Just as important as motor oil to an engine, radiator coolant shares an equal responsibility for keeping power to the wheels. It is also one of the most overlooked bits of service most cars receive during their life cycle. It is this lack of coolant maintenance that contributes to many mechanical breakdowns due to engine cooling problems.

Engine Coolant Basics

Antifreeze serves three necessary functions in an automobiles cooling system.

• It removes heat from the engine and carries it away to the radiator where it dissipates into the passing air.
• It lowers the freeze point of the coolant well below that of straight water, and raises the boiling point to prevent overheating.
• Protects internal engine and radiator components from corrosion and scale. Either of which will restrict coolant flow or reduce the cooling systems effectiveness.

Types of Antifreeze

Ethylene glycol (EG) is, and has long been, the primary ingredient in most antifreeze formulations. EG coolants traditionally contain corrosion inhibitors such as silicates, phosphates and borates. Each in different proportions depending on the type metal it is protecting.

Propylene glycol (PG) is a newer base stock in some antifreeze formulations. It is considered non-toxic, and therefore less harmful to people and the environment. Although PG coolants provide adequate protection for engines and radiators, it is not as effective as Ethylene glycol.

Standard vs. Extended Life Coolants

The glycol fraction of antifreeze never wears out. However, the corrosion inhibitors in the antifreeze do get used up over time. For this reason, antifreeze replacement is necessary periodically.

Standard antifreeze most often used in older vehicles lasts up to two years or 30,000 miles depending on driving conditions and environment.

Extended-life coolants, widely introduced in the 1990’s, retain their effectiveness for up to five years or 150,000 miles. The difference being, the corrosion inhibiting additives are much slower acting, and therefore last longer.

Engine Coolant Color

There is no universal standard establishing the dye color for different types and manufacturers of antifreeze. While GM’s branded coolant is orange, Subaru’s recommended coolant color was green and now is the new Super Coolant, which is blue. But even this knowledge does not account for the many aftermarket coolants available with varying degrees of protection, and in every color of the spectrum.

With this said, chemical composition and manufacturer recommendations always trump coolant color.

Mixing Coolant Types

Unlike yesteryear, all antifreeze is not alike. Engine manufacturers have developed formulas of coolants specific to their cars. A coolant that provides extended, worry-free, performance in a Ford vehicle, will not work as effectively in a Subaru.

Additionally, the additive package in one brand of coolant, may not be compatible with the existing coolant in a car’s radiator. The combination of the two can destroy seals, gaskets or hoses in time.

Engine Coolant Flush

When a coolant change is undertaken, especially when switching from one coolant to another, a complete radiator flush will ensure the task is successful. Simply draining a radiator similar to changing engine oil, will leave up to half of the old coolant in the system.

Flushing the system also removes any scale and sediment that may be reducing the cooling capacity of the radiator.

Most coolant system problems are avoidable through periodic inspection and routine maintenance.

Antifreeze 101

First it should be noted that coolant and antifreeze are the same thing. Replacing the vehicles engine coolant is part of a routine vehicle maintenance regiment, but how often should the coolant be replaced? Many auto shops will recommend a flush instead of a straight coolant replacement. What’s better for the vehicle, replacing the coolant or flushing the radiator? Find out the answer to the question, radiator flush or engine coolant replacement.

How Often Should the Engine Coolant Be Replaced?

The best answer to the question of how often engine coolant should be replaced is to find out what the vehicle manufacturer recommends. The vehicles owner’s manual should have a maintenance schedule that shows what mileage intervals the engine coolant should be replaced. If the vehicles owner’s manual is missing, the dealer or the manufacturers website should have the needed information. When replacing engine coolant, it's best to go over the cooling system check list.

Older vehicles usually require that the engine/radiator coolant be replaced every 30,000 miles. Most new vehicles from 2003 and up have a green coolant (newer vehicles blue coolant) that should last up to 100,000 miles. The manufacturers maintenance schedule will have the mileage intervals required. It’s important to note that most manufacturers do not recommend a coolant flush but simply recommend replacing the engine coolant.

