Checking and changing the coolant in today's cars has become a lot more complicated due to different coolant requirements, so here are some tips to keep in mind:
All cars and light trucks require at least a 50/50 mixture of antifreeze and water for adequate freezing, boiling and corrosion protection. A 50/50 mixture will provide freezing protection down to -34 degrees F with ethylene glycol (EG) antifreeze, and -26 degrees F with propylene glycol (PG) antifreeze.
If you are using a hydrometer to check the concentration of antifreeze in the coolant, keep in mind that the specific gravity of conventional EG antifreeze is different from that of PG (which has a density close to water). So if someone has added the "less-toxic" PG antifreeze to the cooling system, you will either need a special hydrometer to measure the concentration of the coolant or a refractometer (which works with either type of antifreeze).
Increasing the concentration of antifreeze in the coolant can provide added freezing protection in really cold climates, but the maximum mix for EG antifreeze is 70%. When hot weather returns, the coolant should be diluted back to 50/50 because antifreeze cools less efficiently than water.
The next thing to check is the condition of the coolant. The leading cause of radiator failure is corrosion due to lack of cooling system maintenance. The corrosion inhibitors in conventional antifreeze are gradually depleted over time, so the recommended coolant change interval has traditionally been every two years or 24,000 to 30,000 miles for preventive maintenance.
The new "extended service" antifreeze formulas that can go 5 years or 150,000 miles between changes reduce the need for cooling system maintenance and can reduce the risk of premature radiator failure. But some older vehicles still have antifreeze with conventional additives in their cooling systems. So when regular coolant checks and changes are neglected, the risk of corrosion rises sharply with each passing year.
Checking the pH of the coolant with chemically-treated test strips can help you determine the condition of the coolant. But be warned that today's coolants typically operate at lower reserve alkalinity (RA) levels than they used to. The alkalinity of a typical antifreeze/water mixture will vary depending on the additive package in the antifreeze and may vary from 8 to 14. The average used to be around 10.5, but some of the extended life coolants now maintain corrosion protection at a pH of only 8.3. Depending on the pH test strips used, it is possible to get a false indication of bad coolant. To get an accurate reading, therefore, you have to know what kind of coolant is in the system and use the appropriate test strips to check it.
Unfortunately, identifying the type of coolant that is in the cooling system is not always easy. You can't go by color because it varies, Most conventional two-year antifreezes for north American domestic vehicles is dyed green. But Saturn and some European makers also use green dye for their extended life coolants. DEX-COOL extended life coolant, which is used in 1996 and newer GM vehicles, is dyed orange to distinguish it from ordinary antifreeze. If intermixed with other types of antifreeze, the color may or may not change depending on the dosage. GM warns that intermixing extended life coolant with ordinary coolant reduces the coolant's life to that of the ordinary coolant.
To add to the color confusion, some European and Korean coolants are dyed blue. Mercedes uses a yellow dye in its coolant. Toyota's new extended life coolant is dyed red. Intermix any of the above and its hard to tell what color the coolant may become.
The real difference between all these EG coolants is in the additive package. Traditional antifreeze formulas for domestic applications with aluminum radiators, cylinder heads or blocks contain a high level of silicates (which is not really needed in cast iron engines with copper/brass radiators). Silicates form a protective barrier on aluminum that protects the metal. The additives in European and Asian OEM antifreezes, however, contain less silicates and rely mostly on borates to inhibit corrosion. European antifreezes also contains no phosphates because hard water can react with phosphates to form calcium and magnesium sediments. The Asians use phosphates but no borates and low or no silicates because they say borates may actually add to the aluminum corrosion problem if the coolant is neglected.
The extended life coolants use an entirely different corrosion inhibiting chemistry that uses carboxylate organic acids instead of the silicates, phosphates or borates.
To reduce confusion, several antifreeze suppliers (Peak and Prestone) sell a "universal" type of antifreeze that is compatible with all types of antifreeze and all makes and models of vehicles. Some argue this is not entirely true, but the stuff seems to work okay and is widely accepted in the aftermarket.
When adding or changing coolants, the best advice is to follow the recommendations of the vehicle manufacturer. Replace same with same, if possible, using the same type of antifreeze that was in the system. This information can be found in your Owners Manual, or it may be marked on the radiator cap or coolant reservoir. Or, use a universal coolant that is approved for ALL applications.
What kind of coolant is best for older cars? If your car or truck is more than 15 years old and has a bimetal engine (iron block and aluminum heads) and an aluminum radiator, the best protection will probably be provided by a HOAT or G-05 coolant that contains silicates. Silicates helps protect aluminum against corrosion. On the other hand, if you have an older vehicle with an iron or bimetal engine and a copper/brass radiator, use a traditional GREEN formula coolant. The additives in traditional coolant provide better protection for copper/brass radiators.