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Does Coolant Level Drop When Engine Is Hot? (Explained)

The coolant system in your vehicle plays a crucial role in maintaining the temperature of your engine. The coolant, also known as antifreeze, is a mixture of water and glycol that circulates through the engine block, absorbing and dissipating heat.


One of the most common questions that car owners ask is whether the coolant level drops when the engine is hot.


In this article, we will explore if coolant level drops when the engine is hot, discuss how the coolant system works, and answer other related questions.


Table of Contents:


a car coolant reservoir tank

Does Coolant Level Drop When Engine Is Hot?

The short answer to this question is no, the coolant level can rise slightly when the engine is hot. This is due to a phenomenon known as thermal expansion. As the coolant fluid and water heats up, it expands, and some of the coolant can be pushed into the reservoir tank.


This is a normal and necessary process, as it prevents the coolant from boiling over and causing damage to the engine. However, if the coolant level rises too much, it can lead to overflow and loss of coolant which is why it's important to not overfill your coolant reservoir.


> Read how to remove an overfilled coolant reservoir here


Does Coolant Evaporate When Hot?

Another factor that can contribute to a drop or rise in coolant level is evaporation. The coolant in the system is exposed to high temperatures, which can cause some of the water in the cooling system to evaporate.


However, most coolant systems are pressurised and don't allow evaporated gases to escape the system.


Is It Normal for Coolant Level to Drop When Engine Is Hot?

No, coolant shouldn't drop when the engine is hot. It is normal for the coolant level to rise slightly when the engine is hot due to thermal expansion and evaporation.


If the coolant level lowers significantly, it can be an indication of a malfunction in the engine cooling system. This is why it is important to regularly check the coolant level, especially before taking a long trip or if you suspect an issue.


What Should My Coolant Level Be When Hot?

The ideal coolant level when the engine is hot is between the "min" and "max" marks on the reservoir tank.


The "max" mark indicates the level the coolant should be at the maximum and the "min" mark indicates the level when the engine is cold. The coolant level should be between these two marks, regardless of whether the engine is hot or cold.


Should Coolant Be at Max When Cold or Hot?

The coolant level should be at or above the "min" mark when the engine is cold. It is not necessary to have the coolant level at the "min" or "max" mark but it should be between the minimum and maximum lines.


Overfilling the coolant system can cause the coolant to overflow and be expelled through the pressure relief valve and coolant expansion tank, leading to a loss of coolant fluid.


Can I Use Water Instead of Coolant?

It is not recommended to use water instead of coolant in your vehicle. The coolant is specifically designed to withstand the high temperatures of the engine and protect against freezing and overheating.


Water, on the other hand, can boil at a lower temperature and can cause corrosion and rust in the engine. Additionally, the coolant provides important chemical properties that prevent corrosion, rust and other issues in the engine.


However, you can use water as a temporary fix for a low coolant level if you must drive.


Conclusion

In conclusion, the coolant level can rise when the engine is hot due to thermal expansion. If the coolant level lowers significantly or frequently, it is important to have it checked.


It is important to regularly check the coolant level, especially before taking a long trip or if you suspect a malfunction. It is also essential to use the correct type and mixture of coolant for your vehicle, as recommended by the manufacturer.

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