Antifreeze Deterioration


Rising Sun Member
Aug 24, 2005
Kittredge CO, USA
It's (fairly) common knowledge that antifreeze has to be changed out of our cooling systems about every two years because the corrosion inhibitors break down and the coolant becomes acidic. What I've been trying to find out is what causes the breakdown. Is it simply from sitting around? Is it from contact with metal, hoses and stuff? Is it from sitting around after it's been mixed with water? Is it from thermal cycling?

The reason I ask is that they're giving away 150 gallons at work and I can get maybe 5 gallons or so for free if I want it, but I don't know if it's any good. It's in 55 gallon drums. It's been sitting in these drums for at least 10 years, maybe more. If it's no good I'll pass.

I can easily measure the pH (we manufacture pH meters, among other instruments), but I don't know how much of a pH shift means that the corrosion inhibitors have deteriorated. Anybody know more about this?