Normal?? I have never seen it. The engine temperature never reaches more than 100C. That is nowhere near hot enough to melt the body plastic of a coil. One thing that is hot enough to melt the plastic is an electric arc. If the coil's insulation begins to fail arcing can occur outside of the cylinder between the coil and the cylinder head. Something that was quite common in the old days of HT leads. It was called "tracking" and was easily spotted as it would light up your engine bay at night when you lifted the hood. The solution was to replace the leads. I suggest you do that with these coils.When I replaced spark plugs last time, I noticed that two of the ignition coils have a funny-looking surface. At first I thought they were caked with greasy oil, but the uneven texture is the surface itself and is rock hard. It looks like the plastic has melted or been attacked by a chemical reaction. The spark plug tubes are fine and clean, so I struggle to figure out how this happened. The coils were in the car when I bought it in late 2019, and I have not had any functional issues with them so far.
My question is: what might cause this, and should I worry about it?
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