Say that a friend had been silly enough to skim the text on the bottle of fuel additive, before mixing it into a full tank of fuel for his 40'000 km kawazaki z750. And say that it turned out this additive was not so much a fuel stabiliser as a lead substitute, with a clearly typed-out warning against using it on engines equipped with a catalytic converter.

How long would you estimate it would take until the cat converter was well and truly poisoned? A few minutes? Half the tank of poisoned fuel? What should my friend expect ?

I assume, of course, that he should drain the tank regardless.

edit: link to information on the additive


Those lead substitutes aren't one class of substances. Some have metal-organic sulfur compounds in it which are bad for the cat. Some haven't. Yours seem to be alcohol/butylether mostly, which simply increases the anti-knock rating.

The latter class of substances is most common and does not hurt the cat at all.

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  • In this case, is the warning on the label ass-covering (against using the compound with a cat) or somewhat true ? If I do drain the tank, should I take extra precautions to remove whatever might be gunking up in places? – Dugas Feb 12 '18 at 7:33
  • No, you don't need extra safety measures other than for standard gasoline. – Janka Feb 12 '18 at 12:52

For future reference:

I went ahead and emailed the additive manufacturer.

They said the additive is indeed alcohol based, and the lead substitute in this case is potassium, which while it is not recommended for cat converters, should not cause serious damage over a single tank.

They recommend driving it off, and not doing it again. I might siphon the fuel anyways as an extra precaution, though.

edit: also found this study on the poisoning of catalytic converters

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  • 1
    Ah, okay, so most likely it's the potassium analogon of en.wikipedia.org/wiki/Docusate, which is synthesized for the medical purpose in high amounts and has to be only run through an ion exchanger for the use as a lead substitute. – Janka Feb 12 '18 at 12:49

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