corrosion

Having a problem I can't resolve, looking for ideas:

steel Dart block 406, aluminum heads, aluminum water pump. I've tried Water Wetter and Hyperwet additives. I've tried straight tap water (well with softener), and tried distilled water. I've flushed the system multiple times until water comes out clear, then added the additive and topped off. I've tried every combination of these procedures. Still get a lot of corrosion in water. Brown, not sludgy. I take some out and let it sit in a jar. The sediment sinks to the bottom. So I know it's not oil in the system.

Ideas on what I'm doing wrong? Water pump impeller rusting? Not flushing enough?

Possible electrolysis. Make sure you have good shiny clean electrical grounds and even adding the OEM braided strap from engine to chassis is NEVER a bad idea.

Your probably not doing anything wrong when a block rust up on the inside the only thing that will get it clean is being baked and hot tanked. Doesent matter how many times you flush it it won't stop. Typically doesent cause any problems. It's real common in a engine that sat for a while with no coolant and the system open

Try distilled water....pita but your water source is likely pretty rusty with iron. Bad for your ticker as well as the engine.

Get a water softener.

If you have no means of filtering the air that the radiator pulls back in when cooling down, you will get dirt drawn back into the system.

I like a catch tank with a fuel filter on its vent.
Also keeps radiator full of coolant.

If using extended life coolant, distilled water is a must.

I always like to run at least 30% antifreeze in the cooling system, whether the rules allow or not. Antifreeze has corrosion inhibitors in it........if the antifreeze gets under 25%, one risks growing biological critters. Electrolysis is also possible with straight water. Also, antifreeze is actually corrosive if the system is allowed to dry out. If one ever does an engine service that requires draining the coolant system, one can store the water pump and thermostat in a bucket that contains the coolant that was removed from the engine. If the water pump or thermostat is allowed to dry out, either will most likely fail immediately after beeing returned to service. If I was going to store an engine that has antifreeze in the cooling system, I would either store the engine with coolant in the engine, or I would VERY thourgoughly flush the coolant system prior to dry storage.

Distilled water and check grounds.