Engine Coolant

When the combustion engine of an automobile generates energy, it also generates a great deal of heat.  These engines are typically “water”-cooled by the engine’s coolant with the main coolant purpose being to effectively remove this heat and allow the car to function properly.  Besides cooling the engine, coolant also protects against engine corrosion, heat transfer, freezing temperatures, and extremely high temperatures.  

Coolants were developed to overcome the shortcomings of water as a heat transfer fluid and typically contain ethylene glycol and other additives which inhibit corrosion, lubricate water pump seals and otherwise facilitate the system functionality.  Coolants (as compared to water) will have a lower freeze point and an elevated boil point ensuring its capacity to perform in all situations encountered in the environment. Other names for engine coolant are anti-freeze, anti-boil, and radiator fluid. 

The higher the percentage of ethylene glycol in the coolant allows the engine to run at higher and lower temperatures than a coolant with a lower percentage of ethylene glycol.  For example, a coolant with 30% ethylene glycol and 70% water protects from 1° F to 250° F while a coolant with 70% ethylene glycol and 30% water protects from -83° F to 276° F.  See the table below for a more detailed breakdown.

% Ethylene Glycol

% Water

Lowest Temperature

Highest Temperature

30

70

1° F

250° F

40

60

-9° F

260° F

50

50

-35° F

264° F

60

40

-61° F

270° F

70

30

-83° F

276° F

*Chart from http://www.coolantexperts.com/

There are three types of Ethylene Glycol found in coolant today:

Green Coolant – Green coolant is silicate based and is almost non-existent in newer cars today.

Organic Acid Technology (OAT) – Formulated without the use of silicates & allows for a longer coolant life. 

Hybrid Coolant - Hybrid coolants are OAT coolants with a silicate charge added. 

Most cars are using OAT or Hybrid coolants.  Which kind depends on the individual manufacturer so it is important that you check your owner’s manual for details on your specific car. 

Over time, coolant begins to become more acidic and could lead to corrosion of your car’s engine parts.  In order to keep your engine running correctly you must flush the coolant periodically and replace it.

The life of the coolant depends on its ability to inhibit corrosion. Silicates, phosphates and/or borates are used as corrosion inhibitors to keep the solution alkaline. As long as the coolant remains alkaline, corrosion is held in check and there's no need to change the coolant.  But as the corrosion inhibiting chemicals are used up over time, electrolytic corrosion starts to eat away at the metal inside the engine and radiator. Aluminum is especially vulnerable to corrosion and can turn to Swiss cheese rather quickly when conditions are right. Solder bloom can also form in copper\brass radiators causing leaks and restrictions. So changing the coolant periodically as preventive maintenance is a good way to prevent costly repairs.

The basic idea is to change the coolant before the corrosion inhibitors reach dangerously low levels. Historically, auto manufacturers have recommended changing coolant every 2-3 years or 30,000 miles.  While that is a good idea to follow, some of the newer coolants, “long life” coolants, last closer to 4-5 years or 50,000 miles.  Following the OEM change recommendations is usually good enough to keep corrosion in check, but it may not always be the case. That's why more frequent changes may be recommended to minimize the risk of corrosion in bimetal engines and aluminum radiators.
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