Where to Put Coolant in Your Car

You add coolant to the translucent plastic reservoir in the engine bay labeled “coolant” or marked with a thermometer symbol; do this only when the engine is completely cold and fill to the “FULL” or “MAX” line. On some older vehicles with a radiator cap, you can also fill the radiator itself—but only when cold. Details vary by make and model (and hybrids/EVs may have multiple coolant circuits), so always confirm the procedure in your owner’s manual.

Finding the Coolant Reservoir

The coolant reservoir—also called an expansion or overflow tank—is usually a translucent plastic bottle near the radiator or one of the front corners of the engine bay. It typically has molded level marks (“MIN” and “MAX”) and a cap labeled “engine coolant,” “coolant,” or a symbol of a thermometer in liquid. You don’t need to open the radiator cap for routine top-ups on most modern cars; the reservoir is the proper fill point.

Exceptions: Radiator Caps and EV/Hybrid Cooling Systems

Some older vehicles have a metal radiator cap in addition to (or instead of) an expansion tank. Only remove this cap when the engine is stone cold—hot systems are pressurized and can spray scalding coolant. Electric and hybrid vehicles often have separate, labeled reservoirs for battery, inverter, and cabin heating circuits; each system may have its own specific coolant and fill procedure, so consult the manual or a dealer service guide.

How to Check and Top Up Coolant Safely

The following steps outline a safe, general procedure to check and top up the coolant in most vehicles. Always adapt to the instructions in your owner’s manual if they differ.

1. Park on level ground and let the engine cool fully. The upper radiator hose should be cool to the touch; this often means waiting several hours after driving.
2. Locate the coolant reservoir. Identify the “MIN” and “MAX” marks on the side of the tank.
3. Check the level without opening the cap. If the coolant sits between MIN and MAX, no top-up is needed. If it’s at or below MIN, add coolant.
4. Select the correct coolant. Use the exact type specified in your owner’s manual (e.g., Dex-Cool/OAT, HOAT, P-HOAT, G12evo, Toyota SLLC, Honda Type 2). Do not rely on color alone, and avoid mixing types. If you’re unsure, ask a parts counter with your VIN. In a true emergency, you may add a small amount of distilled water to reach MIN, then have the system serviced promptly.
5. Use the right mixture. Most cars require a 50/50 mix of antifreeze and distilled water; many products are sold pre-mixed. If using concentrate, dilute with distilled water per the label.
6. Open the reservoir cap slowly. With the engine cold, crack the cap carefully to release any residual pressure. Use a rag and eye protection.
7. Add coolant using a clean funnel. Pour slowly until the level reaches the MAX line; avoid overfilling.
8. Reinstall the cap tightly. Wipe any spills; coolant is slippery and toxic to pets.
9. Run the engine and monitor. Start the car, set the heater to HOT with the fan on low, and watch for leaks and normal temperature readings. After a short drive and a complete cool-down, recheck the level and top up if needed.

These steps cover routine top-ups. If you repeatedly find the level low, or the engine runs hot, you likely have a leak or another cooling-system issue that needs professional diagnosis.

Coolant Types and Compatibility

Automakers specify different coolant chemistries (IAT, OAT/Dex-Cool, HOAT, P-HOAT, Si-OAT, and others) tailored to engine materials and service life. The color is not a reliable guide. Mixing incompatible coolants can cause sludge, corrosion, or overheating. Use the product that meets the exact specification in your manual (often listed under “coolant” or “antifreeze”) and, when diluting, use distilled water to prevent mineral deposits. Common intervals range from about 5 years/100,000 miles for many modern OAT coolants to 2–3 years for older IAT types, but follow your vehicle’s maintenance schedule.

Warning Signs and When to See a Mechanic

The following indicators can help you decide when it’s time for professional attention rather than a simple top-up.

• Frequent low coolant level, visible drips, or colored crust around hoses, radiator, water pump, or reservoir
• Sweet smell in the cabin, fogged windows, or damp front carpets (possible heater core leak)
• Overheating, fluctuating temperature gauge, or a “high coolant temp” warning
• No cabin heat at idle but heat while driving (possible air in system or low coolant)
• White steam from the exhaust after warm-up, milky oil, or oily film in the reservoir (possible internal leak)
• Cooling fan running constantly or trouble codes related to coolant temperature

Any of these symptoms suggests a leak, air intrusion, or component failure. Continuing to drive an overheating vehicle risks severe engine damage—stop safely and seek service.

Frequently Asked Questions

These quick answers address common concerns drivers have about coolant and topping up.

• Is coolant the same as antifreeze? Antifreeze is the concentrate; coolant is antifreeze mixed with water (usually 50/50).
• Can I add water only? In an emergency only, and use distilled water. Restore the correct coolant mix as soon as possible to maintain corrosion and freeze/boil protection.
• Do I need to bleed the system? Many cars self-bleed via the reservoir. Others have bleeder screws or specific procedures; air pockets can cause overheating or no heat. Check your manual.
• How often should I change coolant? Follow the factory schedule—commonly 5 years/100,000–150,000 miles for long-life coolants, shorter for older formulations.
• What color should coolant be? Colors vary by brand and chemistry; don’t choose by color. Match the spec in your manual.

When in doubt, verify the correct coolant specification for your VIN and follow the manufacturer’s fill and bleed procedure to avoid costly mistakes.

Summary

Fill coolant at the marked reservoir—only with the engine cold—and up to the MAX line using the exact coolant type your manufacturer specifies. Avoid mixing formulations, watch for signs of leaks or overheating, and consult your owner’s manual for vehicle-specific steps (especially for older cars with radiator caps or hybrids/EVs with multiple loops). If low levels persist or temperatures spike, seek professional service promptly.

Can I refill coolant myself?

