[ANSWERED] Why Does My Coolant Reservoir Keeps Emptying? How to Fix It?

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If your coolant reservoir keeps emptying, you have come to the right place. I have covered this issue in detail, explaining why it happens and how to fix it. Make sure you read the complete article to identify and solve the problem correctly. 


Signs Of Low Coolant In Car

Below are some of the most common ”low coolant level” signs:

  1. Symptom 1: Overheating Engine
  2. Symptom 2: Heater malfunctioning
  3. Symptom 3: Low or No Coolant Level
  4. Symptom 4: Steam from under the hood
  5. Symptom 5: Radiator hoses collapsing
  6. Symptom 6: Sweet smell from the engine
  7. Symptom 7: Pool of coolant under the car
  8. Symptom 8: The oil seems like chocolate milk and has a raised level on dipstick


Why does the coolant reservoir keeps emptying?

There is no one-line answer to this question; the reason can be a hole in the radiator, damaged water pump seal, blown head gasket, air lock in the coolant system, etc. In the next section, we have covered most of the reasons behind this problem and how to fix the reservoir emptying issues. 


How do we diagnose and fix the coolant reservoir keeps emptying issue?

Before we dive into the potential causes and the solution, make sure you do not drive your car, and I recommend not starting it as well. Engine without coolant heats up quickly and would result in permanent damage. 

1) Faulty radiator cap

The radiator cap has a pressure valve that maintains the pressure in the cooling system at around 15 PSI. As the coolant heats, the pressure starts increasing; if the pressure valve of the radiator cap is not working, the coolant will start overflowing out of the overflow pipe. You can attach a water bottle to the end of the overflow pipe to see if coolant is indeed overflowing through it. If it is, simply replacing the cap will solve the issue. 

2) Airlock in the coolant system 

“Airlock” is trapped air in the engine block, radiator, hoses, and heater coil; it usually occurs if you drain the coolant system to repair parts. Upon refilling the coolant, air pockets will prevent the coolant from getting inside the system, and it may appear like the coolant is refilled, but in reality, it’s not. 

To fix the airlock issue, you must remove the trapped air pockets from the cooling system by bleeding it. Bleeding the coolant system can be done at home; all you need is a fluid funnel, and you can follow the steps mentioned in the YouTube video attached below:


3) Coolant hose leak

Heat and abrasion are mostly the reasons behind the ruptured coolant hose; in some cases, the hose clamp can also be snapped, resulting in leaking coolant. 

Locate the coolant hose to check if it’s ruptured or if the clamp is snapped. If the clamp is snapped and the hose is intact, simply replace the clamp; if the hose is busted, you will have to replace it, too.

A coolant hose can cost $45 to $375, depending on the make and model of your car.

4) Cracked reservoir 

The reservoir can be cracked after bearing temperature fluctuations for years. The coolant can seep through these cracks, resulting in an empty reservoir. Inspect the tank for cracks and get it replaced if it’s damaged.

5) Blown head gasket

If the head gasket is blown, the coolant will enter the oiling system and the combustion chamber. Check the oil filler cap and the dipstick; if your oil looks like chocolate milk, that is a clear sign the head gasket is blown, and coolant is mixed with engine oil.

This will cause white smoke to come out of the exhaust pipe (which happens because the coolant evaporates) and other serious problems. A blown head gasket can burn a hole in your pocket, and if you keep driving the car in that condition, it will only get worse. Take the car to a mechanic and get it fixed.

6) Leaked radiator

The radiator can leak due to collision or corrosion, creating holes and cracks in the radiator over time. The coolant will start seeping out of radiator cracks and holes. To quickly identify a coolant leak, wash the radiator with water and then look for leaking coolant. 

Read: How to detect and repair a radiator or coolant leak.

Keep in mind sometimes the radiator can have small holes that may not be spotted easily; it can evaporate coolant without any noticeable leak. If that’s your situation, you should run a smoke test and get the holes patched by an expert. 

7) Failing water pump seal

The water pump seal keeps the water pump in place; since it is made of rubber, it can harden and eventually crack with time, resulting in a coolant leak. The water pump seal is pretty cheap, but the replacement process requires skills, so only attempt to fix it yourself if you have previous experience. 

8) The thermostat is not opening, causing the coolant not to circulate as it should

The thermostat is responsible for maintaining the flow of coolant between the engine and the radiator. As the temperature rises, the thermostat allows the coolant to flow, and when the engine temperature drops, the thermostat closes. If it is not working correctly, the coolant will not circulate as it should, causing it to boil and eventually resulting in overflow from the reservoir. 


Should you drive with the coolant reservoir being empty?

No, driving the car without coolant can cause serious problems, including complete engine failure. The coolant absorbs heat and keeps the engine cool; not having coolant and driving will cause overheating that will damage your car’s engine. This overheating will trigger dashboard warning lights, and eventually, the engine will be seized. 



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