How to Put Coolant in Your Car: A Complete 10 Step Guide

Putting coolant in your car is an essential maintenance task that every car owner should know how to do properly.

Filling up the coolant ensures your engine does not overheat while driving.

Key Takeaways:

  • Let the engine fully cool before attempting to open the radiator cap or coolant reservoir. Hot pressurized coolant can cause severe burns.
  • Locate the radiator cap or coolant reservoir, usually in the front of the engine bay.
  • Use a 50/50 mixture of distilled water and engine-compatible antifreeze. Check your owner’s manual.
  • Add coolant slowly through the reservoir, not directly into the radiator.
  • Replace the radiator cap and run the engine to test for overheating.
  • Retop off coolant levels once the system cools again. Check for leaks.
  • Flush old coolant and change every 30K-50K miles for optimum performance.
  • Use the correct coolant type to avoid engine damage. Mixing coolants can cause sludge.
  • Improper disposal of coolant is hazardous to the environment. Drop it off at disposal sites.

The cooling system in your car works to prevent the engine from overheating while in operation. It uses a special blue or green fluid called engine coolant that flows through passages in the engine block and cylinder head, absorbing excess heat.

The heated coolant then makes its way to the radiator where it is cooled before returning back to the engine, completing the cycle. Maintaining proper coolant levels is therefore critical to engine health.

Running low on coolant can lead to catastrophic overheating issues and cause expensive damage to engine components.

That is why it is important for all car owners to know how to periodically check coolant levels and top it up correctly.

How to Put Coolant in Car (10 Steps)

Step 1: Let the Engine Cool Completely

The very first step is to make sure your car’s engine has had sufficient time to cool down completely after driving it.

Attempting to open the radiator cap or coolant reservoir while the engine is still hot can be extremely dangerous. When hot, the coolant system is under high pressure.

Opening the cap too soon can lead to hot coolant spewing out forcefully, which could cause severe scalding. Always allow adequate cooling time first.

Turn off your engine and let it sit for at least 30 minutes before checking coolant levels. If you have been driving for an extended time or at high speeds, allow up to an hour of cooling time.

The best way to check if the system has cooled is to touch the radiator cap or upper radiator hose. They should be cool enough to touch without burning your hand.

As an added precaution, cover the radiator cap with a thick rag when opening it. This will protect you if any residual pressure remains. Better to be safe than sorry!

Step 2: Locate the Radiator Cap or Coolant Reservoir

Modern vehicles have a plastic coolant reservoir or expansion tank. Older models will have the radiator cap directly on top of the radiator. Locating this is your next step.

The coolant reservoir is usually made of translucent plastic and sits somewhere in the front engine bay near the radiator. It has a MIN and MAX mark labeled on the side to indicate proper fill levels.

If your car has no reservoir, look for the radiator cap on top of the radiator. It is typically a pressure cap that you have to push down and turn to unlock.

Check your owner’s manual if you have difficulty finding the exact location. Some cars may have the reservoir or radiator cap hidden from plain view.

Step 3: Remove the Radiator Cap or Reservoir Lid

Once located, you can now open the radiator cap or unscrew the coolant reservoir lid. Turn it counterclockwise to open.

Place a thick rag over the cap and apply downward pressure while turning it. This allows any leftover vapor pressure to escape gradually. Never open it abruptly.

For plastic reservoir lids, use your fingers to turn it counterclockwise and unscrew it. Be aware that the interior of the reservoir will be hot so proceed with care.

Set both caps aside in a secure place to avoid losing or misplacing them. You will need to replace them properly after refilling the coolant.

Step 4: Drain the Old Coolant (Optional)

Refilling the coolant is typically all that is needed if your levels are just low. However, for severely contaminated or old coolant, doing a complete drain and flush is recommended.

Here are the steps to drain out all old engine coolant:

  • Use jack stands to safely raise the front of the car. Position a large drain pan underneath.
  • Locate the radiator drain plug, usually at the bottom corner. Place a pan and turn counterclockwise to open.
  • Fluid will begin draining out. Allow it to fully drain until the radiator is empty.
  • Also disconnect the lower radiator hose at the clamp to help it drain completely.
  • Once drained, reattach the lower hose and close the drain plug by turning clockwise.
  • Dispose of the old coolant properly. Most auto parts stores will collect it.
  • Lower the vehicle back down once finished.

Now you are ready to refill the system with fresh coolant.

Step 5: Mix the Coolant with Distilled Water

Engine coolant is typically a concentrated antifreeze fluid that needs to be diluted 50/50 with distilled water before adding to your car.

The antifreeze ingredient (usually ethylene glycol) provides freezing and boiling protection. The water helps absorb more engine heat.

