All automotive engines create heat as a by-product of combustion. Modern engines are designed with a cooling system to regulate this heat. They perform best when operated between 180 and 210 degrees Fahrenheit. If an engine runs colder than this, fuel economy and emissions suffer greatly. Engine life suffers to some extent. If they run hotter, engine life can start to suffer greatly. Cooling systems use a fluid that transfers heat from the engine to be dissipated into the air through a radiator. The fluid in cooling systems is an ethylene glycol based fluid called coolant or antifreeze. It stands up very well to the constant heating up and cooling down that it goes through on a daily basis. However it can wear out from use. The harder a cooling system has to work, the shorter the lifespan. Running a vehicle with worn out coolant can cause expensive damage. The coolant wears out slowly. Usually a driver does not realize it has happened. For this reason we recommend coolant fluid to be replaced between 90,000 and 100,000 miles. Coolant holds up very well for this length of time unless it is exposed to air. This can happen if a cooling system operates low on coolant. This can corrode and erode the inside of a cooling system very fast. Corrosion deposits will restrict the system causing it to be less efficient. Erosion can make holes in the system causing leaks. If this happens just changing the coolant may not be enough. In these cases we recommend the system be flushed. This will usually get most of the corrosion contamination out of the system. If a system has been badly contaminated, just one flush may not clean out all deposits. Keep in mind, if deposits are bad enough, they can stop up a hole. The flush uncovers it and then it will start to leak.