Redex?”– the mix ratio for Redex is 1 shot per 50 litres of fuel, which equates to 2.5ml per litre of fuel. Take a look at our video.