In order to remove hardened scale, a direct chemical action is necessary. Add a flushing compound in a dissolved solution at the specified rate of 30 grams per liter (4 oz per gallon) of radiator capacity to the coolant water. Do this while the water is running. Operate the engine for 15 minutes. Then, drain and flush the system with clean water.

There are various types of flushing compounds available commercially. Obtain the compounds from a reliable source. Most compounds attack metals and should not remain in the engine block for more than a few minutes. Use a neutralizer in the cooling system immediately after you use a descaling solvent.

Use a stronger solution for extremely hard, stubborn coatings, such as lime scale. The corrosive action of a stronger solution affects the thin metals of the radiator, which reduces the operating life of the radiator. A complete flush and rinse of the radiator is mandatory and must be accomplished skillfully.

Drain the entire system after the solvent and neutralizer are used and the cooling system is flushed. Fill the system with a 50/50 mixture of distilled water and an ethylene glycol-based coolant (DEX-COOL™). Inspect for coolant leaks in the radiator, the hose and the engine.