Mixing concentrated coolant with distilled water is recommended for optimal performance and protection.

Never use plain tap water, which contains minerals that can leave deposits inside the cooling system over time.

Follow the directions on your particular coolant’s container to mix it correctly. Most are a simple 50/50 ratio with distilled water.

Shake the jug well after mixing to fully incorporate the antifreeze and water. Now you have your diluted engine coolant ready for pouring into the radiator or reservoir.

Step 6: Add the Coolant

With your pre-mixed coolant in hand, you can now refill the system. Slowly pour it into the coolant reservoir using a funnel.

If your vehicle does not have a reservoir, carefully pour the coolant into the radiator opening itself. Add just enough that levels reach the very top.

On the reservoir, fill up to the MAX line on the side. Avoid overfilling past the full mark.

Adding coolant through the reservoir rather than directly into the radiator is the proper method. This ensures no air pockets get trapped inside the system.

Go slowly to avoid spills. Coolant stains and can irritate skin, so wear gloves and eye protection when handling.

Reinstall the reservoir cap or radiator cap once finished adding fluid. Turn clockwise until snug.

Step 7: Replace Thermostat and Hoses (Recommended)

Although optional, it is smart to replace your engine’s thermostat and radiator hoses when refilling the coolant.

The thermostat is a temperature-controlled valve that opens and closes to regulate coolant flow. A stuck thermostat is a common cause of overheating failures. Replacing yours ensures proper temperature regulation.

Inspecting radiator hoses for cracks, swelling, or brittleness is also advised. Worn hoses can burst under pressure. Take the opportunity to replace damaged hoses.

Doing this extra maintenance helps guarantee your freshly filled cooling system performs reliably for the long haul.

Step 8: Run Engine and Test for Overheating

After filling up the coolant, the next step is to start the car and monitor engine temperature.

Let the engine idle for several minutes. Turn on the heater and check that heat starts blowing from the vents once warmed up.

Keep an eye on your temperature gauge. It should show a steady reading right in the middle of the range. No spikes.

Take the car for a short drive, about 10 minutes minimum. Keep observing the temperature gauge and heater performance during the drive.

If you notice the needle creeping too high, pull over and shut off the engine immediately. Allow it to fully cool before inspecting for leaks or issues.

Step 9: Recheck Coolant Levels When Cooled

After running and testing the engine, park your car and give it adequate time to cool back down completely.

Then check the coolant level again through the reservoir or radiator filler neck. It may have dropped slightly after circulation.

Top it back up to the MAX fill line if needed. Only re-add coolant when the system has fully cooled to prevent burns or damage.

Getting the level perfect at this point ensures you have bled out any trapped air and filled the system fully.

Step 10: Inspect for Leaks

The final step is to check for any coolant leaks around the engine bay or underneath the car.

Look for wetness, drips, or green fluid stains that would indicate a leak from the hoses, radiator, water pump, or other components.

Catching leaks now prevents bigger problems down the road. Wet spots often mean you have a failing coolant hose, water pump seal, or gasket issue.

Take note of any leaks and have them repaired as soon as possible by a certified auto technician. Neglecting leaks can lead to coolant depletion and overheating.

And that concludes the full process for adding coolant to your vehicle! Following these 10 key steps properly ensures your engine stays running cool for the long haul.

Different Types of Engine Coolant

When refilling your coolant, it is essential to use the specific type recommended by your vehicle manufacturer. Pouring in the wrong coolant type can cause sludge buildup and corrosion inside the engine.

Here are the main coolant types you will encounter:

  • Green – Conventional ethylene glycol antifreeze that includes silicate corrosion inhibitors. Used in many Asian and European cars.
  • Yellow/Orange – Organic acid technology (OAT) coolant that usually lasts longer. Common in newer GM and Volkswagen vehicles.
  • Red – Hybrid OAT formula approved for use in most Ford and Chrysler vehicles. Contains both organic and inorganic acids.
  • Blue – Phosphate-free OAT coolant that protects aluminum engine parts. Used in high-end makes like Audi, BMW, and Mercedes.
  • Purple – Hybrid OAT coolant containing silicates but no phosphates. Compatible with certain luxury brands.

Always check your owner’s manual for the exact coolant type specified by the manufacturer. Mixing incompatible coolants often creates a thick sludge that can block coolant channels and lead to overheating or corrosion damage.

When in doubt, stick to filling up with the same color already present in your cooling system. Never mix colors unless approved.

