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Why Your Engine Coolant Is Not Filling Up: Simple Fixes

Open hood of a car with engine

Why Your Engine Coolant Is Not Filling Up: Simple Fixes

We can imagine exactly how it feels to have an amazing car, with a poor radiator engine always crossing the safe maximum temperature range. Richard McCuistian, an ASE Certified Master Automobile Technician, gives expert advice stating that anything that takes the engine temperature above the safe temperature range of 195-220 degrees Fahrenheit, will lead to overheating, damaging the radiator, coolant reservoir, and engine. 

As a concerned car owner, you can easily navigate this problem by tracing the causes to a leakage in the coolant reservoir, hoses, radiator, or water pump. These causes are proven to be true because, in a well-functioning cooling system, there should be a continuous loop of the coolant from your engine to the radiator into the reservoir, and back. When this is not happening, it indicates an abnormality. 

This engine abnormality is even more frustrating when you have tried easy fixes like adding a coolant, but it still doesn’t make any difference. Now, let’s explore these problems and show you the fixes that work.

What Does It Mean For the Engine Coolant Not To Fill Up?

man filling up with engine coolant
Photo by Envato Elements

Whenever you hear the complaint that engine coolant is not filling up, it implies that the radiator is not retaining coolant poured in directly to it or from the coolant reservoir. 

Alternatively,  it could mean that the coolant tends to disappear after each refill attempt. This is usually a big problem for the cooling system and needs to be resolved. But what are the causes?

Coolant Leakage:

Coolant leakage is the most common cause of engine coolant not filling up. A few times, this leakage is significant and can be seen in the form of dampness around the outer part of your radiator, your radiator hose, or your garage floor. 

Sometimes, it vaporizes through your defroster, and you rarely notice that. Leaking engine coolant can be caused by any of the following;

  1.  Small hole in your radiator – Usually caused by corrosion within the radiator.
  2. A cracked coolant hose – Usually caused by electrochemical degradation and constant high temperature.
  3. A water pump issue – Often caused by a wrong coolant mixture or the use of the wrong sealant paste. 

Your coolant can also leak through the damaged area if the heater core is damaged. This can lead to the overheating of the engine, as there is no coolant absorbing its rising temperature.

FIX: Checking for such leaks and engaging your mechanic for immediate repair of the leaking sites is very important, as a significant continuous leakage can cause further problems to the cooling system. You can check for coolant leaks by performing a coolant pressure test which allows you to gauge the pressure in your cooling system.

Damaged Head Gasket

blown head gasket
Photo by Envato Elements

The head gasket fits between the cylinders or cylinder block and the cylinder head of an internal combustion engine. It seals the engine’s combustion part to allow the engine’s coolant and oil to circulate properly. Plus, it ensures the engine chambers are well separated so that oil and coolant do not mix. Such a mixture causes a coagulation of the oil and makes it unable to properly lubricate the engine, which can equally lead to overheating of the engine.

A high-temperature engine causes a blown head gasket. When this happens, it makes your coolant burn and evaporates away. Often, a white smoky exhaust indicates a burning coolant, and a leaking gasket head causes this. 

At some other points, the leakage may be invisible, but the constant overheating makes it evident that your engine coolant is not filling up.

FIX: Getting your mechanic to fix a damaged gasket early is your best bet, as it can affect the engine of the vehicle when not promptly attended to. Aside from its effect on the engine block, it will cause you to spend a lot on engine coolants without solving the cooling problem of the engine.

Faulty Radiator Cap

faulty radiator cap
Photo by Envato Elements

It is easy to trivialize the radiator caps’ relevance in a vehicle. Still, the radiator cap plays a very vital role in the cooling system of your car. Essentially, it ensures that the coolant is retained in the radiator at the correct pressure. 

In addition, it pressurizes the cooling system and helps to redirect coolants into the radiator via the vacuum valve. A faulty radiator cap usually leads to an overflowing radiator, the air in the cooling system, and a collapse of the radiator hose, which invariably results in the loss of engine coolant. It can also cause an overflow into the coolant reservoir, causing overheating and engine damage.

FIX: Once you discover you have a faulty radiator cap, don’t hesitate to change it. It usually goes for between $10 – $20, which is much less the cost of fixing a damaged engine. Asides from changing the radiator cap, engage the service of an experienced mechanic to confirm if there have been secondary damages and ensure it is quickly fixed.

Final Words

car air conditioning
Photo by Envato Elements

The problem of engine coolant not filling up can be quickly discovered by a driver who pays attention to his temperature gauge while driving. Having routine radiator and reservoir checks in the mornings before driving out will also help you detect leakages in your garage. Taking precautions will cost you little and save you the cost of changing the entire cooling system of the vehicle or buying a new car engine due to damage by overheating.


Where do I put the coolant, in the radiator or reservoir?

If your vehicle has a coolant reservoir, that is the best place to fill the engine coolant when running short of coolant. However, when your reservoir is empty, you will need to fill it and add coolant directly into the radiator. Subsequently, you can fill it through it.

What engine coolant is the best for my car?

There are different engine coolants; hence, the best coolant for your car depends on the vehicle’s age, type, and place of manufacturer. Reading your car manual will help you identify the factory-recommended kind of engine coolant to use for your car. You can access such information online if you don’t have a car manual.

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