There are many different coolant types in use today with different formulas and applications. These include:
One thing the aftermarket has always been good at is consolidation, and today's coolants leave plenty of room for that. In the past couple of years, many antifreeze suppliers have introduced "universal" or "global" one-size-fits-all coolants that are claimed to be compatible with alol makes and models, including both newer and older vehicles.
The basic idea behind universal coolants is to eliminate all the confusion about colors and chemistry and have one basic product that works in any vehicle regardless of year, make or model. What could be simpler?
Not all antifreeze suppliers buy into this marketing philosophy, however, so you'll still see the three basic types of coolant being marketed: traditional green for older vehicles and budget-conscious motorists who want the least expensive product on the shelf, an extended-life product that is compatible with Dex-Cool and other OAT-based coolants, and a hybrid OAT for late-model Ford, Chrysler and European vehicles that specify G-05 coolant. But for those who offer a universal "all makes and all models" kind of product, the advantages are obvious: one product that provides full coverage for all applications.
Makers of universal coolants say their products are formulated to be compatible with all cooling systems (import or domestic) and all coolant types (traditional green, OAT and OAT-hybrid with silicate). The new universal coolants use unique OAT-based corrosion packages with proprietary organic acids (such as carboxylate) to provide broad spectrum protection.
When a universal coolant is used to top off a cooling system that already contains an extended-life OAT or hybrid coolant, the service life is unaffected. It remains five years or 150,000 miles. If a universal coolant is added to an older vehicle that has traditional green antifreeze in the cooling system, the service intervals is also the same as before: two to three years or 30,000 to 50,000 miles depending on what was in the system.
Checking the strength of the coolant is important to make sure the coolant contains a high enough concentration of antifreeze to prevent freezing during cold weather, and also prevent boilover during hot weather. You can use a hydrometer or a refractometer for this purpose, but a refractometer usually provides the most accurate results.
If the concentration is low, drain some coolant from the radiator and replace with a compatible antifreeze to increase the freezing protection. A 50/50 mixture of ethylene glycol antifreeze and water will keep the cooling system from freezing up all the way down to -34 degrees F. Increasing the mix to a maximum of 70 percent antifreeze will keep the coolant liquid down to -84 degrees F!
Caution: Never use straight undiluted antifreeze or straight water! Straight antifreeze does not have the heat carrying capacity of water, and may cause the engine to overheat. Straight water provides no freezing protection, no boilover protection and no corrosion protection.
When adding water to a cooling system, use distilled water only. Do NOT use "softened" water because it contains dissolved salt, which can be corrosive, or hard tap water because it contains dissolved minerals that can form lime deposits.
One of the best ways to check the condition of the coolant is to use chemical test strips. The test strips change color to reveal both the condition and strength (freezing protection) of the coolant. The test strips react to the level of alkalinity or acidity in the coolant to give a "good" or "bad" reading. If the anti-corrosion additives are depleted, the coolant is overdue for a change regardless of time or mileage. Just make sure you use the correct type of test strip for the coolant being tested (regular or extended life). And if you're not sure what's in the cooling system, use a test strip designed for regular coolant.
A visual inspection of the coolant is also a good idea to check for sediment or other signs of contamination. Droplets of oil in the coolant might be the result of a leaky ATF cooler or a leaky head gasket. The presence of sediment or rust would tell you the coolant is not doing its job of protecting your cooling system, and is long overdue for replacement.
If you own a GM vehicle with Dex-Cool and the coolant is full of red muck (which GM says can occur if the cooling system has not been filled properly and there is air in the system), you have a serious problem that will likely require flushing and cleaning the entire cooling system, and possibly replacing the radiator if the muck cannot be removed. The most troublesome applications have been Chevy/GMC S-10 pickups and Blazer/Jimmy models with the cast iron 4.3L V6 engine. These trucks do not have a pressurized coolant reservoir and seem to be prone to air contamination of the coolant.
With older "conventional" green-formula North American antifreeze, the recommended replacement interval is usually every two years or 30,000 miles.
The same recommendation applies to extended-life coolants that have been contaminated with ordinary coolant. If you use ordinary coolant to top off your coolant reservoir or radiator, and your system is filled with extended-life coolant, the additive packages can interact and reduce the service life to that of regular coolant.
Long-life coolants are NOT lifetime coolants. They can last up to five years or 150,000 miles, whichever comes first, but not forever.
If your old coolant is full of rust or sediment, or your engine has been running hot because of lime deposits inside the engine's cooling jackets, flushing is recommended to clean out the contaminants. The first step would be to add a bottle of cooling system cleaner to the coolant, and then run the engine for the recommended time so the cleaner can loosen rust and other deposits. Follow the directions on the product for best results.
After the cleaner has had adequate time to work, the cooling system can then be drained followed by flushing or reverse flushing with clean water to remove as much residue as possible. continue flushing until the water coming out of the radiator is clear.
Annual coolant flushes are NOT necessary - unless your cooling system contains ordinary antifreeze and you drive more than 30,000 miles a year, or your cooling system is contaminated with rust or sediment from past neglect.
If your are switching to a universal coolant, the cooling system should be flushed to remove all traces of the old coolant before the new coolant is added. Just draining and refilling the radiator is not a complete coolant change because up to a third of the old coolant can remain in the block. If the old coolant is ordinary green coolant, the new universal coolant will be diluted and won't be able to extend protection much beyond that of the original coolant.
The best way to assure a thorough flush job is to take your car to a service facility that has a coolant exchange machine. These machines do an excellent job of replacing almost all of the old coolant with new coolant. It costs more than doing it yourself, but it also saves a lot of hassle, assures a complete coolant exchange and eliminates the problem of disposing of the old coolant (they will recycle it for you).
Coolant recycling machines take a different approach by filtering and replenishing the old coolant that is already in the vehicle. Corrosion protection is restored by adding new chemicals to the coolant. Universal additive packages are also available for use with recycling machines, or conventional or OAT-based additive packages for domestic or Asian/European applications.