Radiator sludge is essentially nothing more than corrosion and debris that accumulates and thickens in your cooling system. If sludge is allowed to continue building up without being flushed out from time to time, it can cause serious problems for your cooling system.
Radiators, especially older radiators, are made of metal. You then fill them with a mixture of fluids, primarily antifreeze and water. Over time, the inside components of the radiator and the rest of the cooling system can rust and corrode, creating debris in your cooling system. The debris settles into the bottom of your radiator and builds up until it has formed a sludge by mixing with the water and antifreeze.
Problems with your intake manifold gasket can cause oil to mix with your coolant, filling your radiator and cooling system with an oily sludge. In this case, your cooling system is not where the problem originated, but if it goes undetected or is not properly flushed back out when your repair your car, you will develop serious cooling problems from the sludge.
Dex-Cool and General Motors Vehicles
If your GM vehicle is having problems with radiator sludge or overheating, you may need to check your antifreeze. Dex-Cool, which has been commonly used in General Motors vehicles as an antifreeze solution, has been linked to repeated cooling system problems and sludge build up according to Consumer Affairs. Among the problems linked to Dex-Cool are unusually high sludge build up and cooling system damages. In 2008, GM settled with vehicle owners who experienced problems and repairs related to Dex-Cool. If you have radiator sludge problems and own a General Motors vehicle that is using Dex-Cool or came from the factory with that coolant, you should discuss your options with a mechanic.