I had never heard of Cataclean until yesterday when I saw the full page advertisement in "Auto Express" The company's website contains no links to any independent tests in the USA, UK or anywhere else that have verifiedl its claims in the 20+ years it has been on sale. A full independent test by any well respected consumer organisation or motoring magazine that found the claims to be justified would be on the company's website within days... but no such endorsement exists.

One year my 17 year old Octavia just scraped thorugh the emissions test. The following year I used Cataclean and the emissions were way under - I've used it ever since.

I used to think snake oil - but to rme now it's snake oil that works

The only real test would be to have done the MOT before adding Cataclean, and then after. Otherwise you simply don't know if the Cataclean actually did anything. It could be that some change in your engine independent of the magic beans was the cause of improved emissions. Not saying it doesn't work, just that you need proper tests to verify or otherwise.

Automotive quackery.

I'm pretty sceptical about these sort of additives and very rarely use them. However a few years ago my wifes Mini was borderline on the emissions test of the MOT and I was warned the cat might need replacing for the next year. So I ran a bottle through a full tank of petrol about 3 weeks before the next MOT and the emissions dropped considerably from the previous year, I can't remember the exact figures but it was a very noticeable amount.

So I was pleased, and for the £20 or so it cost it seemed to sort the probem!

A subject that is scope for plenty of debate, personal experience will differ based on many semantics such as vehicle how often additive is used. Cataclean with a dose of high octane fuel has helped me get past the last three MOT emission tests and helped with a blocked CAT. This is on an old Ford from the late 90s with 274,000 miles on the clock

That's the problem with anecdotal evidence, accurate though it is - neither you nor we can tell whether it was the high octane fuel on it's own, the Cataclean on it's own or the combination of the two together.

If evidence exists that additives made a consistent difference to fuel consumption, performance or emissions they would be added to either the fuel or the service regime.

We have a market economy - no supermarket would fail to add additives proven to work. Motorists would vote with their feet and competitors happily advertise the deficiencies.

No car manufacturer will fail to fit a gizmo that is proven effective (unless covered by patents etc). Like the supermarket, competitors would make the deficiency very obvious.

So I can only assume those who report additives effective are:

• the exception rather than proven rule
• unconciously biasing their analysis (eg changing driving style)
• attributing improvements to additives despite other actions (eg changing spark plugs)
• trying to justify delusional behaviour (it wasn't really a waste of money!)

FWIW, I used Cataclean on a P-reg Subaru Impreza Turbo that failed the MOT emissions test. The MOT station recommended I try Cataclean, so I sourced a bottle elsewhere and it passed the emissions test. It was very pricey, but it worked for me.