Funny Car/Top Fuel engines do not discolor. Aluminum Model T or A or Flat V8 heads do not discolor. GM's Saturn all aluminum blocks and heads (Poris casting) never discolored even after 200,000 miles. Now the inside does from the hot oil baking to the surface. That color is a dark brown. On cars, the early engines leak - a lot, because of the gaskets not sealing well. Also in the early days performance/race engines used a castrol oil. That stuff will make anything leak. If an early engine (I going off early Ford conversions) has overhead valves - they spit oil all over. Giving the engine on back a good coat of oil. Early engine the compustion camber, I should say the piston rings do not seal like todays engines. This causes carbon to get into the oil system dirting it pretty quick. Sharkmouth is right aircarft engines are looked after more than new born babies. Or another way to think about it is they are like F1 cars.
After welding aluminum the surface around the weld turns white next to the weld and black/brown on the out edges of the heat pattern. The weld itself is shiny. The white, black and or brown color wipes right off with your fingers. The only time I have ever seen aluminum discolor from heat is during welding and it turns a whitish silver.
After I put all this down, it comes to me. If your car is made after 1995 it should be just plastic and aluminum. (unless you have a Ford, GM or Dodge Pickup) So pop the hood and see how it looks.
Hope I helped a little for you. If you want to model an aluminum engine failure I can tell you how that looks.
