Egads! What Happened to my spark plug?

If I had time I’d post a picture.

I pulled my plugs today to check them b/c my car was running rough (this is actually an ongoing saga that I have posted about before but thought I had cleared up until yesteday).

These plugs are all of 2 weeks old (Bosch platinum +. On one of them the ground electrode was bent over nearly touching the center - it was NOT like that when I put it in. (No wonder it was running rough). The other 3 were perfectly fine.

I can think of a few things that would cause that - but none of them involve the car still running afterwards. What would bend the electrode like that?

The plug did take some heat - but the signs of heat are on the end near the threads - not on the electrode tab itself.

picture is worth a REAL answer, anything less well ,dunnno. kind of like me telling you what my lungs look like with words, so I cant help, sorry.


I don’t know the history but one possibility is a foriegn object. A chunk off a prior plug or a carbon chunk that broke loose are two possibilities. A boroscope would be helpful but failing that I might just leave the plug out and cover the area with a rag in an attempt to catch anything that might come out while cranking it over.

Can you see any impact marks on the ground strap?

There is no noticeable impact mark on the ground strap.

After some Googling, I’m going to guess, as you suggest, a chunk of carbon. I never would have thought that the plug electrode would give first, but apparently that does happen. Its unlikely to be anything else - I’ve never lost a chunk of plug down there and if I dropped a valve seat or something I can’t imagine anything would have survived.

I’d love to have a boroscope, but I don’t think it will ever be in the budget. I may crank w/out the plug to see if anything pops out though - thanx for that suggestion.

The center electrode is the positive and the bent electrode is the ground. Those plugs are notorious for dropping the positve electrode, especially if the gap was opened with a feeler gauge.

Are you saying the threads on the plugs are protruding into the cylinders? Correct plugs, including protrusion?
Maybe the plug tip was running so hot that excess heat curled the electrode up much like a metal wire will distort in a flame.

As far as I can tell the plugs are correct and shouldn’t be protruding - they’re the same size to the tip as the plugs I replaced, and those the same as the ones before that…and before that…And the part number came out the auto parts store computer.

I wondered about the heat but the groundstrap just has that typical “healthy” tannish-gray appearance - it doesn’t show any signs of heat stress.