sludge in antifreeze overflow tank 98-99 malibu

I have a 98 and a 99 malibu that has brown thick sludge in the antifreeze overflow tank. I have always had a problem w/ the antifreeze evaporating and I would have to replace it every 1 1/2 months..Had the dexcool taken out of it and the gaskets on engine replaced because of dexcool rotting problems..Use the green stuff now but it is all brown in the tank and the cap to the overflow is sludgy also..What is my problem before I bring it to shop where it will cost $$$. The low fluid light is on and won't go off even after I refill tank...Should I be putting it someplace else...Was told to replace it thru overflow tank! HELP!!!

I have a 98 and a 99 malibu that has brown thick sludge in the antifreeze overflow tank. I have always had a problem w/ the antifreeze evaporating and I would have to replace it every 1 1/2 months..Had the dexcool taken out of it and the gaskets on engine replaced because of dexcool rotting problems..Use the green stuff now but it is all brown in the tank and the cap to the overflow is sludgy also..What is my problem before I bring it to shop where it will cost $$$. The low fluid light is on and won't go off even after I refill tank...Should I be putting it someplace else...Was told to replace it thru overflow tank! HELP!!!

The brown crap could be the old coolant (dexcool) and the older green coolant mixing. Maybe the system was not flushed properly. You may also have a leak. Somewhere some how. Second, the light could be from the level sensor sticking. You are going to have to take the resevoir off and clean it.

Sounds like you have oil in the O-Flow tank which is none conductive. The oil is lighter than water so it stays on top. The low coolant switch uses the water to complete the circuit. If you have an auto trans? check the color of the fluid. The cooler could be bad in the radiator or maybe another source of oil infiltration?

Antifreeze does not evaporate. Missing antifreeze is either leaking or burning. Since your oil is also mixing with the antifreeze, you have a leaking intake gasket. Check the top of the block on the driver side and you'll find a puddle of antifreeze sitting there.

The brown crap could be the old coolant (dexcool) and the older green coolant mixing. Maybe the system was not flushed properly. You may also have a leak. Somewhere some how. Second, the light could be from the level sensor sticking. You are going to have to take the resevoir off and clean it.

I agree with this. I also think the dexcool was not flushed out properly and mixing with the green it looks brown. I seriously doubt you are getting oil in the coolant. I also think you still have a coolant leak, probably at the lower intake manifold gasket.