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Cooling System: Frequently Asked Questions
by Larry Carley copyright 2023 AA1Car.com
The service life of the factory antifreeze in most late model vehicles is 5 years or up to 100,000 miles. The best advice for how often the coolant should be changed is to follow the service recommendations in your owners manual.
You can buy chemical test strips at auto parts stores that can be dipped in the coolant to reveal its condition. The test strips react to the corrosion inhibitors in the coolant, and if the inhibitors are depleted (worn out), the test strip will tell you the coolant is bad and needs to be changed.
When changing the coolant in your cooling system, use the same type of coolant that was put in when your vehicle was new (there are a variety of different types). Or, you can use a universal coolant that is approved for use with most vehicles (there may be exceptions!). Refer to your owners manual for the recommended type of coolant to use.
The capacity of your cooling system will vary depending on the year, make, model and engine in your vehicle. Typically, the cooling system capacity is a couple of gallons, but may be less for a small car or more for a larger SUV or truck. Again, we recommend you refer to your owners manual to determine the coolant capacity of your cooling system.
If you are using "pre-mixed" coolant (a blend of 50 percent water and 50 percent antifreeze), just add the recommended amount of coolant until the system is full.
If you are using "straight" coolant (not pre-mixed with water), add equal amounts of clean distilled water and antifreeze when refilling your cooling system. Do NOT use ordinary tap water because it contains minerals that are corrosive and may shorten the service life of the corrosion inhibitors in the antifreeze.
Getting all the air out of the system can be tricky, however, and may require starting the engine, letting it run until it is warm, then shutting the engine off, carefully venting the system and adding more coolant until the system is full.
Most antifreeze is Ethylene Glycol (EG) with various corrosion inhibitor additives to protect the metal components in your cooling system. Most brands of antifreeze contain corrosion inhibitors that will protect both aluminum, cast iron, steel and brass components.
WARNING: Ethylene glycol is poisonous if ingested. Do not leave open containers of antifreeze sitting around if you have pets or small children who may be tempted to drink the sweet smelling liquid.
When mixed in equal portions with water (a 50/50 mix), ethylene glycol will lower the freezing point of the coolant to about -34 degrees F, and also raise the boiling temperature to about 226 degrees F (depending on the pressure rating of the radiator or coolant reservoir cap).
Unless you live in an extreme climate (extremely hot or extremely cold), most vehicle manufacturers recommend using a 50/50 mixture of antifreeze and water.
Straight ethylene glycol antifreeze with no water added freezes at about -8 degrees F., but can provide freezing protection down to -60 degrees F when used in a 60 percent antifreeze/40 percent water mixture.
A mixture of 70 percent antifreeze and 30 percent water will provide freezing protection all the way down to -84 degrees F, and boilover protection up to 276 degrees F. with a 15 PSI pressure cap.
Do NOT dump used antifreeze on the ground or down a storm sewer as it will kill both plants and fish. It will also contaminate ground water.
The best way to get rid of it is to take it to an auto parts store, quick lube shop or local hazardous waste disposal facility for recycling.
However, in many cities, used antifreeze can be safely and legally disposed of by pouring it down your toilet if your plumbing is connected to a municipal waste disposal system.
Do NOT pour it down the toilet if your plumbing is connected to a septic tank because it will kill the good bacteria in the tank and contaminate ground water (which may kill grass, plants, trees and bushes near the drainage field!).
The most common mistake that is made when changing coolant is not getting all of the air out of the cooling system.
Air trapped under the thermostat can prevent coolant from filling the void in the engine block and/or cylinder heads. Some thermostats have a small "jiggle valve" or pin hole that allows trapped air to vest past the thermostat when the cooling system is being refilled. But if your thermostat lacks this feature, it is usually necessary to start the engine and let it warm up until the thermostat opens. This will open the vale and allow trapped air in the engine to pass. You then shut the engine off, and add more coolant until the system is full. You may have to repeat this step a couple of times to get all of the trapped air out of the system.
