Soot in the overflow tank? Is this possible?

[RobFish]

Hopefully someone can shed some light on this mystery. Over the holiday weekend I did a motorcycle trackday at Willow Springs here in So Cal. So I was prepping the truck to tow the toyhauler, increasing tire pressure and checking fluids, etc. and I noticed a dark shadow inside the radiator overflow tank. The truck has a tendency to blow a little coolant now and then but nothing too crazy. So I decide to reach my finger in the tank and see what this darkness is and it feels sooty, or even a better description...resiny.
Is this due to overboosting and slightly blown headgaskets or what?

I have a Banks 6gun+SL, and occasionally get on the throttle pretty good.
I have no fluid leaking on the block, or in the driveway, nada nowhere.
So Im wondering if anyone has ever heard of this phenomenon before?
Thanks much in advance.

Rob

[SCUFFY828]

r u sure its not oil, and have you had a egr cooler put in anytime

[LvTitan]

it is most likely oil. i have some in my tank too because when i did a complete tear down of my motor and rebuild i'm sure some of the oil got into the cooling galleys before the heads were torqued down etc...

[RobFish]

Ive never had any warranty work done at all. I was thinking about taking it into the dealer (its got 29k miles) and having them run the usual tests for EGR valve, EGR cooler, headgaskets, leaks of any kind, but I live in San Diego and the closest mod friendly dealer I have heard about is an hour north of me.
The truck runs like a champ. Pulled the trailer with no probs whatsoever.
I plan on doing studs in the future, but I figured that I would wait until I was told that I had blown gaskets.
I agree it seems like its oil, but how would it get into the cooling system besides passing through during those moments of extreme boost levels.
Rob