Signs of Low Coolant

Watch for these warning signs that your vehicle may be running dangerously low on coolant:

  • Engine temperature gauge needle creeping into the red zone
  • Heater blowing cold air or taking too long to warm up
  • Sweet, sickly coolant smell from the engine bay
  • Visible coolant leaks under the car
  • White smoke from the exhaust pipe
  • Bubbles in the coolant reservoir or radiator
  • Loose or ruptured hoses caused by overheating
  • Reduced heat protection and repeated overheating

Do not ignore these symptoms. Safely pull over and switch off the engine if you notice any while driving. Low coolant can lead to catastrophic engine damage if the overheating is not addressed promptly.

When to Change the Coolant

While occasional top-offs are needed, you should also drain and refresh the entire coolant system every few years. Here are some guidelines on when to do a complete fluid change:

  • Every 30,000 to 50,000 miles – For most vehicles under normal operating conditions, coolant should be flushed and replaced around this mileage interval. Some may go slightly longer between changes.
  • Every 2-3 years – Even if mileage is low, coolant should still be refreshed every few years at a minimum. Antifreeze additives can break down over time.
  • When switching coolant colors/types – Drain old fluid if switching to a different coolant composition required by your vehicle manufacturer. Do not mix incompatible coolants.
  • After major engine repairs – Flush out old contaminated coolant lingering after repairs like head gasket or water pump replacements.

Refer to your owner’s manual maintenance schedule for the ideal coolant change intervals. Severe driving conditions may necessitate more frequent flushing.

Coolant Safety Tips

Here are some important safety precautions when handling engine coolant:

  • Wear gloves and eye protection when handling. Ethylene glycol is toxic if ingested.
  • Avoid skin contact. Coolant can irritate and damage skin tissue. Rinse immediately if any gets on you.
  • Store new and used coolant bottles securely away from pets and children.
  • Only pour down approved drains. Disposing improperly can contaminate groundwater.
  • Recycle old coolant properly. Most auto parts stores accept it.
  • Work in a well-ventilated area. Inhaling coolant vapors is hazardous.
  • Never remove the radiator cap until fully cooled to avoid scalding.
  • Keep coolant bottles sealed when not in use to inhibit evaporation and limit exposure.

Exercising proper care and precautions will keep you safe when servicing your vehicle’s cooling system.


Maintaining proper coolant levels is vital for engine health and preventing catastrophic overheating damage. All car owners should be familiar with how to periodically check coolant and top it up when running low.

Following this comprehensive 10-step guide will walk you through the process of adding coolant to your car’s radiator or reservoir tank safely and correctly.

Allowing adequate engine cool down time, using the proper 50/50 coolant mix, bleeding trapped air from the system, testing for leaks, and exercising good safety practices are all key steps outlined.

Equipped with this knowledge, you can keep your engine running cool for many more carefree miles on the road. Ignoring low coolant warnings can lead to expensive repairs down the line.

Be sure to use the exact coolant type specified by your manufacturer and change it every 30K-50K miles for optimal corrosion protection and performance. Now go check those levels!

Frequently Asked Questions

1. How often should you check the engine coolant?

Check coolant levels at least once a month when doing routine engine oil checks. Top it up if the reservoir is low. Also inspect levels before any long trip.

2. What color should the coolant be?

Coolant color varies based on composition. Most are green, yellow/orange, red, or blue. Avoid mixing different colors. Use what is specified for your vehicle.

3. Is it bad to mix different types of coolant?

Yes, only mix coolants if specifically approved by your manufacturer. Mixing incompatible types creates sludge that can clog the radiator and lead to overheating.

4. Can you use water as engine coolant?

Water alone boils too easily. Always mix it 50/50 with antifreeze for proper protection. Distilled water is preferred as it lacks contaminating minerals.

5. Do you have to run the engine after adding coolant?

Yes, idling the engine and taking it for a short drive checks for leaks and bleeds out air pockets. Monitor temperature gauges for signs of overheating.

6. How do you know if your coolant is low?

Top signs are overheating, heater issues, coolant leaks, sweet smell, white exhaust smoke, and the reservoir level being below the MIN mark.

7. What could happen if the coolant reservoir cap is left open?

Leaving the cap loose or open allows coolant to evaporate over time and also inhibits the system from properly pressurizing to raise the boiling point.

8. Is it better to add coolant to a hot or cold engine?

Only add coolant when the system is fully cool to prevent scalding injuries or damage from adding fluid to extremely hot metal components.

9. Can I drive my car if the coolant is a little low?

Exercise extreme caution. Top it up as soon as possible to safe levels. Repeated driving while critically low can lead to catastrophic overheating.

10. Does coolant expire or go bad over time?

Yes, the corrosion inhibitors in antifreeze break down after several years. Flush old contaminated coolant and replace with fresh fluid as recommended.

Leave a Comment