• With a radiator coolant drain and refill the coolant is simply drained from the radiator and refilled. Most radiators have a drain on the bottom of the radiator called a petcock. The petcock is simply turned and the coolant will drain from the petcock. If there is no petcock, the bottom radiator hose can be removed to drain the coolant.
• After the radiator is drained, close the petcock and refill the radiator, usually with a mixture of half water and half coolant. Auto parts stores usually have straight coolant or containers that are premixed with water. Make sure the correct coolant is used to refill the radiator. If the vehicle is equipped with a coolant recovery tank, make sure the tank is at the level indicated on the tank.

Cooling System Flush

When the vehicles radiator is drained, most of the coolant in the engine remains. With a cooling system flush auto shops will either manually flush the cooling system or use a flush machine.

• Manual Flush – When the cooling system is flushed manually, a flush solution is poured into the radiator. The cars engine is then ran until it reaches operating temperature. This allows the thermostat to open and coolant to run through the entire cooling system. The radiator is then drained and refilled with coolant. Old coolant will still remain in the engine.
• Coolant Flush Machine – With a flush machine the coolant is forced through the cooling system and virtually all of the old coolant is removed from the cooling system. With a simple drain and refill a lot of rust and other contaminants remain in the engine. With a manual flush more contaminants are removed but some still remain.

Other Chemicals Used With a Cooling System Flush

Naturally a flush cleaning agent should be used when a coolant flush is performed. Some other chemicals that might be used may included the following:

• Chemical Flush – Cleans the cooling systems and removes rust, other contaminants and deposits
• Lubrication – Sometimes auto repair shops will use a lubricant that lubricates the water pump and other components to help increase the life of those components.
• Sealants - Some experts say that a cooling system flush may break loose contaminants that may cause leaks. As a precaution they may add sealants that will actually work to seal leaks before they occur.

Whatever choice is made between a drain and refill or a flush, there are some experts that claim that a flush machine may cause more damage by breaking loose components. If a cooling system flush is performed, it’s best to make sure that there is a guarantee or warranty against future problems like coolant leaks. Most repair orders that are signed by the vehicle owner at the auto repair shop state that no expressed warranties apply. If there is a warranty, make sure that the warranty is in writing.

Purging Trapped Air (Suggestion)

WARNING:

The radiator is of the pressurized type. Do not attempt to open the radiator cap immediately after the engine has been stopped.

1) Lift up the vehicle.

2) Remove the under cover.

3) Place a container under drain pipe.

4) Loosen and remove the drain plug to drain engine coolant into the container.

5) For quick draining, open the radiator cap.

CAUTION:

Be careful not to spill coolant on the floor.

6) Drain the coolant from reservoir tank.

7) Tighten the radiator drain screw securely after draining coolant.

8) Slowly pour the prepared coolant from radiator filler port to neck of filler, then pour into the reservoir tank up to “FULL” level.

Coolant capacity (fill up to “FULL” level)

• Non-turbo AT model: Approx. 6.9 Litres (7.3 US qt, 6.1 Imp qt)
• Non-turbo MT model: Approx. 7.0 Litres (7.4 US qf, 6.2 Imp qt)
• Turbo AT model: Approx. 7.6 Litres (8.0 US qt, 6.7 Imp qt)
• Turbo MT model: Approx. 7.7 Litres (8.1 US qt, 6.8 Imp qt)

9) Securely install the radiator cap.

10) Run engine for more than five minutes at 2,000 to 3,000 rpm. (Run until radiator becomes hot in order to purge air trapped in cooling system.)

11) Stop the engine and wait until coolant temperature lowers. Then open the radiator cap to check coolant level and add coolant up to radiator filler neck. Next, add coolant into reservoir tank up to “FULL” level.

12) After adding coolant, securely then install radiator and reservoir tank caps.