I have drained and replaced the coolant more times than I want to say and each time the water/antifreeze is dirty black. If allowed to sit in the container a black substance settles to the bottom and is really messy almost like carbon black.

The engine is a 305 V8 with about 46500 miles and runs reasonably well. There is no oil in the water nor is there water in the engine oil.

Does anyone have an educated reason for the condition?

Thanx

blown head gasket!

...If allowed to sit in the container a black substance settles to the bottom and is really messy almost like carbon black.
Well, if it was oil it would float to the surface so it's not that.

It may be some type of radiator "stop leak" that the previous owner put in. I once had a Camaro that did the same thing. The stop leak settled in the heater core and no amount of flushing the engine would get rid of it. Try flushing the heater core.

I brought it in to my favorite shop and they just notified me that it is not a blown headgasket. So I suppose it will be returned with the same problem. :x

Any new ideas?

Flush the system with a premium Quality flush. Replace the hoses, if you haven't already, all of them. If that doesn't fix the issue, you should consider having the radiator cored and rodded or just a new radiator.

If your hoses are old it could be that they are rotting inside and that is the black garbage your seeing. If it is then sooner, than later, your going to blow a hose.

So flush it, replace all the hoses, thermostat etc.... Contaminates can sit in the block or the Radiator or the heater core for a long long time, for ever actually if they're heavy enough with rust and that type of trash especially if it's mixing with some Barg's leak or other stop leak.

Just a thought.

Given the head gaskets are good, then draining is not enough. I've had this happen a few times before with older cars, in fact, we fixed one a couple of weeks ago. Time to get serious with cleaning the system.

Get a coolant system cleaner and use as directed. Then, buy one of the Back-Flush kits and use it thoroughly as directed. Fill with water and drive it. No use wasting more coolant until you get the crud out of the block or radiator. Obviously, it's there somewhere in the system and it may take 2 or 3 flushes. Also check to make sure there are no metal slivers where you drain.

Soon it will clear up and you'll have saved a lot of money. Worse case is you'll find something else wrong and you'll want to know about it anyway.

Take care.

I got the elky without a coolant tank and i put one in. my antifreeze isnt black, it just turned to a brown, dirty green as soon as i drove it. is antifreeze supposed to get a little dirty?

If you had aluminum heads or an aluminum radiator, I'd blame it on electrolisis which they make special caps for (and fluid too I believe). If it's all stock than I'm stumped. Just clean it up as best you can. If it doesn't overheat, I wouldn't worry about it too much.