Low coolant levels can quickly lead to an overheating engine, poor performance, and even severe engine damage if ignored. Fortunately, checking and refilling coolant is a relatively simple maintenance task, as long as it’s done safely and with the correct coolant type.
Safety Precautions for Coolant Refills:
- Park on a level surface with the parking brake engaged.
- Let the engine cool fully before you begin.
- Clean spills and dispose of any old coolant responsibly.
Steps to Refill Your Coolant:
- Identify your refill points. Depending on your vehicle, there could be caps on the radiator, reservoir, or expansion tank.
- Select the right coolant for your car.
- Unless it’s premixed, combine the antifreeze with the correct amount of distilled water, per the instructions.
- Open the cap(s) at the refill points and refill to the correct level.
- Close the cap(s).
- Drive the car with the heating on for approximately 30 minutes.
- Check the levels and add coolant again if necessary.
Read on to learn about this process in more detail, including symptoms of low coolant and what can cause repeated drops in engine coolant level.
This Article Contains:
- How to Put Coolant in a Car (Step-by-Step)
- What Happens When You Drive with Low Coolant?
- Why Your Coolant Level Keeps Dropping
- How to Choose the Right Coolant for Your Car
- 5 FAQs on Engine Coolant
How to Put Coolant in a Car (Step-by-Step)
If your cooling system is well-sealed with no leaks, your coolant level shouldn’t drop much over time. However, it’s still worth checking occasionally because a low coolant level can lead to overheating and engine damage. If you’re constantly losing coolant, there’s likely a coolant leak or another issue that needs diagnosing.
If you’re not confident with car maintenance, we recommend having a professional check and top up your engine coolant.
But, if you’d like to do it yourself, here’s what you’ll need:
- The correct type of antifreeze or coolant mixture
- Distilled water
- Rag
- Funnel
CAUTION: Antifreeze is poisonous to humans and animals. Thoroughly clean up any spills and properly discard the old fluid. Also, keep pets and small children out of the area whenever you work with antifreeze.
Now, here’s how to add coolant to your car:
Step 1: Park Your Car and Turn Off the Engine
Park on a level surface, set the parking brake, and let the engine cool completely before you begin. If the engine is hot, the cooling system is pressurized, and opening it can cause hot coolant or steam to spray out and burn you.
Step 2: Locate the Refill Points
Open the hood to find the caps through which you’ll refill your coolant.
There are typically three cooling system layouts:
- Older cars have a radiator with a removable radiator cap, plus a coolant reservoir or overflow tank. Both are refill points. The radiator is pressurized; the reservoir is not.
- Many cars have no radiator cap. Instead, a pressure cap sits on the coolant expansion tank, which is the sole refill point.
- Some cars without radiator caps have both a pressurized expansion tank and a non-pressurized reservoir. The expansion tank is the main refill point, while the reservoir only needs minor top-ups.
You can find the radiator right in front of the engine. The reservoir or expansion tank is typically on the right side. It’s a translucent-white container with a lid marked “Caution Hot”.
If you’re having trouble locating either, check your owner’s manual.
Step 3: Inspect the Coolant Level in the Radiator and Reservoir
If your radiator has a cap, check that it’s full. For cars with no radiator pressure cap, skip this step and check the overflow or expansion tank instead.
A coolant tank will have Min and Max lines. If the coolant level is below the Min line, you’ll need to top it up. Also, check the coolant color. Regular coolant should be clear and match the color of fresh coolant. If it’s dark or sludgy, schedule a coolant flush with your mechanic.
NOTE: Only proceed if the coolant level is low and the coolant doesn’t appear contaminated or too old. Contact your mechanic immediately if you suspect a leak or broken radiator hose is causing the low coolant level.
Step 4: Prepare the Coolant Mixture (Optional)
Premixed coolant (50% water) is available at most stores, but you can get undiluted antifreeze and mix it yourself.
If you do, remember to:
- Use the correct coolant type for your car.
- Follow the manufacturer’s dilution instructions.
- Only use distilled water, not filtered or tap water.
- Seal and store excess coolant or antifreeze properly.
Now that the coolant mixture is ready, it’s time to pour it in.
Step 5: Pour the Coolant into the Refill Points
Use a funnel to pour the fresh coolant into the refill points — the radiator (only if it has a cap), overflow tank, or expansion tank.
If you’re filling the radiator, pour until it is full. For the other tanks, aim for somewhere between the Min and Max lines. Overfilling can cause pressurization issues as the coolant expands when it’s hot.
Next, close all caps securely.
Step 6: Check for Air Pockets and Overheating
Close your hood and start your vehicle. Take a 30-minute drive with the heating on full. This brings the engine up to operating temperature and works any trapped air out of the cooling system, including the heater core.
If the drive goes well with no overheating, let the engine cool, then check if the coolant level has dropped as air escapes. Top up and test until the level stays consistent.
If the temperature gauge spikes or the car engine overheats during the drive, stop immediately and turn off the engine. Don’t open the hood right away, as it could release hot steam. This indicates an underlying coolant system problem. Get it checked by a professional.
Next, let’s learn the warning signs and possible future impact of driving with low coolant.
What Happens When You Drive with Low Coolant?
