How do I know if my car is low on coolant?

When coolant is running low, you may see warning lights, notice the temperature rising, or find the level is low in the expansion tank after a cold start. Quick checks and signs can help you catch a problem before it causes engine damage.

Dashboard signals and engine behavior to watch

These on-board indicators and symptoms are common early warnings that your cooling system may be low on coolant or otherwise troubled:

• The temperature gauge climbs toward the red or a high-temperature warning light appears.


• A coolant warning light illuminates on the dashboard.


• The cooling fans run more often or stay on longer than usual.


• You see steam or a sweet-smelling vapor coming from under the hood.


• The heater inside the cabin provides little or no warm air.


• You notice a puddle or damp area under the front of the car, especially near the radiator or hoses.

If you encounter any of these signs, pull over safely as soon as possible and plan to check the coolant level once the engine has cooled. Ignoring them can lead to overheating and costly damage.

How to safely check the coolant level

Follow these steps to verify the level when the engine is cold and avoid burns or pressure-related injuries:

• Park on level ground and turn off the engine. Allow it to cool completely before opening any caps.


• Open the hood and locate the translucent expansion or radiator reservoir, which has “MIN” and “MAX” indicators.


• Look at the coolant level in the reservoir. It should be between the MIN and MAX marks. If it’s near or below MIN, the system is likely low.


• Do not open the radiator cap when the engine is hot. If you need to top up, use the expansion tank cap only, unless your manual instructs a separate radiator-cap procedure.


• Use the correct coolant type for your vehicle (check the owner's manual). Most cars use a 50/50 mix of coolant and distilled water, unless you buy pre-mixed coolant.


• If you need to top up, add coolant gradually and do not overfill beyond the MAX mark. After topping off, replace the cap securely and run the engine to operating temperature, then recheck when cool.

If you’re unsure about the correct type or method, or if the level doesn’t stay at the proper mark after topping up, contact a professional. A persistent drop in level often signals a leak or another issue in the cooling system.

What to do if you notice a leak or overheating

Act quickly to minimize engine damage and identify the source of the problem:

• If the engine is overheating, stop driving as soon as it is safe and allow the vehicle to cool before inspecting further.


• Look for visible leaks under the car, around hoses, the radiator, the water pump, and the expansion tank. A sweet smell or white/green fluid can indicate coolant leakage.


• Do not continue driving with a low coolant level. Top off only with the correct coolant type if you know it, and do so with the engine cooled.


• If you cannot locate a leak or the engine continues to overheat, arrange professional service. A pressure test can help pinpoint leaks and a cooling-system service may be required.

Common underlying causes of coolant loss include worn hoses, a failed radiator cap, a breached radiator, a faulty water pump, or, in rare cases, head-gasket issues. A technician can diagnose and repair the root cause, and replace or flush the coolant as needed.

Additional notes on coolant care

To maintain optimal cooling system performance, follow these best practices:

• Check coolant levels regularly, especially before long trips or hot weather.


• Use the coolant type recommended by your vehicle manufacturer; do not mix types unless your manual allows it, and never mix different brands in a single system unless specified.


• Replace coolant according to the schedule in your owner’s manual, typically every 5–10 years or 100,000–150,000 miles for many modern formulations, though intervals vary by coolant type and vehicle use.


• Inspect hoses and the radiator for cracks, bulges, or signs of wear, and replace as needed.


• Keep the system clean and free of debris; a professional flush may be needed if corrosion or sludge builds up.

Regular maintenance helps prevent unexpected cooling-system failures and keeps your engine operating within its optimal temperature range.

Summary

Knowing when your car is low on coolant hinges on watching the dashboard indicators, listening to changes in engine temperature behavior, and performing a safe, cold-state check of the expansion tank level. If you find the level is low or you notice signs of leaks or overheating, top off with the correct coolant type if you can do so safely and seek professional inspection for persistent or unclear issues. Regular maintenance, including correct coolant type and scheduled replacement, helps prevent overheating and protects your engine from damage.

What are the symptoms of low coolant?

Symptoms of low coolant include a dashboard warning light, a rising temperature gauge, and a poorly working heater. You may also notice a sweet smell, a visible coolant leak under your car, or steam from the engine. 
Warning indicators

• Dashboard warning light: A dedicated low coolant light or the "check engine" light may illuminate. 
• Rising temperature gauge: The temperature gauge will move toward the red "hot" zone. 
• Poor cabin heating: The heater may only blow cold air because there isn't enough coolant to heat the air in the cabin. 

