No Coolant in Radiator But Reservoir Tank is Full (WHY)

No Coolant in Radiator But Reservoir Tank is Full

The radiator and reservoir tank functions in the engine by ensuring the flow and availability of coolant in the engine. They are like two pieces of the same part working together to serve the same purpose of cooling the engine.

However, it is possible that there is fluid in the reservoir while the radiator is empty. This could be a cause for alarm for some people and nothing to worry about for others.

The reason for no coolant in the radiator buy reservoir tank is full could be coolant leakage, faulty head gasket, torn radiator hose, etc., and the remedy is to refill the radiator tank with more coolant or visit a professional for repairs and replacement if need be.

For someone that is observant, you will be able to tell when there is a problem in the engine because there are always signs such as discoloration of coolant, illumination of the check engine light, smoke from the engine, etc. The earlier you are able to pick up this sign the better for you and the car.

What Does it Mean for Coolant Reservoir to be Full but Radiator Tank is Empty?

The coolant reservoir and radiator are part of an engine’s cooling system that helps it function optimally. The coolant moves from the reservoir pass through some other component of the system while picking up heat as it goes to the radiator in order to get cooled by air before flowing back to the engine.

However, if your coolant reservoir is full but the radiator is empty, it means that the coolant isn’t getting inside the radiator tank, which is a pointer to a problem in the cooling system.

Some of the problems could be a damaged gasket, faulty radiator, bad radiator/coolant cap, and many more.

It is quite easy to detect if your radiator tank is empty, we will take a look at some common signs you are likely to experience.

  • Coolant Leakage: One sign you are sure to notice is leakage underneath the car. If any part of the radiator is damaged, coolant is sure to leak out because there’s nothing stopping it from flowing out. Leakage if not noticed in time will eventually leave the radiator tank empty.
  • Engine Check Light will be On: Whenever there is a rise in the temperature of the engine, the check light will come on indicating there is a problem that needs checking out.
  • Smoke Coming From the Engine: When the radiator tank is empty, it is very possible for the engine to release smoke usually white. This is an indicator that the tank needs to be refilled or checked for any problem.
  • Change in Coolant Color: Coolants are supposed to maintain a yellow, green, or pink color, but this color can change to brown due to contamination. Contaminated coolant can block the flow of coolant to the radiator.
  • Overheating: The engine tends to overheat if there is no coolant in the radiator because it exacts itself and its performance also reduces. Overheating in the car is usually a sign that enough or no cooling is happening in the engine.

All these and more are some ways to know if your radiator tank is empty.

Why No Coolant in Radiator But Reservoir Tank is Full?

When there is no coolant in the radiator it can be attributed to some issues in the cooling system. Some of the issues will be considered below;

1. Bad Radiator Cap

The radiator cap is very important as it ensures that the coolant remains in the tank when it is properly screwed in place. It is possible that over time the cap gets worn out or broken thereby allowing coolant to escape.

2. Damaged Radiator and Pump

The radiator is responsible for cooling the heated coolant when it passes through it while the water pump helps by keeping the system at a moderate temperature and damage to it can result in leakage.

3. Blown Gasket Head

A gasket head is a seal between the cylinder and engine block, and it is responsible for the free flow of coolant. Once the head gasket is damaged, coolant escapes and gets burnt in the combustion chambers. There will be no leakage if the gasket head is bad because the liquid gets burnt before it can flow out.

4. Worn Out Radiator Hose

The radiator hose is responsible for the passage of heated coolant and gets worn out over time. The radiator hose gets worn out faster especially if the car is usually taken on long trips. A worn-out hose will cause coolant to leak thereby stopping its flow to the radiator.

What To If No Coolant Is In Radiator But Reservoir Tank is Full

When you notice that there is no coolant in your radiator but the reservoir is full, you should refill it as it may not be anything serious. When refilling, it should be done directly in the radiator and not through the overflow tank.

If over time the coolant level keeps dropping, you may have to find out what the problem is by checking the radiator cap, head gasket, signs of leakage, etc.

You should find out what is causing the radiator tank not to retain fluid and have it fixed. It will be better to see a professional if you can’t seem to find out the problem by yourself.

Should I Add Coolant to the Radiator or Reservoir?

Coolant can be added to the radiator or reservoir but under certain conditions. It is usually better to add coolant directly to the radiator than in the reservoir, this is better if you are topping up and the car isn’t hot.

When adding coolant to the radiator, you should add a mix of water and coolant (50-50).

However, coolant can be added to the reservoir when the temperature begins to rise due to a shortage of coolant.

When the radiator is full, you can top up by adding coolant to the reservoir. It is not advisable to add coolant to the radiator when the reservoir is low.

Unless you want to mix the coolant with water, you may not add coolant directly inside the radiator if it has water inside already.


It is important to note that not all vehicles have a radiator cap, in this case, you do not have the option of adding coolant directly to the radiator. If the car has both radiator cap and reservoir, you should add to the radiator rather than the reservoir, especially for modern cars.