When a vehicle engine runs too hot, it can lead to everything from weaker performance to all-out failure. Internal combustion engines have several ways to help reduce temperatures. One of them is the use of engine coolant. Every modern gas and diesel engine uses coolant. While it may not get the same attention as other fluids like motor oil, coolant is essential for the powerplant to operate normally.
Knowing the basics about engine coolant will help you understand why it’s important, maintain a good maintenance schedule, and quickly notice any signs of trouble. After being bitten by oversight in the past, I always keep diligent tabs on my coolant and encourage others to do the same, so I put together this engine coolant guide to help you get started. Here’s everything you need to know about engine coolant for your vehicle.
What Is Engine Coolant?
True to its name, engine coolant helps keep the engine cool. But what’s in it? Originally, distilled water was used as a coolant for several reasons. Water has a high heat capacity and excellent thermal conductivity, making it an excellent cooling agent. It’s also cheap, non-toxic, and readily available. However, problems arise when temperatures get cold. Water freezes at 32 degrees Fahrenheit and expands when it freezes, rendering vehicles inoperable in cold climates and causing serious engine damage. Its boiling point of 212 degrees Fahrenheit can also cause pure water to vaporize in a hot engine.
As such, the water requires an additive. While various alcohols have been used, such as ethanol, most modern coolants are a mix of water and ethylene glycol. This organic compound has a freezing point of 10.4 degrees Fahrenheit and a boiling point of 387.1 degrees Fahrenheit in its regular state. When mixed with water, though, the combined solution can remain a liquid at even lower temperatures. For example, a mixture of 50% water and 50% glycol has a freezing point of -35 degrees and a boiling point of 223 degrees. (Because of this property, coolant is often called “antifreeze.”) The glycol also helps prevent rust and corrosion in the engine from water exposure.
How Does Engine Coolant Work?
Coolant is similar to oil in that it circulates through the engine and helps cool parts, but it follows a very different path. Special channels are built into the engine block and head for the coolant to pass through, drawing away engine heat as it does while also providing some lubrication.
Next, the coolant enters the bottom of the radiator on the driver’s side. The radiator is a form of heat exchanger. As the coolant passes through the metal fins in the heater core, the air blowing over them dissipates heat into the surrounding air. Finally, the coolant re-enters the engine from the top of the radiator. The various points are connected by flexible hoses, and a water pump drives the coolant through the engine. There’s also an expansion tank to catch overflow since the coolant can expand from the heat and pressure. Finally, an engine-driven fan helps dissipate heat when the vehicle is idling.
Using a separate set of hoses and lines, coolant also travels into your vehicle’s interior and through the cabin heater. This is essentially a small radiator inside your car and acts in the same way, releasing heat when it is turned on. Since you do not need extra heat inside the cabin during hot weather, the heater can be turned off. However, if your engine ever starts overheating, you can crank up the heater to add its additional small radiator to your cooling system to help.
When Should You Replace Coolant?
Like every fluid in your engine, the coolant has a shelf life. The glycol starts to break down, especially at higher temperatures of 230 to 250 degrees, eventually losing its antifreeze and anti-corrosion capabilities. Your coolant may also become contaminated.
Exactly how long you can drive between coolant changes depends on the vehicle, the type of coolant, where you drive, and other factors. The general rule is to change the coolant every three years or 50,000 to 60,000 miles. Some modern coolants, though, are rated for as long as 10 years or 300,000 miles. Conversely, other coolants may only last 10,000 miles, especially if you engage in high-performance driving or live in a brutal climate. For my vehicle, the manufacturer recommends more frequent coolant changes as the mileage increases since the engine is more prone to wear. Consult your owner’s manual and check the coolant label for more information.
Changing the coolant requires thoroughly flushing the cooling system with water and then adding fresh coolant, usually about five liters. Although you can do this at home, most people trust a professional shop. The antifreeze agents are toxic to humans and animals and require careful handling and disposal. An automotive shop has skilled technicians and supplies to do this, and they can also examine the system for leaks or other problems.
What Engine Coolant Mix Should You Use?
I mentioned already that coolant is a mix of water and antifreeze. There are different ratios, though, depending on your needs. A 50/50 water/glycol mix works well in most parts of the U.S., giving you good all-purpose protection and “burst point” reliability for the occasional cold snap or heat waves. In colder and hotter regions, though, you may need a higher glycol percentage. A 40/60 mixture, for example, lowers the freezing point to -49 degrees. Conversely, if you seldom or never use the vehicle in cold weather, a 60/40 or even 65/35 mixture may suffice. My vehicle owner’s manual has a table recommending what mix to use based on the ambient temperature.
Additionally, you will need to get the correct type of coolant. There are several classifications depending on the antifreeze inhibitor technology, and the color can usually identify them:
- Inorganic additive technology (IAT) coolants are generally used in older vehicles and are typically green.
- Organic acid technology (OAT) coolants are often found in GM, VW, and Saab vehicles and are usually orange or red.
- Hybrid OAT (HOAT) coolants, which are yellow in color, are common in Ford, Chrysler, and European vehicles.
- NAP-free HOAT coolants are found in many vehicles, including BMW and Volvo, and are often turquoise.
- Phosphated HOAT (P-HOAT) is popular in Asian vehicles like Toyotas and Hondas and is typically pink or blue.
- Silicated HOAT (Si-HOAT) is common in high-performance and luxury brands with a purple hue.
- Universal coolants can be blended with most other coolants and have varying colors, although they are mainly meant for short-term applications.
Unless you have a universal coolant, you should generally avoid blending coolant types. Reactions between the different chemicals can reduce protection or even create a system-blocking gel. I should note, though, that coolant color and vehicle associations are not hard-and-fast rules. Again, check your owner’s manual and the coolant label.
Signs You Need a Coolant Change
If a problem arises, you may need to flush the coolant earlier than the recommended intervals. Here are some signs that the system needs a flush.
- The coolant warning light on the dash comes on.
- You find yourself regularly having to top off the cooling system.
- Your car is overheating even when the cooling system is full.
- The coolant has turned brown or has visible debris.
- There is a syrup-like smell from the engine bay. (This is a sign of clogging.)
- The engine is making grinding or knocking sounds.
- There is visible coolant on the ground beneath the vehicle.
Be aware that coolant issues can often be symptoms of other engine problems, such as a radiator leak or blown head gasket. Bringing your vehicle to a professional will help you diagnose these issues.
Keep Your Engine Cool
A cool engine is a happy engine and one that will perform and last longer. By using the correct engine coolant, changing it at the proper intervals, and acting swiftly at the first signs of trouble, you can help your engine run at the proper temperatures. Use the information here as a jumping-off point to address this important aspect of engine maintenance.