Ferrocene plug fouling - cause for concern?

[Dr Mike Oxgreen]

I’ve just changed the plugs on my Saab 9-5 Aero, and was surprised by the colour of the old ones.

Traditionally one hopes to see a tan colour on the electrodes and ceramic, but they came out with a distinctive plum red colour…



A little bit of reading (and consulting my father-in-law) yields that this is ferrocene fouling. The image on this NGK web site matches the colour exactly…

https://ngk-sparkplugs.co.th/product-knowledge/fir...

I almost always use super unleaded, frequently from Sainsbury’s. Do they add ferrocene? Also, I notice that the servicing invoice from my local independent garage lists “injector cleaner”… could it be that?

So is this cause for concern? I read that it can cause misfiring, and I suspect it may now be idling a fraction smoother, not that it was too bad before. I changed the plugs because I had no record of them having been done; they’re platinum-tipped on a 30,000 mile interval so easily overlooked.

Edited by Dr Mike Oxgreen on Friday 5th May 12:14

[Dr Mike Oxgreen]

Now I come to think of it, I *did* use an octane booster for a short while, a long time ago when fuel prices were at their most eye-watering, I started using regular unleaded but with an octane booster to save money. And even though that was at least a year ago, it says that ferrocene doesn’t burn off like other deposits do. So I suspect that might be it. Alas I don’t still have the bottle so can’t research whether that additive contains ferrocene.

[jeremyh1]

I avoid supermarket fuel
In fact I avoid supermarkets completely.
Put new plugs in and run it on v power for a while