HJ always praises the higher cost detergent added fuels. Has there been any independent tests done to prove which ones offer the best in terms of detergent efficiency and performance / mpg improvement over the standard fuel? Or what is your own experience and recommendation? Thank you ....
There's no way you can compare the 'generally', as many cars are not specifically set up to gain that much in terms of performance, for others, the cleaning ability of fuels with detergents in them aren't that great either - for example, GDI-only (especially early examples) petrol engines, where the fuel doesn't wash over the intake valves to clean them, and thus provides only a marginal cleaning effect on them.
They do apparently help keep the fuel injectors from getting gunked up and thus provides a more even, controlled spray of fuel.
I realise HJ does recommend both petrol and diesel superfuels from the branded filling stations (especially Shell) because he has had a long experience of just using them with no ill effects on any of his cars, but then neither have many of us who've essentially been using supermarket fuels for decades. Again, the useage pattern, type and age of the car/engine makes a LOT of difference.
What is telling is that, as far as I know (someone please correct me if they believe I'm worng on this), I do not recall one independent test being published to prove or otherwise the claims of the fuel producers, and even the literature I've seen from the fuel companies seems more marketing than the type of peer reviewed documents that would appear in a science journal. I get the same sort of guff from building services equipment manufacturers, but at least they have the excuse that they (in the main) don't have $Bns of cash lying around to pay a trusted independent science team to test all their (many) products - fuel companies have only a handful.
I'd like to see tests done in a similar vein to those for tyre tests, but even more rigourously. If the fuel companies know it's all on the money, then they should spend some to prove it to us. Same goes for the fuel additives firms. After all, this isn't 100+ years ago with street salesmen peddling snake-oil.
From personal experience, I found using Shell super petrol for a while in my port-injected Mazda3 (used almost exclsuively for longer trips, so likely no significant injector/valve problems to start with), I got about 3-5% (2mpg max) extra mpg on very similar hourney patterns. Not sufficient IMHO to justify the 10-12% extra price (over supermarket UL) in the fuel.
I got a similar effect by using a 4-dose bottle of Redex fuel injector cleaner, which is about 4x cheaper if you get it when it's on offer. As such, I but a bottle every year or two and that's it. Others who use their cars for mainly short urban trips from cold may find that using branded super fuels is better. With diesel, the benefits seem to vary far more in cleaning performance than for petrol engined cars, wherby the actual engine performance seems to be more of a benefit, at least to otherwise well-looked after cars.
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