Does Cataclean work

Posted on January 14th, 2015 by Rob Marshall

CatacleanI find it a little unfair that many onlookers dismiss all oil and fuel additives as ‘snake oil’. While it is true that some of them offer solely a placebo affect (and may also be damaging), certain additives perform very beneficially. Therefore, I always try to maintain an open mind.

Earlier this year, I spent a lot of time researching diesel particulate filters and one of the companies that claims that its fuel additive reduces both emissions and repair bills is Cataclean. However, its fuel additive is promoted mainly as a product that cleanses catalytic converters, claims that have fallen foul of several advertising regulators, both here and abroad (see here). Yet, it was Cataclean’s Corporate Development Director’s confident assertion that interested me most of all, which was, when used quarterly, Cataclean can cut diesel soot emissions by up to 60%, helping prevent the Diesel Particulate Filter (DPF) from breaking” .

The claim is astonishing and, although DPFs do not ‘break’, they do clog. I was compelled to investigate the assertion. The company representatives that I spoke with were certain that I would notice a difference by dosing a bottle of additive to a quarter of a tank of fuel and simply allowing the car to idle on my driveway for 15 minutes, even though the instructions recommend going for a drive of between 10-15 miles, prior to refuelling.


So, the stage was set to test the claims of, potentially, a truly remarkable product, although, this was never intended to be a laboratory test, but a real-world alternative. The diesel vehicle in question was of average age and mileage for a UK vehicle (around seven years’ old with 75,000 recorded), in good mechanical health and run on Shell V-Power premium diesel for several thousand miles. It was fitted with a DPF and the main dealer diagnostic software was used to monitor the various parameters, as the engine was running.

To work in the additive’s favour, the car was driven first, to allow both the oil and coolant to reach their normal operating temperatures and the fuel level was allowed to drop, between 1/4 and empty, before a full bottle of Cataclean was added. As the tested car was fitted with standard equipment that permitted the soot loading, within the DPF, to burn away naturally, at temperatures over 400 degrees Celsius, the aim was to keep the exhaust temperatures below 300 degrees, so that any reduction in particulates could be attributed to Cataclean alone and not the natural effect that vaporizes the soot at higher temperatures.

The first test saw the car idling at between 750 and 1200rpm for 20-minutes, with both DPF soot levels and exhaust gas temperatures being monitored in real-time. The second test involved driving the car for twelve miles on an open road, non-stop, at speeds between 10 and 45mph, (at between 1,200 and 2,500 rpm) with the diagnostic equipment still assessing those parameters. These lower road speeds were chosen, so that the car would not try to ‘regenerate’, which would heat up the exhaust system and remove the soot automatically, which would ruin the experiment. All tests were performed on a warm autumn afternoon, at ambient temperatures of around 15 degrees Celsius.


After almost fifteen minutes of idling, no reduction in DPF soot loading was noticed. Shortly after, until the end of the test, the soot loading increased by almost 1.2%. During the second assessment, while the vehicle was driven, the soot load increased by a further 3.1%. The full results are below:


Vehicle not moving – idle speed average between 760rpm and 1,200rpm for 20 minutes.

Time (minutes) Exhaust gas temperature (Celsius) DPF soot loading (%)
0 – Cataclean added to fuel tank 108 37.65
10 124 37.65
14 165 37.65
18 169 38.82
20 149 38.82



Vehicle driven for 12 miles at speeds between 10-45mph, between 1,200 & 2500rpm.

Mileage Exhaust gas temperature (Celsius) DPF soot loading (%)
0 149 38.82
3 210 40.00
5 265 40.00
8 213 41.96
10 235 41.96
12 212 41.96



We were disappointed that Cataclean failed to show any soot emissions reduction in our DPF and recorded an increase. It is possible that our results could be explained by Cataclean cleaning soot from the oxidising catalytic converter, which then passed down the exhaust and into the DPF. However, if that were the case (and I have no proof about it being so), then the statement about Cataclean reducing soot levels and enhancing DPF reliability remains questionable, when the results of our tests are considered.

We presented our findings to Cataclean, the resulting full statement from which is at the bottom of this blog. All I can add further is that I would need concrete evidence that Cataclean reduces soot in a DPF, beyond anecdotal claims and analysis that is funded by the maker, before I invest my own money in a bottle. It was decided not to extend the tests further, before refuelling, because the chosen methodology ran the tests for longer, at a low fuel level, than the consumer instructions the bottle indicated, when both time and mileage are considered.

“Dear Mr Marshall,

Further to…the testing you did in relation to Cataclean and its capability of reducing the soot load in a Diesel Particulate Filter (DPF). The results were conclusive in that under the methodology you used Cataclean did not reduce the soot load in the DPF.  This is disappointing as we have so many instances from motorists and auto technicians that strongly indicate Cataclean does reduce the soot load in a DPF.  We would be happy to collate a substantial collection of these instances for you, on request.

 In order to establish Cataclean’s performance beyond anecdotal evidence Cataclean is testing the product using CEC* testing standards at a recognised UK testing facility. The aim of the testing is to establish exactly what Cataclean’s cleaning capability are and where those cleaning capabilities take place in an internal combustion engine and exhaust system. It is hoped, subject to the facility’s availability and schedule, that these results will be published before the end of 2014.

 Finally although we respect and consider your findings correct, we should like to make an observation in terms of your methodology.  In our view, a repeat of test 1 after test 2 would have been useful. We understand that this was not possible as shortly after test 2 the car went on a longer run and performed a regeneration on the DPF. ”