Can I top up coolant myself?

Yes. In many cars you can top up the coolant yourself, provided you use the correct coolant type and follow proper safety steps. This isn’t something you should do if you’re unsure about your vehicle’s requirements, but with the right guidance it is a routine maintenance task for many drivers.

What you need to know before you begin

Following a careful plan helps prevent burns, spills, and damage to the cooling system. Start by identifying whether your car uses a traditional open radiator with a cap or a sealed overflow reservoir, and locate the exact fill point specified by the manufacturer.

Follow these steps to safely top up coolant, reducing the risk of burns or damaging the cooling system.

1. Park on level ground and let the engine fully cool before touching anything in the cooling system.


2. Locate the correct fill point (the expansion tank for most modern cars; the radiator cap for some older models).


3. Check your owner's manual for the required coolant specification and the dilution ratio (pre-diluted 50/50 or concentrate to be mixed with distilled water).


4. Use distilled water if you’re diluting concentrate; avoid tap water to prevent mineral deposits.


5. Slowly add coolant until the level reaches the MAX line on the reservoir; do not overfill.


6. Replace the cap securely and start the engine with the heater set to hot. Run for several minutes to help purge any air pockets; monitor for leaks.


7. Shut off the engine and let it cool again, then recheck the level and top up if necessary.

Completing these steps helps maintain proper cooling performance and reduces the chance of overheating. Always recheck the level when the engine is cold and inspect for leaks after driving.

Choosing the right coolant

Using the right coolant protects metals inside the cooling system and provides proper freezing/boiling protection. Here’s how to choose correctly:

• Check the vehicle’s manual or the current coolant bottle for the exact specification (for example, Dex-Cool, HOAT, or OAT formulations) and the recommended concentration.


• Do not rely on color alone to identify coolant type; color can vary by brand and may not indicate compatibility.


• Avoid mixing different coolant types unless explicitly approved by the manufacturer. If you must top up with a different type, plan a complete system flush later.


• If in doubt, use a pre-mixed coolant that matches the OEM specification to minimize mistakes.

Choosing the correct coolant helps prevent corrosion, deposits, and overheating. Always follow the label and your owner's manual for the exact specification.

System types and topping approaches

Open radiator system

Older or performance-oriented vehicles may have an open radiator system with a radiator cap and an expansion tank. Topping up can involve filling the reservoir or, in some configurations, removing the radiator cap when the engine is cold.

Follow these steps:

1. Ensure the engine is completely cool and on a level surface.


2. Identify the fill point (expansion tank or radiator neck) and remove the cap only if it’s safe to do so.


3. Fill slowly using the correct coolant until the MAX line is reached on the reservoir.


4. Secure the cap, run the engine with the heater on, and monitor the level as air is purged.


5. Let the engine cool again and recheck the level; top up if needed.

In open-radiator systems, monitoring for leaks and ensuring the level remains stable after a drive is essential for long-term reliability.

Sealed cooling system / overflow reservoir

Most modern cars use a sealed system with an overflow reservoir. Topping up is typically done through the reservoir cap only when the engine is cool. Do not vent or open the system while hot.

Follow these steps:

1. Let the engine cool completely and locate the expansion/overflow reservoir.


2. Wipe the cap area and slowly relieve any residual pressure before opening the cap fully.


3. Check the coolant specification and fill with the recommended mixture up to the MAX line.


4. Secure the cap and start the engine briefly with the heater on; observe the level as the system cycles.


5. Allow the engine to cool and recheck the level, topping up if necessary.

If the coolant level remains low after topping up, there may be a leak or another issue requiring professional inspection.

Summary

Yes, you can usually top up coolant yourself, provided you use the correct coolant type, follow safety steps, and accurately monitor the level. If you’re unsure about the correct specification, if the system repeatedly loses coolant, or if you notice signs of a leak, seek professional assistance to prevent overheating and potential engine damage.

Can you add coolant without flushing?

Yes, you can add coolant without flushing the system, but it is best to only do this when topping off a system with clean coolant, or when replacing a component like a reservoir. Adding coolant to a system with old, contaminated, or mixed coolants should be avoided, as it can lead to problems like gelation, poor cooling performance, and future damage. 
This video demonstrates how to add coolant to a car without flushing the system: 1m2CarProsYouTube · Oct 6, 2016
When it's okay to add coolant without flushing

• Coolant is clean: If the coolant in the system is clean, has no signs of oil or contamination, and is at its regular service interval, you can add coolant to the reservoir. 
• Adding a small amount: If you are simply topping off a small amount of coolant because the level is low between the "full" and "add" marks, it is generally safe to do so. 
• Replacing a reservoir: If you are replacing a leaking reservoir and the coolant is still clean, you can drain the old coolant, replace the reservoir, and then refill the system with new coolant. 

