Replacing Engine Coolant

Replacing Engine Coolant

Cooling system failure is the most common cause of engine-related breakdowns. A few things that can help prevent this from happening is replacing engine coolant regularly, keeping the radiator’s coolant filled, using the right type of coolant (whether regular or the extended life kind) and knowing the precise application of coolant:water ratio. But before we continue, here’s a brief summary on how a cooling system works.


Green engine coolant being poured into engineSome of the heat created from an engine’s combustion process is expelled into the exhaust system, and any heat that was not dispersed in this way stays in the car engine. Engineers devised liquid-cooling and air-cooling, two kinds of cooling system that reduces residual heat, keeping the temperature balanced. Some older model of cars, but only very few of the modern ones, are air-cooled. The engine block has some kind of fins that convey the heat off the cylinder instead of having the fluid circulate through the engine. A powerful fan, ala 1965-1989 Porsche 911s, is often used to force the air over the fins, cooling the engine when heat transfers into the air.

A radiator is used conversely in liquid-cooled cars for heat dissipation. A type of heat exchanger, a radiator is designed to shift heat from the engine when the coolant flows through it passing to the radiator and then dissipating to the air. The coolant passes from the inlet into the outlet through some of the tubes mounted in a parallel arrangement. The fins conduct the heat from the tubes and transfer it to the air flowing through the radiator.

A car can function in varying temperatures, ranging from below freezing to heat about over 100 F (38 C) . The fluid to be used in cooling the engine should have a high boiling point, as well as a very low freezing point, and should have the capability to handle a lot of the heat.

While water is an effective fluid and is most commonly used in holding heat, it shouldn’t be used by itself in the engine because it can easily be susceptive to freezing. Most cars use antifreeze, a kind of fluid consisting of ethylene glycol and water. Adding water and ethylene glycol significantly improves the freezing and boiling points of the fluids. The cooling system also uses pressure to further raise the boiling point of the coolant. Just as the boiling temperature of the water is higher in a pressure cooker, the boiling temperature of the coolant is higher if you pressurize the system.

Temp Warning LightAntifreeze serves three purposes: It helps to keep the engine from overheating; it keeps the coolant from freezing and it helps keep cooling system components from corroding. Most of the Manufactures recommend a coolant mixture of 50% antifreeze and 50% water (preferably distilled water). A 50/50 level the antifreeze will protect the system from freezing down to –34 Fahrenheit and boil over to 265 degrees. The boil over point will depend on the pressure rating of the radiation cap. The higher the pressure rating of the radiator caps the higher the boil over temp.

For those wanting an even wider range of temperature variation, higher concentrations of antifreeze can be used to protect the cooling system in extreme conditions (for this area, CoHo Auto only uses a 50/50 mix). A 70% antifreeze and 30% water solution will protect the cooling system down to –84 degrees and boil over up to 276 degrees. But using anything higher than 70/30 should never be used since antifreeze does not carry heat as well as water and a higher level of a concentration could create an overheating condition. It should also be noted that antifreeze by itself will freeze at –8 degrees.

Car RaceEthylene Glycol, however, does nothing to prevent corrosion in the system. For that reason, corrosion-inhibiting chemicals are added to the antifreeze. In conventional phosphates, antifreeze, silicates and or borates are used in combinations to form a protective coating on the cooling system surfaces. Eventually heat and other conditions dissolve these inhibitors. Once these inhibitors are gone, the electrolytic corrosion begins to accelerate very quickly. The electricity flowing through the coolant system can cause pinholes to form in the heater core and/or the radiator. The first thing the electrolysis process will attack are aluminum components of the cooling system such as cylinder heads, intake manifolds, water pumps etc. Proper servicing of the coolant and correct installation of engine grounds can greatly reduce the electrolysis process. Generally speaking, the coolant needs to be replaced about every two years. Postponing this maintenance will actually accelerate the corrosion process rather than inhibit it.

Recently, some manufacturers have been installing extended life coolant in many of their vehicles cooling systems. This type of coolant contains special additive packages that can extend coolant life up to five years or 100,000 miles. These types of coolants can be used in any vehicle application old or new where long-term protection is desired – providing that the old coolant is completely flushed out the system before you install the extended life coolant. Volvo, for instance, uses a special phosefate free coolant in its cars even though it is green like conventional coolant. But when in doubt, check with the manufacturer. We don’t guess, and you shouldn’t either.

Flushing Coolant:

As is the case when changing brake fluid, there is a difference between a “drain and fill” and a complete coolant flush. We do not advocate just draining old antifreeze and then topping off the radiator. In brief, the effects of the “new” fluid will quickly loose their effectiveness because the “old” fluid will contaminate it.

carCoHo Auto uses a state-of-the-art BG CT2 Coolant Transfusion System to completely flush old coolant from the radiator, engine block and all hoses. We first add a cooling system flush additive to the existing coolant and let it circulate throughout the entire system for about 20 minutes (the additive essentially removes tough organic deposits that result from oil fouling, grease and glycol oxidation residues). After it has circulated through the entire cooling system, the old antifreeze is then back-flushed. This is the preferred method of replacing the old fluid since it removes scale and debris not accessible when the coolant flows in the normal direction. As the old antifreeze is forced out of the cooling system, the BG machine simultaneously introduces new fluid. Once all the old antifreeze has been replaced, we reconnect the hoses and thoroughly inspect the radiator cap, drain valve, overflow reservoir, and all connections for deterioration.

As a matter of routine, CoHo Auto also adds a cooling system conditioner to the new coolant. This conditioner contains a balanced combination of pH buffering ingredients that act as acid neutralizers, thus preventing corrosive damage to cooling system components. It also contains anti-foaming agents that help prevent bubbling in the system as well as oxide-forming ingredients that prevent corrosion of aluminum surfaces such as the radiator and the cylinder heads.


As part of our customer service program, CoHo Auto inspects and tops off all vital fluids on every car we work on – including the antifreeze or replacing engine coolant id necessary. But we usually don’t test the coolant unless asked. If you don’t remember when you last changed the antifreeze, or if you recently acquired a used car with no maintenance history, then we recommend having the fluid tested with a hydrometer. Hydrometers measure the specific gravity of the coolant, or in layman’s terms, tells you how acidic the antifreeze is and if it needs to be replaced. You can stop by virtually any automotive shop to have the coolant tested. This time of year is a good time to check the condition of this vital fluid – before the heat of the summer impacts us all.