The original seems fair enough to me. Are you insisting that the entire car is melted into a puddle before the title can leave the 'parts' bit out?

That depends. What does the title say, if it's intended to convey facts?

It's correct to use that terminology even when an object is only partially melted, as in this case.

No, it is not correct. It exaggerates the facts. A journalist at a conscientious periodical wouldn't get away with it.

By adding "parts" to the submission title, at least we're still talking about a subset of the car.

Can't say the same for "rumor."

That depends on whether the rumor is a subset of the truth. Sometimes true, sometimes not.

Truth: Joe Smith has never beaten his wife.

Rumor: Joe Smith no longer beats his wife.

There's some truth in the rumor, but no rumor in the truth.