Brown sludge in Coolant, 2004 GTP CompG

I have a 2004 GTP Comp G and I found a brown oily sludge build up in the coolant resevoir and the radiator filler.

I drained the coolant and flushed the system with water several times before adding new coolant. I used Prestone Extended Life coolant that is compatible with DexCool (red/orange color).

After several months the sluge returned. After searching the forum and other info online, it seems like there are two possible causes for the sludge.

The first is what seems to be a "normal" sludge buildup in DexCool. There seem to be mixed opinions on the sludge buildup problem with DexCool. I haven't seen any abnormal loss of coolant or oil.

The second is a possible intake manifold gasket leak allowing oil to enter the coolant. Since my 3800 series III engine has a supercharger, it seems like the manifold problems are less likely. Most of the posts that I saw with this problem had the plastic manifold.

Any thoughts or suggestions would be appreciated.

Well, the most common problem is the Coolent seeping into the valve covers where the oil is in there, and or oil getting into your coolent. Whats the sludge smell like? and are you noticing a decrease in your Oil level? and a increase in your Coolent Level?

The sludge doesn't smell unusual. It smells like coolant. The oil level may be going down a little faster than it has previously but nothing dramatic. The oil usage is on the order of 3-4 oz per 1000 mi. It has 94,000 miles. The coolant level hasn't changed.

Well, did you get a complete Coolent system flush, mabey there is just still sludgy crap still in there and it just got mixed with the new coolent. If not, you most likely have the famous gasket leaks of oil mixing with coolent and the other way around.

Well, my CompG has 34XXX miles on it and my coolant looks like new.

However, my wifes 2000 GP SE had the lower intake gasket problem and the coolant looked like sludge.

Off of that, I'd say you have a leak somewhere, but these cars have so many little irks that it may be ok, but I doubt it. It didn't seem like hers was leaking oil either, but after a while that oil will take it's toll.