could use help with coolant system - 2000 lumina

So I was checking the coolant level in my mother's 2000 Lumina, and when I opened the coolant resevoir, I noticed that all of the coolant looked like mud, the level was low, and there was nasty residue all over the inside of the tank. This car only has about 50,000 miles on it, and the engine runs great (the temperature needle is a bit below middle, almost low, even with the "mud" running through it...). I was thinking the best thing to do is to flush the entire coolant system, and was hoping someone had any suggestions as to the best way to do this. I don't know the car very well, and can't see any drainage plugs on the radiator or block. Is it necessary to detach one of the radiator hoses to drain the system, and then repeatedly cycle fresh water through the system to flush out the coolant in the block? Also, what could cause this on a car this new? (2000 is new for me... :) ). Any suggestions would be great

Ephram

check the oil. Is it milky brown? Might have a blown intake gasket or head gasket.

You -are- due for a coolant flush, regardless of its condition, but sludgy is common of old coolant. You'll find that true in either green or dex-cool systems; old coolant is sludgy, muddy, gel-like, etc. HOWEVER. Check when the engine's hot and the hood up; is there a strong smell of coolant? Check the oil just to be safe: if its brownish like chocolate milk/pudding, or gravy, then you might have a blown intake, like Blake said.

Best way to verify this is clean out the resivoir (take it off the car if you need to), drain the system by either taking off the lower radiator hose or, if you want "the right way", there's a drain cock on the lower driver's side that unsnaps with a 1/4" socket extension. Once you drain it then replace the lower hose, pop off the upper hose, point it downwardish, and stick a water hose in the radiator fill. Crank it up and let it run a few cycles of opening and closing the tstat. I know, that's not the GM Specified Certified By The Book way of flushing, but it works just fine for me.

Refill the system, bleed the air (pretty critical), and check it in a week or so. If its down low again, you know you've got a problem.

Thanks for that information, the oil looked fine (quite dark, overdue for a change). I guess GM's claim of 150,000 mile coolant is a little exadurated.

Its 150,000 or 5 years, whichever comes first. Age of coolant is, to me, more important than the actual mileage its seen. Different than oil.

The mud is usually caused by mixing dex-cool and regular green coolant, I see it all the time at work. You have to use a good cleaner to get rid of the mud and then flush the system.

Dexcool doesnt have to have 150k to turn to mud. Just a little air sucked in to the sysetm by the ever failing lower intake manifold gasket can give you chocolate pudding. If you are lucky (I use that term with some reservation), it leaks to the outside, as mine did. If not, it leaks to the inside and mixes with your oil. Am in the middle fixing problem (1999 3.1l) at this time.

Thanks for all of the replies. I started the flush today, and when I drained the coolant from the radiator, it looked alright, if a little bit old. I think the gunk left in the coolant resevoir was just sediment that had accrued there over a long period of time, and never mixed with the circulating coolant since the coolant level was low.