Among other things I am responsible for maintaining several large cooling systems that use glycol for its antifreeze properties.
Glycol comes in several forms; ethylene, and propylene are common types used for heat transfer systems.
In my experience most automotive cooling systems use ethylene glycol.
Pure ethylene glycol is very stable:
Until you add water to it, heat it, and aerate it.
Remove any of the three reactionary factors and it remains relatively stable.
Glycol is inferior to water as a heat transfer fluid.
Pure glycol does not transfer heat very well compared to water.
Glycol is added to water solely for antifreeze and boil over protection.
Basically when glycol is mixed with water; more heat, and more aeration equals more decomposition.
The decomposition products contain an acid.
The acidic decomposition product attacks most substances in the cooling system.
To counteract this unhappy circumstance glycol based coolants contain additives.
These additives are designed to retard the reactions that produce acids, and neutralize the acids once formed.
For routine maintenance we monitor Ph.
When Ph is below a certain number (I believe 7.0 is the cutoff)
either the additive is replenished or the coolant is changed out.
In addition to additive replenishment we use a bypass filtration system that is based on 15 micron filtration of the coolant.
Dow chemical tells me that with proper maintenance ethylene glycol can be maintained for more than 20 years!
Its the additive package that makes a huge difference, as well as keeping air and sediments out of the system.
It is common knowledge in my industry that a sealed cooling system is superior to an open to air system (using glycol).
In other words if the expansion tank is not pressurized it will expose the coolant to more air which will allow more acids to be produced.
And as a final somewhat non-applicable note:
In my world of megawatt RF transmitters; pure water (distilled) is preferred due to its non corrosive and electrically non conductive nature.
We even go to to the point of maintaining an electrical conductivity monitor, and a Ph monitor with remote alarms.
Of course our transmitters are never shut down.
And still some of the more modern transmitter designs spec glycol based coolant for boil over protection.
I wont go into the pure water systems that use vapor phase cooling as this does not apply to automotive cooling (normally !).
Rickey.
Glycol comes in several forms; ethylene, and propylene are common types used for heat transfer systems.
In my experience most automotive cooling systems use ethylene glycol.
Pure ethylene glycol is very stable:
Until you add water to it, heat it, and aerate it.
Remove any of the three reactionary factors and it remains relatively stable.
Glycol is inferior to water as a heat transfer fluid.
Pure glycol does not transfer heat very well compared to water.
Glycol is added to water solely for antifreeze and boil over protection.
Basically when glycol is mixed with water; more heat, and more aeration equals more decomposition.
The decomposition products contain an acid.
The acidic decomposition product attacks most substances in the cooling system.
To counteract this unhappy circumstance glycol based coolants contain additives.
These additives are designed to retard the reactions that produce acids, and neutralize the acids once formed.
For routine maintenance we monitor Ph.
When Ph is below a certain number (I believe 7.0 is the cutoff)
either the additive is replenished or the coolant is changed out.
In addition to additive replenishment we use a bypass filtration system that is based on 15 micron filtration of the coolant.
Dow chemical tells me that with proper maintenance ethylene glycol can be maintained for more than 20 years!
Its the additive package that makes a huge difference, as well as keeping air and sediments out of the system.
It is common knowledge in my industry that a sealed cooling system is superior to an open to air system (using glycol).
In other words if the expansion tank is not pressurized it will expose the coolant to more air which will allow more acids to be produced.
And as a final somewhat non-applicable note:
In my world of megawatt RF transmitters; pure water (distilled) is preferred due to its non corrosive and electrically non conductive nature.
We even go to to the point of maintaining an electrical conductivity monitor, and a Ph monitor with remote alarms.
Of course our transmitters are never shut down.
And still some of the more modern transmitter designs spec glycol based coolant for boil over protection.
I wont go into the pure water systems that use vapor phase cooling as this does not apply to automotive cooling (normally !).
Rickey.