Air can also get trapped inside the heater core when changing coolant. To get the trapped air out, set the heater controls to a high temperature setting. Then start the engine and let the system warm up. When hot coolant starts to flow through the heater core and you can feel warm air blowing out of the ducts, any air that was trapped in the heater core should now be gone. As before, shut the engine off, recheck the coolant level and add as needed.
NOTE: On some vehicles, a professional level scan tool can be used to command the heater control valve open so that it will not block air or coolant while refilling the system.
Another common mistake when refilling the cooling system is using the WRONG type of coolant (one that is not recommended for your vehicle, or that is not compatible with the original coolant that was in the system before).
Another common mistake is refilling the cooling system with straight antifreeze, straight water, or too strong or too weak of an antifreeze/water mixture.
Straight antifreeze does not carry heat away from the engine as efficiently as water or a water/antifreeze mixture. During hot weather a cooling system that is filled with straight antifreeze or an overly strong mixture of too much antifreeze and not enough water (more than 60/40) may allow the engine to run hot and overheat.
Refilling a cooling system with straight water (little or no antifreeze) is a BIG mistake because water provides ZERO corrosion protection, no freezing protection below 32 degrees F, and will boil at 212 degrees F (increasing the risk of overheating and boilover).
If your temperature light is on, your engine is running dangerously hot. You should pull over as soon as it is safe to do so, shut the engine off and wait for it to cool down. While you are waiting, open the hood and look for signs of coolant leaking from the radiator, hoses or engine.
WARNING: Do NOT open the coolant reservoir or radiator cap while the engine is hot. Pressure that has built up inside the cooling system can force hot coolant and steam to blow out of the cap, possibly burning you! Wait at least 20 minutes to open a coolant reservoir or radiator cap if you can't see the coolant level in the transparent plastic coolant reservoir.
Overheating can be caused by a variety of things (see the next question).
A low coolant level, usually because of a coolant leak somewhere in the cooling system (radiator, hoses, heater core, or a bad head gasket).
A defective electric cooling fan that is not turning on when the engine is getting hot.
A bad radiator that is leaking or has an internal blockage that restricts coolant flow through the radiator, or a buildup of dirt, dead bugs, leaves or other debris on the outside of the radiator that restricts air flow through the radiator.
A pinched or restricted radiator hose that inhibits the flow of coolant between the engine and radiator.
A bad water pump with a loose or badly worn or corroded impeller inside the pump, or an electric water pump that is not working.
A severe exhaust restriction caused by a clogged catalytic converter, pinched or crushed exhaust pipe or a bad muffler with an internal blockage. Any of these will cause exhaust heat to back up in the engine and make the engine run hot.
Mild overheating will usually cause no damage. But severe engine overheating or continuing to drive mile after mile while your engine is running hot may crush the head gasket and cause the gasket to leak coolant and/or compression.
A damaged head gasket will allow coolant to seep from the engine's cooling jackets into the cylinders and down into the crankcase where it will contaminate the oil and cause sludge to form. The result can be damaged cylinder bores, piston rings, pistons and bearings.
Head gaskets are difficult and expensive to replace. However, if the damage to the gasket is not too great, it is sometimes possible to temporarily seal a leaky head gasket with special chemical sealer products that are added to the cooling system. Follow the directions carefully to get the best results.
The problem might be a low coolant level, a thermostat that is not closing to maintain normal engine temperature (or a missing thermostat if somebody removed it), a defective heater control valve or clogged heater core, or a stuck HVAC air control door that is not allowing air to flow normally through the heater core.
The coolant sensor monitors the temperature of the coolant so the engine control computer can regulate the fuel mixture, ignition timing and other emission functions as the engine warms up. Many of these functions depend on temperature, so if the coolant sensor is not reading correctly or is defective, it can affect how engine runs, performs and how much pollution it emits.
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