Fork plungers discoloring (yellowing)

[georgesgiralt]

Hello,
Patient is my trusted 1982 R65 European version.
The front fork plunger are yellowing (as do steel when heated) just above the seal. The discoloration is quite identical on both sides, and cover an area about 3 fingers wide. present in the front and covering 2 third of the perimeter of the plunger.
I wonder what is causing this and if it is ominous ?
And while we are at it, what fork oil (weight and brand) do you recommend ? Because I've finished the BMW oil i bought years ago from a long gone dealer....
Many thanks in advance for your help !

[Barry]

Georges,

If you mean the chrome stanchions and bearing in mind there would be more wear at the front than the rear, I wonder if it's the chrome wearing through the plating.  I don't see anyway the stanchions would get hot enough to display temper colouring.

Fork oil viscosity is a confusing subject.  I buy on the basis of the viscosity at 40 Deg C being 18- 22 cSt which will typically be marketed as a 5W.  Last one I bought was Silkolene 5W

[georgesgiralt]

Thank you Barry,
I've taken some picts but they are so bad one can't see anything. I4ll try tomorrow in the sun hoping the problem will show more.
Today, I ride the bike for about one hour and the two tubes where hot. I could hold them so, not that hot, but....
I will drain the oil and see what comes with it. Maybe some little fish ? Who knows ?
Thanks again !