This video shows how to add coolant to a car with a radiator cap: 1mBackyard ChevyYouTube · Nov 27, 2021
When you should not add coolant without flushing

• Contaminated coolant: If the old coolant is dirty, looks like it has oil in it, or has been contaminated in any way, you must flush the system before adding new coolant. 
• Mixing incompatible coolants: If you don't know what kind of coolant is in the system, or if you're using a different brand, you should perform a flush to avoid mixing incompatible formulas, which can cause gelling and damage. 
• Coolant is old: Coolant breaks down over time, losing its ability to protect the engine. You should flush and replace the coolant according to your vehicle's maintenance schedule, even if it looks clean. 

This video demonstrates how to add coolant to a car without mess and removes air pockets: 52sHardly Moving ProductionsYouTube · Aug 18, 2018
Before adding coolant

• Find the source of the leak: Coolant is not consumed, so a low level indicates a leak. Before adding more coolant, find and fix the leak to prevent further loss. 
• Check the coolant's condition: Look for signs of contamination, such as rust, oil, or debris. 
• Get the system checked: If you are frequently adding coolant, have a mechanic inspect the cooling system to ensure there are no major leaks or problems. 
• Use the right type: Always use the correct type of coolant for your vehicle to avoid compatibility issues. 

Can I pour new coolant over old coolant?

You shouldn't mix coolants, no. But it has already been mixed so it needs to be all flushed out and the correct coolant put in.

Can coolant just be topped up?

Yes, you can top up your coolant, but it's crucial to do it safely and with the correct type of coolant. Make sure the engine is completely cool before you begin. To do this, locate the coolant reservoir, check the level against the "full" or "max" line, and add the appropriate mixture of coolant and distilled water (usually a 50/50 mix) if it's low. 
This video demonstrates how to check and top up your car's coolant: 1m2CarProsYouTube · Oct 6, 2016
How to top up your coolant
This video shows where to pour coolant in a car: 1mCars SimplifiedYouTube · Nov 18, 2023

1. Wait for the engine to cool: Never open the cooling system when it's hot. Allow at least two hours, or preferably overnight, for the engine to cool down completely to avoid burns from pressure release. 
2. Locate the reservoir: Find the coolant reservoir, which is a translucent plastic tank under the hood with "min" and "max" or "cold" and "hot" lines on the side. 
3. Check the level: Look through the tank to see the current coolant level. If it's between the "cold" and "hot" or "min" and "max" lines, you do not need to add any. 
4. Add the correct coolant: If the level is low, carefully open the reservoir cap to release any residual pressure, then remove it completely. Slowly pour in the correct coolant mixture. It is best to use the 50/50 pre-mixed coolant or mix the concentrated coolant with distilled water yourself, as using plain water can lead to problems over time. 
5. Replace the cap: Securely replace the reservoir cap after you've added the coolant. 
6. Monitor the level: Keep an eye on the coolant level over the next few days. If it drops again, you may have a leak that needs to be addressed by a mechanic. 

Is it okay to drive with low coolant?

No, it is not okay to drive with low coolant; you should pull over and address the issue immediately to prevent severe and costly engine damage like warped engine parts or a blown head gasket. Driving with low coolant can cause the engine to overheat, leading to decreased performance, accelerated wear and tear, and potential engine seizure. If the low coolant light is on, pull over as soon as it is safe to do so and get your vehicle checked. 
This video explains the signs and symptoms of low coolant levels in a car: 57sHelpful DIYYouTube · Jun 23, 2021
Risks of driving with low coolant

• Overheating: Without enough coolant, the engine's temperature will rise rapidly, as the coolant can no longer absorb and dissipate the heat effectively. 
• Engine damage: Overheating can cause metal engine components, like the engine block and cylinder heads, to warp or crack. It can also damage the head gasket, which is an expensive repair. 
• System failure: The strain from low coolant can lead to premature failure of other cooling system parts, such as the water pump, radiator, and hoses. 
• Reduced performance: An overheating engine runs less efficiently, leading to a loss of power and potentially higher fuel consumption. 

What to do if you have low coolant

• Stop driving immediately: If the low coolant warning light comes on, pull over safely and turn off the engine. 
• Assess the situation: Check to see if the coolant reservoir is completely empty. If it is, you likely have a leak, and you should not attempt to drive further. 
• Add coolant if safe: If the vehicle is only slightly low, you may be able to temporarily add a 50/50 mix of coolant and water to get to a mechanic. If you don't have coolant, adding water can help in a pinch, but be aware that using only water can lead to overheating because it boils at a lower temperature than coolant. 
• Call for assistance: If you're unsure about the severity of the issue or if you can't get to a repair shop, call a tow truck to avoid causing significant damage.