Today's cooling systems have not changed much from vehicles in the past. Except for an electric cooling fan in most models, modern cooling systems work nearly the same as your grandparents' vehicles. However, the penalty for procrastination is much greater. As you already know, today's vehicles are much harder to work on and require more time to repair. This has translated to higher repair costs for internal engine repairs. All of the symptoms below should be repaired as soon as possible to avoid unnecessary repairs.
Your cooling system should be flushed and 'pH balanced' at least every 30,000 miles or two years (whichever comes first). Flushing your cooling system, and most importantly, pH balancing your anti-freeze, will help reduce the acid level in your cooling system that promotes electrochemical reaction. This reaction causes degradation of the cooling system components. Flushing and pH balancing the coolant will save you money by extending the life of your radiator, heater core, water pump, head gaskets, radiator hoses, heater hoses, and freeze plugs.