Over time, engine coolant loses its protective power. Old coolant leads to all kinds of engine performance and cooling system trouble:
- Radiator hose damage
- Radiator leaks
- Engine bearing damage
- Blown head gasket
- Sticky exhaust valve stems
- Warped cylinder head
- Overhead cam damage
- Cylinder damage
- Engine bearing damage
Replacing the coolant in your engine is part of your vehicle's preventive maintenance. It helps avoid coolant breakdown, and damage to system components and other engine parts. Usually, you should replace your engine's coolant every two to four years, depending on your particular model. Consult your car owner's manual or repair manual.
You Should Have a Manual
It's a good idea to have the repair manual for your particular vehicle make and model when replacing the coolant in your system. Your manual will help you:
- Locate components.
- Check the recommended coolant for your system.
- Drain the cooling system.
- Check coolant capacity.
- Bleed the system.
- Monitor for cooling system issues.
You can buy a relatively inexpensive manual through Amazon.
Haynes manuals include:
- Step-by-step procedures
- Photos and illustrations
- Systems descriptions
- Diagnostics and troubleshooting
- Location of parts
- Electrical diagrams
- Maintenance schedule
Also, using your manual to follow your car maintenance needs will help you avoid unnecessary breakdowns. So you'll recoup your small investment in a short period.
The following sections help you replace the coolant in your vehicle.
In This Article
- How Much Electrolysis is Going On in Your Cooling System?
- Draining Engine Coolant
- A Simple Method for Flushing the Cooling System
- Refilling With Fresh Coolant
- Bleeding the Cooling System
- Servicing Hybrid Vehicle Cooling Systems
- Resources to Help You With Electrolysis and Cooling System Issues
Never remove a radiator cap when it's hot to the touch, boiling coolant can gush out and seriously burn your skin.
1. How Much Electrolysis is Going On in Your Cooling System?
It's a good idea to check for the presence of electrolysis in your cooling system before replacing the coolant, especially if you've noticed starting or some other electrical issues.
Electrolysis is the flow of electrical current through water. As coolant wears out, its content of acid, salts, and minerals increases, and so it becomes a better electrical conductor. Electrolysis can be accelerated if there are faulty grounds in the engine or electrical accessories.
Electrolysis in a cooling system destroys the protective layer from inside the radiator tubes. Eventually, it leads to radiator leaks and engine damage.
You can perform the following simple test, using a digital multimeter capable of measuring DC (direct current) voltage and AC (alternating current) voltage.
- Pop the hood open.
- Make sure the engine is cool.
- Remove the radiator cap.
- Set your multimeter to DC Volts.
- Choose a low setting so you can read tenths of a volt.
- Attach the meter's negative (black) lead to engine ground; usually, the alternator case or mounting bracket is a good place.
- Submerge the meter's positive (red) lead into the coolant through the radiator neck, but don't allow the lead to touch the radiator.
- Ask an assistant to start the engine and pay attention to the voltage reading while the engine is cranking.
- Record this measurement.
- Keep the engine running.
- Ask your assistant to turn on all the accessories (radio, lights, wipers, AC).
- Take another coolant voltage measurement.
If your vehicle has a cast-iron engine, a normal voltage reading will fall between 0 and 0.3 volts.
A vehicle with a bi-metal or aluminum engine will produce a normal reading between 0 and 0.15 volts.
Repeat the same procedure, but this time set your DMM meter to read AC voltage and record your results.
If you detected high DC voltage while the engine was cranking, check engine grounds, the radiator cooling fan, and the air conditioning fan as well, if necessary. See the Resources section at the bottom of this post for help on this, and your vehicle repair manual.
If you detected high DC voltage while the accessories were turned on, ask your assistant to turn off each accessory one by one while you monitor voltage levels. When the voltage drops, the accessory that was just turned off is the one with ground issues. Check and correct this ground.
If you detected high voltage during your AC voltage tests, there's some static electricity. This is usually built from the coolant solution rubbing against two different metal components like a cast iron engine block and an aluminum cylinder head, radiator or heater core.
If electrolysis is higher than normal, it is a good idea to flush the system before replacing the engine's coolant.
2. Draining Engine Coolant
Before you start draining your coolant, verify your vehicle's coolant capacity, so you can find out how much remains after you drain it. Consult your car owner's manual or repair manual. In most cases, about 30 to 50 percent of coolant remains in the system after draining.
- Open the hood of your vehicle and wait for the engine to cool, if necessary.
- Set the heater to the maximum HOT position, so the coolant reaches the heater core as well.
- Remove the radiator cap.
- Remove the coolant overflow tank and empty the coolant into a catch pan.
- Position the catch pan under the radiator drain plug and remove the plug. If your radiator has a petcock, open it fully. If your radiator doesn't have one, carefully detach the lower radiator hose instead to drain the cooling system.
- When coolant stops draining, replace the plug or hose.
- Consult your vehicle repair manual to locate any engine drain plugs. You can remove this plug to drain coolant stuck in the engine block.
- Apply sealant to the plug threads and reinstall the engine drain plug to the torque listed in your repair manual.
