How to fix high coolant temperature?

If your engine gauge spikes toward the red or you see a coolant warning, stop driving as soon as it’s safe, let the engine cool, and begin a basic check of the cooling system. This guide outlines immediate safety steps, common causes, and practical actions you can take—or know when to call a professional—to address high coolant temperature.

Immediate safety steps when overheating

Before attempting any inspection or repair, focus on safety and preventing further damage. The following actions cover what to do right away when the engine is running hot.

1. Safely pull over to a secure location and switch off the engine. If you’re in traffic, move to the shoulder or a safe spot as soon as you can.


2. Turn off the air conditioning and, if possible, turn the heater to the maximum setting to help pull heat away from the engine. Do not force the vehicle to keep running hot in traffic.


3. Do not open the radiator cap or the coolant reservoir while the engine is hot. Steam and pressurized coolant can cause severe burns. Wait at least 15–30 minutes for the system to cool before inspecting.


4. Check for obvious signs of trouble from outside the engine bay, such as leaks under the vehicle, cracked hoses, or a visibly damaged radiator cap.


5. If you must drive a short distance to a repair facility, drive slowly and gently, avoid idle-heavy stops, and monitor the temperature gauge closely. If it climbs again, stop and call for roadside assistance.

These steps are designed to minimize damage to the engine and cooling system while you assess the situation. After the vehicle has cooled, you can begin a more thorough check or seek professional help.

Common causes of high coolant temperature

Several issues can push coolant temperature higher than normal. The list below highlights the frequent culprits and how they affect cooling performance.

• Thermostat stuck closed: The thermostat fails to open, preventing coolant from circulating through the radiator.


• Radiator or coolant passages clogged: Debris or sediment reduces cooling efficiency, causing heat buildup.


• Cooling fan problems: Electric fans or fan belts may fail, reducing airflow through the radiator at idle or low speeds.


• Low coolant level or leaks: Inadequate coolant lowers the system’s ability to absorb heat and transfer it to the radiator.


• Water pump failure: A failing pump can’t move coolant effectively, leading to overheating.


• Faulty radiator cap or pressure loss: A bad cap can allow coolant to boil at a lower temperature and reduce system pressure.


• Air in the cooling system: Air pockets can impede coolant flow and heat transfer.


• Head gasket issue: A blown head gasket can cause coolant loss or contamination and abnormal engine temperatures.

Understanding these causes helps narrow down the most likely culprits based on symptoms, maintenance history, and whether the issue appears at idle, during acceleration, or after the engine warms up.

Diagnostics you can perform (safe DIY)

If you are comfortable with basic car maintenance, you can perform several non-invasive checks to identify potential problems. The following checks cover routine inspections and simple tests that don’t require specialized equipment.

1. Check coolant level when the engine is cool. Top up with the correct mix (usually 50/50 coolant and water) if levels are low, and identify any visible leaks.


2. Inspect hoses and clamps for cracks, bulges, or looseness. Replace damaged hoses or tighten clamps as needed.


3. Inspect the radiator cap for signs of wear or failure. Replace a faulty cap to restore proper system pressure.


4. Test fans and fan operation. Ensure electric fans engage when the engine warms up or when the AC is on. Check fuses and relays if the fans do not operate.


5. Look for air leaks or signs of air pockets in the cooling system. If air is suspected, the system may need to be burped or professionally bled to remove trapped air.


6. Check for external leaks or pooled coolant under the engine that could indicate a hose, radiator, or water pump issue.


7. Consider checking for diagnostic trouble codes (DTCs) with an OBD-II scanner. Codes related to the thermostat, temperature sensors, or cooling system can guide the next steps.

These checks can help you decide whether the problem is a simple, inexpensive fix or something that requires professional service. If you find signs of a failed water pump, a blown head gasket, or persistent overheating after basic checks, seek a mechanic promptly.

When to seek professional help

Rapid engine overheating can cause severe and costly damage. If you notice persistent overheating despite basic checks, coolant loss, white or sweet-smelling exhaust, white smoke from the exhaust, milky engine oil, or if the temperature continues to climb after stopping and cooling, arrange professional diagnostic and repair services as soon as possible. A qualified technician can perform pressure tests, leak detection, thermistor and thermostat testing, radiator flow checks, and more advanced diagnostics to pinpoint the exact cause.

What to ask your mechanic

Being prepared can save time and money. When you visit or call a shop, consider asking:

• What is the most likely cause of the overheating based on symptoms?


• What tests will be performed, and will they provide a written report and estimate?


• Are there any immediate driving restrictions or precautions I should follow?

Getting clear explanations and a detailed repair plan helps you understand the fixes and their necessity, and ensures you’re not paying for unnecessary parts or procedures.

Summary

High coolant temperature is a warning sign that the engine cooling system is not effectively removing heat. Start with immediate safety steps, inspect for leaks and obvious damage, and perform basic checks of coolant level, hoses, radiator cap, and fans. Understanding common causes—from a stuck thermostat to a failing water pump or air in the system—can guide your next action. If simple checks don’t restore normal temperature or if you notice persistent leaks or unusual symptoms, consult a qualified mechanic promptly to prevent engine damage.

How do I lower the coolant temperature?

To lower a vehicle's coolant temperature, use the heater on full blast, turn off the A/C, and, if possible, shift into neutral and gently rev the engine to circulate coolant faster. If the temperature continues to rise, pull over safely and turn off the engine to let it cool down before checking for problems like leaks or low coolant levels.
 
