By Ralph Kalal

You knew you had to worry about the freeze protection offered by antifreeze. But, do you need to worry about your coolant’s pH, as well?

Many mechanics claim that testing the pH level of antifreeze is an effective way of determining its condition. Some professional repair shops offer additives ostensibly intended to insure a proper pH in your antifreeze.

Here’s the pitch: water has a pH of 7.0 and antifreeze has a pH of 10.5, so a 50-50 mix has a pH of 8.75, and that’s too acidic to protect the cooling system, so the pH must be modified to something around 10 to protect the dissimilar metals in the modern cooling system. And, further, antifreeze must be frequently replaced to ensure proper pH.

The pH value is a way of expressing the relative acidity of coolant. Acidity does cause corrosion. There are even reported instances of old coolant becoming so acidic that it turns the entire engine into, in effect, a battery, affecting electronic engine controls.

Look closely, though, and you’ll notice that the typical pitch for replacing antifreeze (because it has the wrong pH) simply equates the pH of water to the pH of conventional green ethylene glycol antifreeze at a 50-50 mix, and then claims that the resulting number is too acidic.  

That comparison ignores the corrosion resistant formulations built into modern antifreezes, especially the Dex-Cool and G-05 long-life formulations. These antifreezes are designed to have a lower pH than conventional ethylene glycol antifreezes; 8.3 compared with 10.
Test strips that can be dipped into the antifreeze to determine the pH level are available at auto parts stores, if you want to check your antifreeze’s pH level.  

With but one exception, it is not a good idea to supplement Dex-Cool or G-05 with additives, even those claiming to be compatible with those products. The corrosion-resistant capabilities of OAT antifreezes are the result of its organic chemical structure, the same chemical structure that delivers its freeze protection.  

The sole exception is when the manufacturer says to put something else into the antifreeze solution, as specified in either the owner’s manual or the factory shop manual, in order to address a specific coolant concern. Cadillac, for example, specified the addition of “coolant tablets” to antifreeze in pre-2000 Northstar engines to eliminate a porosity problem with the aluminum engine block casting that could lead to coolant leaks.  

Last, but certainly not least, is whether the antifreeze in your car offers adequate protection against freezing. You can test this.

antifreeze tester


Test it with a “coolant hydrometer” available at any auto parts store. This inexpensive device measures the specific gravity of the coolant. It does not, however, tell you anything of the corrosion protection capabilities remaining in the coolant. Simply insert the tip of the hydrometer into the antifreeze and pull some into the chamber, enough that the float lifts free. The reading tells you the freeze protection.