Originally Posted By: Koz1
Google says. Mechanics Forum.
Getting rid of those deposits is tedious but not difficult:
Drain the coolant and flush with tap water (dispose of the coolant safely!)
Fill the cooling system with about two cups of liquid dishwasher detergent dissolved in hot water.
Start the engine and run it until it warms up to regular operating temperature.
Drain the detergent solution and flush with tap water again until it runs clean. (The idea here is to remove all oils from the system.)
Fill the cooling system with two pounds of citric acid powder (available from industrial chemical supply houses, or from Mercedes-Benz dealers at a considerable premium) dissolved in hot distilled water (since your tap water is hard).
Again, start the engine and run it until it warms up to regular operating temperature, or at least fifteen minutes.
Flush with distilled water. At this point you should see all sorts of rust, mineral deposits, and miscellaneous crud loosened by the citric acid come out of the drain hole.
Refill the system with the appropriate mix of coolant and distilled water. Use a modern "long-life" orange coolant if you have an aluminum cylinder head, block, or both--green coolant promotes corrosion in aluminum.
Instead of Citric acid you could try vinegar.
It could take a lot of distilled water to flush all the [censored] out, several flushes.
I would first do the citric acid flush THEN the detergent flush. The system should get some kind of neutralizing treatment after the acid flush, and the detergent flush would do that.