Engine coolant over temperature warning: Causes & what to do

Engine coolant over temperature warning: Causes & what to do
Engine coolant over temperature warning signals that your car engine is overheating. There are two potential causes: aggressive driving styles, or technical faults. 
In the first case scenario, it’s enough to let off the throttle and allow the car to roll without putting much load on the engine. It’s better not to shut off the engine, as the additional air flow helps to cool down the engine. 
If the former method doesn't work, it may indicate a serious problem – find a suitable location to pull over and turn off the engine. 
Avoid opening the hood immediately, especially, don't open the coolant reservoir, as the hot vapor escaping from the cooling system may cause burns. 
It is unlikely you'll be able to make field repairs that will allow you to continue driving your vehicle freely. Once the engine has cooled off, you should drive to the nearest auto repair shop. If your engine continues to overheat quickly, call a tow truck instead. 
Pro tip: The first thing you should do when you notice a rise in coolant's temperature is to turn on the interior heating to full blast. The extra airflow through the cabin radiator will help the engine cool down more efficiently. 
Vehicle dashboard display showing a warning message "Engine Coolant Over Temperature" with a coolant warning icon.

What are the signs of an overheating engine? 

The red engine temperature warning light on a dashboard is the easiest way to spot an overheating engine. However, the engine temperature gauge can give you clues about rising temperatures even sooner. 
A normal engine temperature varies from 70°C to 105°C (160°F to 221°F). A wider range than that is indicated in your engine temperature gauge, even though it’s usually only separated into C (stands for “cold”) and H (stands for “hot”). Your engine temperature shouldn't reach H. 
The engine coolant temperature light should be your cue to pull over as soon as possible. Continuing to drive and raising the engine temperature even more may cause serious damage (such as blown gaskets or warped cylinder head) to your vehicle. 
Besides the engine coolant over temperature warning light and the dashboard gauge, there may also be other symptoms: 
  • Steam (which may look like smoke) coming out of the engine compartment. If your engine is overheating, that may cause the coolant to boil and escape as vapor through the radiator or overflow tank. 
  • Unusual smells. A boiling coolant may give a mixed sense of hot, sweet, and burning smells. 
  • Thumping noises. In some cases, the boiling coolant will create bubbles that will cause various noises in the cooling system. 
  • Reduced engine power. Sometimes, the vehicle may activate the limp mode to protect itself from more severe damage. 
All these signs, along with the engine temperature warning light, indicate that you need to address major issues as soon as possible. 
As we said, you should pull over as soon as possible to at least let the car engine dissipate the excess heat. Then, either get the car towed or drive carefully to the nearest auto repair shop. 
Close-up of a car's coolant temperature gauge indicating engine overheating, with the needle approaching the red 'H' zone.

Reasons why engines overheat 

When your car is running hot, it could be caused by many different things. But most of the time, they're not too complicated or expensive to fix – assuming you haven’t caused any additional damage to your vehicle’s engine. 
Low coolant level or a coolant leak 
If the cause of engine overheating is a low coolant level, that’s the best-case scenario. Simply topping off the coolant will resolve the issue. In the future, remember to check the coolant levels regularly, and such issues will be easily avoided. 
Coolant leaks, however, can be slightly more expensive as different components may cause them. While it’s unlikely that you’ll have to replace the entire cooling system, parts such as the radiator can be quite costly. 
An engine coolant reservoir with visible 'MAX' and 'MIN' level markings, containing coolant fluid below 'MIN' level.
Faulty thermostat 
A faulty thermostat might not let enough coolant flow. This may disrupt the engine's ability to regulate temperature. 
Malfunctioning thermostats can cause two types of issues. If it is stuck closed, the temperature rises quickly and falls slowly. If it gets stuck in an open state, the engine will have trouble maintaining proper operating temperature.  
Replacing a thermostat is not a big deal as long as you address the issue quickly. They’re relatively affordable compared to other parts. 
Radiator issues 
Radiators can cause issues in several ways – most often through a malfunctioning radiator fan or clogged pipes. Both of these cause problems in dissipating heat, either by restricting coolant or air flow. 
In cases of a dirty or clogged radiator, flushing and cleaning out the radiator pipes may resolve the issue and is a cheap fix. Replacing the fan or the entire radiator is more difficult and expensive. 
Finally, a faulty radiator cap may be the culprit as well. It’s intended to maintain proper pressure in the cooling system and engine block. 
If the radiator cap is malfunctioning, pressure levels could drop to the point where the coolant boils at lower temperatures than intended. Luckily, they are relatively easy and inexpensive to replace. 
Faulty water pump 
A water pump manages the circulating coolant to absorb the heat from the car’s engine. As with many of the other causes, a malfunctioning water pump may restrict the proper flow of coolant. 
Regularly inspecting and maintaining your water pump can help you avoid expensive replacements down the line. 
A person's hand holding a corroded car water pump next to a new one, highlighting the comparison between the two components.
Trapped air in cooling system 
Air bubbles in the cooling system can cause inefficient engine cooling. This can occur due to incomplete radiator fill-up or blocked coolant passages. 
Depending on the malfunctioning part, there may be many potential fixes to the problem. A radiator bleed, however, is a simple fix that could resolve the issue entirely. 
High ambient temperature 
While high ambient temperature typically doesn't increase engine temperature alone, it can make other cooling system issues worse. 
Leaking head gasket 
The head gasket prevents engine oil and coolant from mixing. A damaged one may fail to prevent such mixture or introduce gas from the cylinder into the cooling system. If the pressure in the cooling system drops, it can lower the coolant boiling point. 
A common cause of head gasket leaks is a warped cylinder head due to the engine's previous exposure to high temperatures. 
Early detection of cooling system issues and the prevention of overheating can save you money. Most problems can be solved for a fraction of the cost. However, repairing a damaged head gasket and cylinder head due to overheating can be extremely expensive, with labor alone costing several thousands. 
Get wireless diagnostic tool