Just pulled the valve covers off of the old 4.8 that came in my truck and noticed the rocker arms on the passenger side are much darker in color than the drivers side. What would cause this? It's an 03 bone stock ~100k miles

 

I have seen this before. One bank was running hotter than the other due to a clogged cat.

 

Weird, i usually see that the drivers side is darker.

 

My truck was the same way. Don't remember though if it was the drivers or passengers side... also the side with dark coating on everything also had lots of sludge on the valve covers.

Why I have no idea, I bought the truck with 86k on it.

 

Perhaps related to the dirty side of the PCV system vs the clean?

 

that's what i attribute it to...but the dirty side of the PCV system is on the drivers side. fresh air from the passenger side valve cover, goes through crank case, engine vacuum pulls fumes/moisture through drivers side manifold and then goes through PCV and dumped into intake and out the exhaust it goes.

i wonder if someone had the rockers off of the engine at some point in its life and switched them over to even up the wear. that's something i would do...

or check to make sure that everything in your PCV system is operational. passenger side has always been cleanest in my experience.