Yes, you can refill your car’s coolant yourself, but you must use the correct type of coolant and follow the proper safety steps, including waiting for the engine to be completely cold. Locate the coolant reservoir or radiator cap, identify the correct fluid type from your owner’s manual, and add the coolant to the indicated fill line on the reservoir. Never mix different types of coolants, as this can cause damage. 
Safety First

1. Ensure the engine is cold: before opening the coolant system. Opening a hot system can release pressurized, hot fluid, leading to severe burns. 
2. Locate the coolant reservoir or radiator cap: under the hood. 
3. Use the correct coolant: by checking your owner’s manual for the specific type recommended for your vehicle. 

Steps to Refill Coolant

1. Find the fill line: on the coolant reservoir. Most reservoirs have “min” and “max” or “cold” and “hot” fill lines. 
2. Add the appropriate coolant: to the reservoir. 
   • You can use a pre-mixed 50/50 solution of coolant and distilled water, or mix your own if using concentrated coolant. 
   • Ensure the fluid level reaches the “cold” or “min” line. 
3. Replace the cap securely . 

Important Considerations

• Don’t overfill: Coolant expands when hot, so overfilling can cause hoses or the reservoir to burst. 
• Watch for leaks: If the coolant level drops again, you may have a leak that needs professional attention. 
• Dispose of old coolant responsibly: Take used coolant to an auto parts store or recycling center for proper disposal, as it is toxic. 

Is coolant the same as antifreeze?

No, antifreeze and coolant are not technically the same, though the terms are often used interchangeably. Antifreeze is a concentrated chemical, typically ethylene or propylene glycol, which must be mixed with water to become coolant, the complete fluid used in a vehicle’s cooling system. The coolant mixture provides both freeze protection from the antifreeze and heat transfer properties from the water, along with corrosion inhibitors. 
Antifreeze

• What it is: A concentrated liquid chemical, such as ethylene glycol, that serves as the primary ingredient in coolant. 
• What it does: Lowers the freezing point of water and raises its boiling point, protecting the engine from both freezing in cold weather and overheating in hot weather. It also contains additives that inhibit corrosion. 

Coolant

• What it is: A mixture of antifreeze (glycol) and water, typically a 50/50 ratio, that is put into the radiator. 
• What it does: Transfers heat away from the engine to prevent overheating and circulates through the cooling system. 

In summary:

• All antifreeze is a type of coolant, but not all coolant contains antifreeze (though in automotive contexts, it almost always does). 
• You can buy concentrated antifreeze, which you then mix with distilled water, or you can buy premixed coolant, which is already in the proper solution. 

Do you add coolant to the reservoir or radiator?

You should add coolant to the radiator in systems with a radiator cap and no expansion tank, but add it to the coolant reservoir in systems with a separate reservoir and a radiator with a simple, non-pressure cap. Always ensure the engine is completely cool before opening either cap to avoid serious injury from hot, pressurized coolant. 
This video explains how to check and add coolant, including identifying the type of system you have: 55sBackyard ChevyYouTube · Nov 27, 2021
Systems with a Reservoir (Expansion Tank)

1. 1. Locate the reservoir: This is the plastic tank, often with high and low level markings, that is separate from the radiator. 
2. 2. Remove the reservoir cap: Wait until the engine is cold to release any residual pressure. 
3. 3. Add coolant: Pour the correct coolant (pre-mixed or concentrated with distilled water) into the reservoir until it reaches the “cold fill” or “max” line. 
4. 4. Start the engine: Once the engine is running and warms up, the coolant level in the reservoir may drop. If it does, top it off to the “full” line while the engine is running. 

Systems with a Radiator Cap Only

1. 1. Remove the radiator cap: Opens in new tabEnsure the engine is cold to avoid injury. Use a rag to cover the cap as a safety precaution when loosening it. 
2. 2. Add coolant: Opens in new tabPour the appropriate coolant directly into the radiator until it is completely filled. 
3. 3. Start the engine: Opens in new tabLet the engine run until the thermostat opens, and then top off the radiator again as needed. 

How to top up coolant?

To top up engine coolant, first, wait for the engine to cool completely. Locate the coolant reservoir and check the fill lines for “COLD” or “MAX”. Slowly open the reservoir cap to release any pressure. Add the correct, pre-mixed or concentrated coolant from your owner’s manual to the appropriate fill line. Replace the cap securely and check your manual for a proper cap seal, and repeat as needed after the engine warms up. 
Step-by-Step Guide

1. 1. Ensure Safety: Make sure your vehicle is parked on a level surface and the engine is completely cool. 
2. 2. Locate the Reservoir: Find the translucent plastic coolant expansion tank, usually under the hood. 
3. 3. Release Pressure: Carefully and slowly open the reservoir cap to release any built-up pressure. A rag can be helpful for safety. 
4. 4. Check the Level: Look for the “FULL” and “LOW” or “COLD” and “MAX” markings on the reservoir. 
5. 5. Add Coolant: If the level is below the “COLD” or “MINIMUM” line, add the correct coolant. 
   • Check your owner’s manual: for the specific type and mixture (e.g., 50/50) required for your vehicle. 
   • Never mix different coolant types: unless the universal type is specifically listed as compatible. 
   • You can pour the fluid directly from the bottle or use a funnel. 
6. 6. Replace the Cap: Securely replace and tighten the cap by twisting it clockwise. 
7. 7. Monitor the Level: After the engine warms up, the level may drop as air is pushed out of the system. Top off again as needed until the level stabilizes at the appropriate line. 

Important Reminders

• Use the correct coolant type: Mixing coolants can cause engine damage. 
• Don’t use tap water: Distilled water is best when mixing concentrated coolants to prevent deposits. 
• Look for a leak: If you frequently need to top off coolant, it might indicate a leak that requires professional inspection.