Spark plugs

[dilligaf]

Are they easier to unscrew from a hot engine or a cold one ?
And would it be different on a cast iron head than an ally one?
I have replaced plugs many times but never considered this before.

[wiltshirlass]

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[djaychela]

Aluminium expands faster than steel, so I'd guess they'd be easier to undo in a hot engine, although there would also be more chance of stripping the threads as a result of that.

Iron expands more slowly than steel, so the converse would be true with an iron head - easier to get out when cold, etc.