Your car will still run with the engine coolant level below the minimum, but you risk serious engine damage the longer you drive. You can get by with frequent top-ups, but it’s better to promptly fix the cause.
The symptoms of extremely low coolant levels include, but aren’t limited to:
- Heater blowing cold or lukewarm air (not enough hot coolant reaching the heater core)
- Unusually high temperature gauge readings due to engine overheating
- Knocking or gurgling noises from the engine compartment (the radiator gets filled with air due to very low coolant)
- Sweet-smelling steam from the engine (indicates coolant leaking onto hot engine components)
If any of these happen, immediately find a safe parking place and shut off the engine. Contact your mechanic and schedule car maintenance.
Constantly finding your coolant level too low?
There’s probably an underlying issue worth investigating.
Why Your Coolant Level Keeps Dropping
If your coolant level keeps dropping repeatedly, simply topping it off may not solve the real problem.
Common causes of ongoing coolant loss include:
- Cooling system leaks: A damaged radiator hose, cracked coolant tank, loose clamps, or radiator leaks can slowly reduce coolant levels over time.
- Faulty pressure caps: A worn pressure cap may fail to maintain proper pressure, allowing coolant to escape.
- Water pump problems: A failing water pump can leak coolant or reduce its circulation through the engine.
- Evaporation from overheating: Repeated overheating can cause water in the coolant to evaporate, gradually lowering the level.
- Cracked heater core: Cracks in the heater core can cause coolant to leak into the cabin. Look for dampness, a sweet smell, or a steamy, oily windshield.
- Engine bay leaks: In severe cases, coolant may leak internally with no visible puddle. This can be due to a blown head gasket, cracked cylinder head, or cracked engine block. You may notice sweet-smelling exhaust smoke, milky or foamy oil on the dipstick, or unexplained coolant loss.
Address cooling system problems promptly to avoid worsening engine damage.
Now, remember how we mentioned getting the right type of coolant before refilling the tank?
Let’s see what they are.
How to Choose the Right Coolant for Your Car
There are several different coolant types available, and you need to pick the one that works for your car’s engine.
To find the right coolant type for your car’s engine, you can check:
- The owner’s manual
- The manufacturer’s website (if it has a VIN lookup)
- The pressure cap at the refill point
Here’s an overview of the three main types of radiator fluid:
| Coolant Type | Composition | Type of Vehicle | Common Colors |
| Inorganic Additive Technology (IAT) | Made with ethylene glycol, phosphates, and silicates | Mostly older cars | Bright green |
| Organic Acid Technology (OAT) | Contains corrosion inhibitors instead of phosphates and silicates | Most modern American vehicles, especially GM | Orange, red, or purple |
| Hybrid Organic Acid Technology (HOAT) | Combines organic acids with silicates or phosphates | Usually European and Asian cars | Orange or yellow |
Lastly, choosing between premixed and concentrated coolant is a matter of preference. Premixed coolant is safe and convenient, but less cost-effective. Meanwhile, concentrated coolant is more affordable and can be mixed in a custom ratio for different climates. However, it requires the correct ratio and distilled water (not tap water).
Answers to some FAQs are up next.
5 FAQs on Engine Coolant
Here are the answers to some common questions on engine coolant to help you understand better:
Although the terms are often used interchangeably, they aren’t the same.
Coolant, also called radiator fluid, is a mixture of antifreeze, water, and additives like corrosion inhibitors. It circulates through the system to keep your engine temperature stable.
Meanwhile, antifreeze is the concentrated chemical component of coolant (minus the water), typically made from ethylene glycol or propylene glycol. It raises the boiling point and lowers the freezing point of the coolant mixture.
You shouldn’t, especially not as a long-term substitute for proper coolant. Water lacks the properties to protect against freezing, boiling, and corrosion.
In an emergency, when water is your only option, it can help you manage an overheating engine until you reach a safe stopping point.
Remember that non-distilled water contains minerals and contaminants that can damage your car engine, making a cooling system flush necessary. Distilled water is always a better option, even in an emergency.
A safe engine temperature should be between 160°F and 225°F. Driving outside this operating temperature range risks engine damage.
Overheating could lead to engine knocking, increased fuel consumption, cylinder head damage, and head gasket failure. Meanwhile, a cold-running engine faces issues with performance, acceleration, and stalling.
Most manufacturers recommend a coolant flush every 30,000 to 70,000 miles. However, if the coolant in the reservoir appears very dark, has metal specks, or looks sludgy, schedule a coolant change sooner.
Mixing different coolant types or adding the wrong coolant type will impair performance. Mixing coolants can cause their additives to react, leading to corrosion of the radiator and other engine block components.
Simplify Coolant Maintenance with AutoNation Mobile Service
Adding coolant to the engine is an important car maintenance procedure. Ensuring your car has enough coolant can help prevent overheating and other related issues.
However, if your coolant looks dirty or you suspect a coolant leak, take care of it the convenient way with AutoNation Mobile Service!
We’re a mobile auto repair service you can book online to have professionals come to your driveway for all your maintenance and repair needs. We’re available 7 days a week and offer a 12-month/12,000-mile warranty on every repair to ensure it’s done right.
Contact us today to get your coolant replaced or fix any cooling system issue, and we’ll send our best mechanics to help you out.