- It's a good idea to flush the system (see the next section) to remove any remaining coolant from the system, and remove as much dirt, rust, and metal shavings from the bottom of the radiator. If you suspect the radiator is partially plugged, remove it and have it serviced instead.
- After flushing, refill the system with fresh coolant.
3. A Simple Method for Flushing the Cooling System
You can use plain water to flush your cooling system. If you decide to use a flush chemical from an auto parts store, make sure it is safe for the type of radiator you have. And thoroughly read the instructions that come with the product you are using.
1. Fill the cooling system with regular water.
2. Start the engine and let it reach operating temperature.
3. Shut off the engine and let it cool.
4. Drain the water.
4. Repeat this procedure until you see clear water coming out of the system.
The following section explains how to bleed the cooling system of trapped air after refilling the system.
4. Refilling With Fresh Coolant
You can find pre-mixed coolant ready to use. If you buy antifreeze, mix it with distilled water before use, and check the coolant system's capacity. In most cases, you'll use a 50/50 mixture of antifreeze and water; but in regions that experience extreme weather, manufacturers may recommend a 70/30 mixture. Consult your car owner's manual or repair manual.
High- and low-quality aftermarket antifreeze products abound, with different chemical composition, including extended-life coolants.
The following table shows the most common types of coolants. It's better to base your selection according to the specification listed in your car owner's manual or vehicle repair manual, or information from a reputable automotive shop.
Colors of Pre-Mixed Coolant
|Color||Makes that use it|
Many Ford, Chrysler, European models
VW, GM, Saab
Turquoise (Hybrid OAT)
Tesla, BMW, Volvo
Usually older models
Hyundai, Honda, Toyota, Nissan
VW, Audi, Mercedes-Benz, Porsche
4. Bleeding the Cooling System
Refilling the cooling system with new coolant will usually trap air that can lead to hot pockets and overheating. These pockets can ruin the cylinder head gasket, cylinder walls, and the rest of the cooling system.
Trapped air is more of a problem in newer vehicle models that place the radiator top on a lower level than the top of the cooling system in the engine's cylinder head.
Some vehicle models come with air bleed valves. Check your car owner's manual or repair manual for the correct steps to bleed the system in your vehicle.
Here is a simple procedure to bleed the system:
- Jack up the front of the vehicle, if necessary, so the radiator cap sits at a higher position than the top of the engine.
- Support the vehicle on jack stands.
- Chock the rear wheels with a pair of wooden blocks or something similar.
- Set the transmission to Neutral (manual) or Park (automatic).
- Install the radiator cap to its first lock position.
- Start the engine and let it reach operating temperature. This allows the thermostat to open and trapped air to flow and exit through the radiator neck.
- Shut off the engine and top off the cooling system with fresh coolant.
- Reinstall the radiator cap to its full lock position.
- Lower the vehicle from the jack stands.
Check the overflow tank level during the following week and top off the system if necessary.
Bleeding the Cooling System Using a Funnel
In the following video, you'll see how to add coolant and bleed the cooling system at the same time using a coolant funnel kit you can buy through Amazon. The funnel makes it more convenient to replace the coolant, preventing air pockets in the system.
Disposing of Used Coolant
Never pour coolant into the sewer or the ground. Coolant is a hazardous waste and should be recycled or disposed of according to local laws and regulations.
5. Servicing Hybrid Vehicle Cooling Systems
Hybrid vehicles require special knowledge and precautions due to the configuration and operation of their cooling system.
For example, Ford uses two different cooling systems on some models, one for the engine and another one for hybrid components. You may be able to service the engine cooling system by isolating a high-voltage circuit. Still, you need to check the repair manual for your particular model and follow a specific procedure.
On some Toyota hybrids, the coolant may circulate under pressure even hours after shutting off the engine. You'll have to disconnect the electric water pump before replacing the coolant. Yet, air pockets can easily find their way into the system, so you need to be careful. And purging the system may require a scan tool. Consult the repair manual for your particular model.
6. Resources to Help You With Electrolysis and Cooling System Issues
- Why Is My Car Overheating?
Find out why your engine is overheating by focusing on the conditions under which the problem manifests itself, narrowing down the possible components or systems that could be behind the problem.
- Coolant Loss: Where Is My Car's Coolant Going?
Learn how coolant loss happens, where to look for the leak, and what tests you can do at home to find the leak source faster.
- Coolant Temperature Sensor Test
This coolant temperature sensor test will tell you in just a few minutes whether you need to replace it.
- Troubleshooting Electric Cooling Fan Problems in Cars
Check for cooling fan problems using this simple guide and tips.
- Diagnosing the Symptoms of a Bad Engine Ground
Checking for a bad engine ground can fix dimmed lights, faulty sensors, and hard starting, and it can prevent severe damage.
- Automotive Voltage Drop Testing
How to use a voltage drop test to troubleshoot common automotive problem circuits to speed up repairs and save money.
This article is accurate and true to the best of the author’s knowledge. Content is for informational or entertainment purposes only and does not substitute for personal counsel or professional advice in business, financial, legal, or technical matters.
© 2022 Dan Ferrell