John Baker | Mar 2, 2016 9:00:00 AM Nearly 40 percent of engine failures can be attributed to cooling-system issues. Clearly, it pays to take care of your vehicle’s cooling system. Sludge/slime are just one of the common symptoms of larger problems. Left unchecked, it’ll plug the radiator, heater core or fluid passages, resulting in overheating and expensive repairs. What causes it, and what can you do about it? • Additives dropping out – coolant consists of a base (typically ethylene glycol or propylene glycol) mixed with additives and water. The base is primarily responsible for providing freeze and boil-over protection. The additives guard against corrosion, cavitation and scaling. Mixing of incompatible coolants, however, can cause the additives to “drop out” of the ...