Dirty coolant in over flow tank?

I recently purchased an 04' "program" MC for an exceptional price. It's not perfect, but runs and drives great.

Other than some minor body work that was done, the only concern I have is that the coolant in the overflow tank was really bad looking(very dark and thick). The trans. fluid and oil levels are stable. I am going to change the coolant this weekend, and keep an eye on it.

Has anyone ever noticed this on other 3.4L engines??

Thanks for all replies.

Sounds like your coolant became contaminated, which is a problem with Dex Cool antifreeze. Something as simple as air getting into the cooling system can cause contamination.I'd give the cooling system a good flush, and in the future keep an eye on the level in your overflow tank to make sure it remains within the reccomended range, adding new coolant mix to top off. I'd also continue to monitor your other fluid levels. Also I'd reccomend changing the coolant at least every 2 years/ 30,000 miles as long as you own the vehicle, as the Dex Cool does not last as long as previously thought.

One more thing. When you flush your cooling system out, make sure you thoroughly clean out any junk in the overflow tank before refilling with the new coolant mix.

Thanks for the reply.

After some more investigation, I think this is somewhat common. I also have a 97 Tahoe that the coolant seemed ok but I had to replace the intake gasket @ 80000 miles.

I plan to drain the system and flush with water, and replace the coolant. Does anyone have any other suggestions?

Replace radiator cap, pretty common source of air leakage into the cooling system it seems.

I have the same problem with my 98 and I used a radiator flush twice to get the sludge out and it is still there. I replaced the cap as well and flushed out the overflow. It's nasty and sticks like nothing I have ever seen before. I will do it again tomarrow and let you know what the 3 time gets me. I wish you luck o the water but I would recomend some type of cleaner. I went with the cheap stuff. Maybe it would be worth the extra few bucks to only have to do it once.

I have a 97 monte and I just flushed my coolant system. There is a new coolant out there that can be used with dexcool equiped cars or with the regular coolant. It's green just like the regular, but it is compatible with dexcool. I don't think that dexcool is going to be on the market for much longer because my local Auto Zone already does not stock it anymore.

Have you ever thought about flushing the system and then replacing w/regular antifreeze?