If it was an engine shot and looked black, it was probably CD2. It is the only stuff I have ever seen that actually cures into the plastic when used properly - leaving a very black appearance with no oily film like most.

I have used it on other parts of the car, but without the setting in heat of the engine bay, it does not last as long. I only do my bay 1-2 times a year and with a simple wipe down, it always looks like the photo below.

The only problem is that CD2 is very difficult to find, not sure if it is en eco-terrorist or if the company stopped making it. The company gunk offers an engine shine replacement that is petroleum based and no good, in my opinion. If you can find CD2, I would put it as the best out there for engine bays....