when removing the valve covers on some subarus, ..it doesn't matter if it is an '86 or 2000, carbed or turbo, everything under the valve cover has a light to dark color which can not be removed..is this because the oil has stayed in to long or from over heating or just poor quality motor oil...I am asking this question because my own 3 subi cars have ( 2 that are high mileage drivers) "not" exhibited the color and remain very clean under the valve covers

It most likely oil "coking" from getting hot and coming in contact with the metal surfaces. Nothing to worry about cause it happens to any type of vehicle you will ever work on.

It most likely oil "coking" from getting hot and coming in contact with the metal surfaces.

 

Quality oil does not "coke" (at least it doesn't here).

The color is produced by deposits from motor oil over time. It could be from 'poor' quality oil, or from not changing 'often enough,' from an engine running too-high oil temps, or just from the specific components of the oil.

 

Frequently, one cannot prevent this discoloration because it's a 'feature' of the engine in question. However, you could probably prevent it in most engines by changing the oil every 500-1000 miles regardless of usage. The thing is, the coloration itself does not indicate a problem so long as you're talking about a fairly light general coloring. It can also be essentially impossible to remove without mechanical scrubbing or even grinding.