Temporary measures while driving

• Turn on the heater: Turn your car's heater to full blast and the fan to its highest setting. This transfers heat from the engine coolant to the cabin. 
• Turn off the A/C: The air conditioning puts an extra load on the engine, so turn it off to reduce strain. 
• Rev the engine: If you are stopped or in traffic, shift to neutral or park and gently rev the engine (around 1500 RPM) to increase the circulation of coolant and the speed of the fans. 

If the temperature keeps rising

• Pull over safely: Find a safe place to stop and turn off the engine as soon as possible. 
• Open the hood: Lift the hood to allow heat to dissipate from the engine compartment more quickly. 
• Wait for it to cool: Do not open the radiator cap while the engine is hot, as the system is under pressure and could cause burns. Wait for the engine to cool down completely before proceeding. 

Long-term solutions

• Check coolant levels: Regularly inspect the coolant reservoir and add the correct coolant or a 50/50 mix of coolant and distilled water if the level is low. 
• Inspect for leaks: Look for any signs of leaks around the hoses, radiator, or water pump. 
• Flush and replace coolant: Have the cooling system flushed and the old coolant replaced to remove blockages and built-up scale. 
• Service the radiator and fans: Make sure the radiator isn't blocked and that the cooling fans are working correctly. Consider having the system professionally serviced if problems persist. 

Can an overheating car be fixed?

Yes, an overheating car can often be fixed, but the solution depends on the cause, which can range from a simple fix like adding coolant to a more complex one like replacing a part like the water pump. Common fixes include checking for and repairing leaks, performing a coolant flush, replacing parts like the thermostat or water pump, or clearing blockages from the radiator. If the issue is not immediately apparent or a simple fix doesn't work, it's best to have the car professionally inspected.
 
This video explains what to do when your car is overheating: 57sTeam O'NeilYouTube · Oct 24, 2013
What to do immediately

• Turn on the heater and fan: This will help draw heat away from the engine. 
• Pull over and turn off the engine: Do not continue driving if the temperature gauge remains high. 
• Let the engine cool down completely: before attempting any checks. 

Potential fixes and part replacements

• Check and add coolant: Low coolant is a common cause of overheating. 
• Inspect for leaks: Look for leaks in hoses, the radiator, or the water pump. 
• Perform a cooling system flush: This can remove blockages and old fluid. 
• Replace faulty parts: This may include the thermostat, radiator, water pump, or fan relay. 
• Clear blockages: Clean the front of the radiator if it's blocked by debris like mud or leaves. 
• Replace a bad serpentine belt: A damaged belt can prevent the water pump from working correctly. 

When to seek professional help

• If the overheating continues after basic checks. 
• If you are not comfortable diagnosing or repairing the issue yourself. 
• If the engine was driven for an extended period while overheating, as this could cause serious internal damage that requires professional assessment. 

What does it mean when your coolant temperature is high?

Engine coolant over temperature means your engine is overheating, which requires immediate attention to prevent serious and costly damage. The warning light indicates the engine's temperature has exceeded its normal operating range due to issues like a coolant leak, a faulty thermostat or water pump, or a broken radiator fan. When the light comes on, safely pull over, turn off the engine, and let it cool down before inspecting or attempting any repairs.
 
What to do immediately

• Pull over safely: Find a safe place to stop your car as quickly as possible. 
• Turn off the engine: Shutting down the engine will prevent further overheating. 
• Turn off the A/C: The air conditioning system puts extra load on the engine, so turning it off can help it cool down faster. 
• Do not open the hood immediately: Wait for the engine to cool down significantly before opening the hood, and never open the radiator cap when the engine is hot, as pressurized boiling liquid can cause severe burns. 

Common causes

• Low coolant level: Caused by leaks in hoses, the radiator, or other components. 
• Faulty thermostat: The thermostat may be stuck closed, preventing coolant from circulating properly. 
• Malfunctioning water pump: A broken water pump will not circulate the coolant through the engine. 
• Broken radiator fan: If the fan doesn't work, the radiator can't cool the coolant effectively. 
• Damaged radiator: Leaks or blockages in the radiator can prevent it from dissipating heat. 

What to do after cooling down

• Check coolant level: Once the engine is cool, carefully check the coolant level in the reservoir. 
• Inspect for leaks: Look for any visible leaks in the radiator, hoses, or under the car. 
• Seek professional help: Even if you add coolant, the underlying issue needs to be diagnosed and fixed by a professional mechanic. Continuing to drive with an overheating engine can cause severe damage, such as a blown head gasket or a warped engine block. 

Can I drive with a high coolant temperature?

No, you cannot drive with an engine coolant over temperature warning because it means your engine is overheating, and continuing to drive can cause severe, irreversible engine damage, such as a warped cylinder head or seized pistons. You should immediately find a safe place to pull over, turn off the engine, and let it cool down before taking further action.
 
This video explains what happens to engine coolant temperature under different conditions: 56sHigh Performance AcademyYouTube · Aug 2, 2023
What to do immediately

• Turn off your air conditioning to reduce the load on the engine. 
• Turn on the heater to full blast. This draws heat away from the engine and into the car's cabin. 
• Find a safe place to pull over as quickly as possible. 
• Gently pull over and shut off the engine. 

What to do after stopping

• Do not open the hood immediately, as steam and hot components can cause severe burns. 
• Allow the engine to cool down for at least 15-30 minutes before attempting to open the hood or check anything. 
• Do not open the radiator cap until the engine is completely cool, as the pressurized, hot coolant can cause it to spray out and scald you. 
• Once cooled, check the coolant level in the overflow tank. If it's low, you may need to add coolant or water to get to a repair shop. However, it's best to have it towed to avoid further damage. 
• Call for roadside assistance to have your vehicle towed to a repair shop for a proper inspection and repair.