Visual and auditory signs 

• Steam from the engine: You might see steam coming from under the hood, especially when the engine is hot. 
• Visible coolant leak: A puddle of colored fluid (often green, pink, or orange) under your car after it has been parked is a strong sign of a leak. 
• Bubbling sounds: You may hear bubbling sounds from the engine. 

Other signs

• Sweet smell: A sweet, chemical odor can indicate a coolant leak. 
• Engine performance issues: Low coolant can cause poor acceleration, rough idling, or engine misfires. 
• Reduced gas mileage: The engine may become less efficient if it's not cooling properly. 

If you notice any of these signs, it is important to have your vehicle checked by a professional to prevent severe engine damage.

Can I just add coolant to my car?

Loosen the reservoir cap just a little, then step back letting pressure release. Remove the cap completely. If the coolant level is low, add the correct coolant to the reservoir (not the radiator itself). You can use diluted coolant by itself, or a 50/50 mixture of concentrated coolant and distilled water.

Can coolant be low without a leak?

Yes, coolant can be low without a visible leak due to internal issues like a faulty head gasket or radiator cap, or it can be lost through small, evaporation-level leaks that are hard to spot. Other causes include a leaky heater core, a failing water pump, or even just normal evaporation over time. It is important to address low coolant immediately as it can lead to overheating and severe engine damage. 
Potential causes of coolant loss without visible leaks 
This video explains some common reasons for coolant loss without visible leaks: 59sAutomobile basic ideasYouTube · Oct 9, 2025

• Faulty radiator cap: A worn or incorrect radiator cap may not seal properly, allowing coolant to escape as vapor without forming puddles. 
• Internal head gasket leak: The gasket between the engine's head and block can fail, allowing coolant to leak internally into the combustion chamber or mix with the engine oil. 
  • Signs: White smoke from the exhaust or a milky, frothy appearance in the oil on the dipstick or oil cap. 
• Leaky heater core: The heater core is located inside the vehicle's cabin. A leak here can cause coolant loss without visible puddles under the car, but you may notice a sweet smell inside the cabin or wet floorboards. 
• Evaporation: While the coolant system is a sealed system, some minor evaporation can occur over time, especially if the system has a faulty cap that allows it. 
• Internal engine/component cracks: Less commonly, a crack in the engine block, cylinder head, or intake manifold can lead to an internal leak. 
• Failing water pump: The water pump can develop a slow leak from its shaft seal, where the coolant may be flung around and evaporate before it can be seen. 

What you can do
This video explains how to check for coolant leaks: 1mBudget MechanicYouTube · Oct 2, 2022

1. Check the radiator cap: Inspect the radiator cap for wear or damage. A faulty cap is a common and easy fix. 
2. Look for signs of an internal leak: Check for white smoke from the exhaust or milky oil. If you see these signs, stop driving the vehicle immediately and have it towed to a mechanic. 
3. Check the heater: Turn on your car's heater. If it doesn't blow warm air or you notice a sweet smell inside the car, the heater core may be leaking. 
4. Have a professional pressure test: A mechanic can perform a pressure test on the cooling system to find small or hard-to-find leaks that may not be visible under normal conditions. 

How do I know if my car needs coolant?

You can tell your car needs coolant if the temperature gauge is rising, a warning light comes on, the heater doesn't work, or you see a sweet-smelling, colored fluid leaking under your car. A quick way to check is to visually inspect the coolant reservoir when the engine is cold to see if the level is below the "low" or "cold fill" line. 
Warning signs

• Rising temperature gauge: A gauge that moves toward the hot or "H" zone, especially combined with steam from the engine, is a major red flag. 
• Dashboard warning lights: A low coolant or engine temperature warning light can illuminate before overheating occurs. 
• Poor heater performance: If the cabin heater is not blowing hot air, it could be due to low coolant levels. 
• Sweet smell: A sickly-sweet odor often indicates a coolant leak. This is a key sign because coolant is one of the few automotive fluids with this smell. 
• Visible leaks: Look for puddles of colored fluid (red, green, pink, or blue) under your car. It's different from the clear water that drips from an air conditioner. 

How to visually check the coolant level

1. Ensure the engine is cold: Never open the radiator cap on a hot engine, as it is under pressure and can cause serious burns. 
2. Locate the coolant reservoir: This is typically a translucent plastic tank, often with "min" and "max" or "low" and "full" marks on the side. You can find its location in your car's manual if you can't find it. 
3. Check the level: Compare the liquid level to the markings on the reservoir. If it's at or below the "low" line, you need to add more coolant. 

This video demonstrates how to check your car's coolant level: 59sIn Shot ProductionsYouTube · Jan 24, 2013