Coolant in the engine is essential for preventing overheating and maintaining the proper engine temperature. A reservoir linked to the radiator contains coolant. Radiators transfer heat from the coolant and cool it down.

If there is insufficient coolant in the engine, the engine may overheat. Excess coolant can also potentially overflow the coolant reservoir tank. Let’s look at how much coolant should be in the reservoir.

How Full Should the Coolant Reservoir Tank Be?

The engine coolant level in the reservoir must be correct. The reservoir should be at least 30% full in order to cool the engine effectively. The coolant reservoir is positioned on the upper right-hand side of the engine compartment. The reservoir is a translucent tank made of plastic with “L” and “F” markings on it.

  • If the coolant level is less than the “L” (low) indications, it is too low. In that scenario, you should add more coolant to prevent overheating. 
  • If the coolant level is higher than the “F” (full) level, the reservoir is overfilled. The coolant should be flushed in that situation.

How Much Coolant Do I Need to Fill an Empty Radiator

The size of the coolant reservoir determines this. Most automobiles will require approximately 5 liters of coolant. A small four-cylinder engine can contain about 6-7 quarts of coolant, whereas a V8 engine may handle more than 16 quarts.

For the coolant mixture to work effectively, 50% antifreeze is combined with 50% water in most engines. Smaller the engine, the lower the percentage of antifreeze required. Fill the reservoir with coolant until it reaches the “MAX” or “FULL” markings.

How Often Should You Top Up Coolant?

Unless there is a leak, coolant can last a very long time. Coolant can last for an expected duration of 30,000 miles or two years. The average coolant loss is 0.25 percent every four to six months, resulting in two to three ounces lost annually. The coolant level may drop more quickly if there’s a leak; in that case, you should top it up with more coolant.

Can You Put Water in the Coolant?

It is not advised to drive the car if the coolant level is below the “MIN” or “LOW” marking unless you add more antifreeze. To maintain a proper coolant system, water and antifreeze are added to radiators in a 50-50 ratio.

However, you can add water to your coolant reservoir if you need some coolant in an emergency or to get to the nearest repair shop. This can reduce the coolant’s antifreeze and anti corrosion properties. After visiting a repair shop, make sure to ask the mechanic to correct the water-to-antifreeze ratio.

Where Should the Coolant Level Be When Cold?

Coolant contracts during the winter. A vacuum is generated as the pressure in the radiator decreases. This vacuum sucks coolant into the radiator, lowering the coolant level.

If your coolant level is slightly higher than “low,”  it may appear below “low” in the cold. Coolant will expand as the engine heats up. So, if your coolant level is between “low” and “full” on the reservoir, it is normal.

Why is My Coolant Reservoir Empty After Filling?

Coolant is most likely leaking if the reservoir has been filled with coolant, but the level is still low. Let’s examine some of the causes of low coolant levels.

  • The function of the radiator cap is to direct coolant into the overflow tank. The radiator cap may become faulty, allowing too much coolant to be released.
  • Head gaskets are crucial to maintaining compression and sealing the combustion chamber. Due to a blown head gasket, coolant might leak into the cylinder.


The system may blockage if your radiator is full but your coolant reservoir is low. The main causes of a coolant system blockage include a blocked thermostat, a malfunctioning water pump, or sediment buildup in the radiator.

Always wait until the engine has cooled before examining the coolant level. The reservoir should contain at least 30% coolant and be less than the "full" or "max" mark. If the radiator is full and the coolant is hot, it will expand and overflow into the reservoir.

It is not suggested to fill the coolant beyond the "full" or "max" indications. Most cars lack a drain tube to handle overflowing coolant, which allows it to spill onto engine components. This may cause the engine to smell like burned coolant. If fluid overflows, it can potentially harm the engine's electrical wiring.


To summarize, coolant is required to prevent the engine from overheating. It is essential that the coolant level in the engine is not too high or too low. The level of coolant should always be between the “low” and “full” markings. If the coolant level is below the “MIN” point, you can top it up. If the coolant level drops quickly due to leaks, contact a mechanic immediately in that case.

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