All modern automobile engines are “water-cooled” which means they use circulating fluid to carry heat from the engine to a radiator, where it is cooled and circulated back. Coolant is about 50% water, and the balance is made up of a variety of chemicals and additives. These lower the freezing point, improve the heat absorption capacity, resist corrosion, and sometimes, compounds that seal up porous castings or plug tiny leaks. “Antifreeze” is another name for coolant.
Most manufacturers recommend replacing the coolant as part of routine maintenance. This varies from vehicle to vehicle, and the specific recommendation will be found in the owner’s manual, but the average is about every 3 years or every 50,000 miles. That can be done by simply draining the system and refilling it. However, a much better result is gained by flushing the cooling system, and that is what is usually recommended.
Cost of a Coolant System Flushing
The average cost of a coolant flush can vary from $100 to $200. Some of the reasons for the variety in the cost are the differing labor rates and the cost of different vehicle-specific coolants. A significant part of the cost is the quantity of the materials. This is because some vehicles with smaller engines take less than 2 gallons of coolant, while a light truck with a diesel engine might take more than 5 gallons. OE coolant costs from $12 to $25 a gallon on average, so it does add up. The coolant necessary for each vehicle is usually included in the price of the service.
Another factor in the cost of a coolant flush is whether or not a flushing compound is used. Typically, a compound will be added to the cooling system, run for a few minutes to circulate through the engine and get it up to operating temperature, and then, remove the old coolant. The idea is that it dissolves and suspends old deposits; allowing them to be flushed out more thoroughly. Then, the system is refilled with a new, clean coolant. A flushing compound isn’t always used and isn’t always necessary, but it is part of the cost if it is done.
Why Does Coolant Need to be Serviced?
Over time, the coolant can react with the various surfaces it’s in contact with. Many coolants have specific anti-corrosion additives that act by coating the metal surfaces of the engine and radiator, and these additives do become depleted with time. “Long-life coolant” is just coolant that has additives that last longer. Some are supposed to be good for up to ten years, though normal maintenance and coolant freeze-protection checks still apply.
Coolant compounds can also break down over time from the heat, from contact with the atmosphere (in the coolant reservoir), from simple age, etc. Coolant that has lost its valuable properties can cause internal corrosion.
One of the most important features of coolant is its resistance to freezing, and if the coolant quality isn’t adequate, it can cause significant engine damage. That is one of the main things that can be tested for during a vehicle inspection.
Water expands when it freezes and has enough force to crack even an engine block, which is one of the reasons that engine blocks have freeze plugs that can pop out and relieve pressure in that situation.
How to Service the Cooling System
The most common method is “drain and fill”. Often, there is a radiator petcock that can be opened to drain the coolant. Then the petcock is closed, and the system is refilled with new coolant. That’s the simplest. Sometimes there is no petcock, and the lower radiator hose can be pulled instead, accomplishing the same thing. With either of these methods, sometimes it’s necessary to purge the air from the system afterwards. This is best done with a vacuum device; trapped air is suctioned out, then the system is topped off with new fluid, and then the vehicle is run up to temperature and topped off. This is common enough now that most shops are equipped, but using a flush machine avoids that issue.
With a flush machine, fill and drain ports are installed (usually temporarily) inline with either the upper radiator hose or the heater hoses. Then the vehicle is brought up to temperature, which opens the thermostat, and new fluid is pumped in while old fluid is sucked out. A flush machine has the advantage of not introducing air, and it replaces more fluid than a drain and fill.
What Else Might be Recommended?
Generally, a coolant flush is done as part of a scheduled service at a fixed interval. There isn’t really anything else in the cooling system that would be replaced at an interval like that, but most shops would inspect the system for leaks first. It’s not uncommon to find signs of a water pump leaking, even before it has caused any symptoms or problems. There’s a little weep-hole on the nose of most pumps that allows any coolant that has gotten past the impeller seal to exit the housing. Any signs of dried coolant will usually get you an estimate for a new water pump.
Related Article: Water Pump Replacement Cost Guide
If the coolant is in bad shape or if there has been any overheating, it’s not uncommon to get a recommendation to replace the thermostat. That is a valve that usually sits at the upper radiator hose inlet on the engine block, and allows coolant flow once a certain temperature is reached. The thermostat is easily damaged by overheating, and by corrosion. It’s also fairly inexpensive and easy to replace in most cases, and is often replaced along with any cooling system maintenance.
Related Article: Thermostat Replacement Cost Guide
It’s hard to know in most cases, so the general rule is to assume the answer is “no”. There are three main types of coolant used by manufacturers now, and these are generally not safely compatible. Sometimes they are identifiable by the different dyes used, but that’s not always a reliable indicator.
Chrysler, for instance, used a pink coolant mix for a time, then switched to a purple mix that is incompatible with the pink. They congeal and can block the cooling system if mixed. One unfortunate tendency of the purple mix is that it tends to turn more orangish/pinkish as it ages, making mistakes all too easy. Most shops will verify the correct coolant from spec sheets or the owner’s manual if there is any doubt.
Manufacturers make coolant with specific mixes to work best with the metals and gasket materials that the engine uses. A little money can be saved by using an aftermarket universal coolant that meets many different specs, but it’s not always possible to gauge the suitability of a universal coolant mix for a specific engine. Generally, if the OE coolant is not being used, the least universal or most vehicle specific aftermarket coolant is the safest choice.
The main difference is often the kind of fluid used. A dealership will typically use OE fluid. A chain will often use the same universal fluid on all vehicles. An independent might use a vehicle-specific aftermarket fluid. It’s not a bad idea to ask in advance.
Yes, but first make sure you’re set up to safely catch the coolant that is drained, as it can be poisonous to pets and animals. And then there is the possibility of getting air trapped in the system when refilling, which can only be easily gotten out with special tools. The sign of that would be overheating or the failure of the engine to stabilize at the normal running temperature.