Darker varnish spot on rocker arm

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Jan 23, 2014
Hi guys,

I have a Mitsubishi 6G75 engine with 108,000 miles.

I just took the rocker cover off and it is very clean underneath with minimal varnish, except one rocker arm over a single exhaust valve is darker with varnish than everything else.

I assume this suggests that this rocker arm gets hotter than the rest?
What could be causing this?

There are hydraulic lash adjusters between the rocker arm and valve - I was thinking perhaps it is a bit blocked and is getting less oil flow?
It could also be that particular part is closest to a PCV opening in the cover. Look at the inside of the cover, there may be be a splash plate with an opening somewhere or holes to draw the vapors off, the part(s) closest to it are going to get darker.
Yes it is the rocker arm closest to the PCV.
Though it is darker on the side which isn't facing the PCV but I guess the same effect is true
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