This is my understanding of "Hot" and "Cold" Spark plugs:

Hot Spark plugs have less contact with the metal part of the plug. This reduces heat leaving the ceramic part and thus burn away more deposits.

Cold spark plugs let more heat leave readily, thus it runs cooler.

With this knowledge, it seems that high performance engines, or people who drive alot and heat up their engine should use Cold spark plugs.

Question:

1. What happens if you use a Hot spark plug for a performance engine - Is the worst case scenario, it will blow up the plug?

2. What happens if you use a Cold spark plug for a low performance engine - Is the worst case scenario, the car won't start? e.g. on cold winter mornings.

http://www.autospeed.com

Covers all your concerns with spark plugs, they have about 3 extremely well written documents which explains the deal with hot and cold plugs, how to tell whats happening etc.

That is the single best website on tech docs i know of

Auto speed is awesome stuff.
You know those resistors on the internet that everyone says don't work for more power,the guy at Autospeed thinks they are great and i know who i'd back in hey.

What happens when you get too much carbon (black soot) build up on your Spark plugs?

Worst case scenario?

The spark plug will foul and stop... um ... sparking. If its black than the heat range is too cold and the self cleaning properties of the plug are diminished, some times to the point where it will miss fire and inevitably the plug will soot up and become unreliable.

It could also mean though that you can have mechanical troubles such as running to rich or burning oil. But if the engine is in good mechanical condition, than a black plug is too cold.

A white almost new looking plug is running to hot and it will eventually burn out and stop working, you could also just be running lean.

If you plugs are black try the next heat range up until you get nice tan coloured plugs.

So did I do the right thing by switching over from Bosch Super Plus WR9LCX+28 to Motorcraft Denso W16EXR-U ?

Ok so the bosch plug cross referenced to an ngk is a BPR4ES-11. WAY to hot. it should be a
5 or a 6.

And the denso converts to a ngk GR45, still to hot.

Your plugs will be very white and almost brand new looking with maybe little to no tan. These will burn out and die real quick....

Oh hold on is this a e-series???

Anyway they should be very tan. Drive the car a little then do a plug chop and see what colour they are.