Why No Coolant In Radiator But Reservoir Tank Is Full?

The engine cooling system plays a very important role in the efficient operation of the engine of all motorcycles, trucks, or automobiles. Vehicles can either be liquid-cooled or air-cooled, but it is uncommon to see a vehicle manufactured with an air-cooling system. Consequently, we will concentrate on the signs of no coolant in radiator but reservoir tank is full, the causes of lack of coolant in the radiator when there is a full reservoir tank, and the ways to fix this issue.

Note that this article is focused solely on liquid cooling systems. The liquid cooling system of a vehicle consists of various components. It includes; the radiator, which is mostly an aluminum radiator, the thermostat, hoses, water pump or coolant pump, a radiator cooling fan, heater core, bypass system, head gaskets, and few other components.

The liquid cooling systems function by transporting the coolant through a passage in the engine blocks and heads. The coolant picks up heat as it passes through the engine. The coolant heated then flows to the radiator through a rubber hose. The heated coolant moves through the thin tubes in the radiator, and it is cooled by the flow of air towards the engine compartment from the car’s grill. Immediately the liquid is cooled. It flows back to the engine to reduce its temperature.

Signs of no coolant in the radiator, but the reservoir is full.

These are some of the common signs you are going to experience when there is no coolant in the radiator of your vehicle irrespective of the fact that your reservoir tank might be full:

The engine will begin to overheat.

It is a very common sign that reflects that something is wrong with the cooling system. It can be due to a faulty radiator or a bad thermostat or even other related issues. This problem can drastically reduce the functionality of the vehicle due to engine poor performance. Overheating the engine will produce smoke, and It might lead to a sudden breakdown of the vehicle.

The heater may be malfunctioning.

When the heater in the car does not function, it is a sign that there might not be coolant in the radiator. The heater depends on the hot fluid that flows through the core. As the hot fluid flows, it releases hot air that blows into the car.

Leakage of coolant.

Another sign that shows no coolant in the radiator is when you start noticing the coolant is leaking from under your car. It can be dropping from either the radiator or the hoses. The radiator’s coolant level becomes low if it has been punctured or completely damaged, and this causes the engine to overheat because there is no coolant to absorb its temperature.

Discoloration of coolant.

The lack or shortage of coolant in the radiator can cause the coolant to change in color. The coolant of vehicles is mostly green, yellow, or pink. This color can change to a thick brown-like color if there is a contamination. This can obstruct the flow, and it can also clog the radiator.

The engine check light will be illuminated.

If the radiator has no coolant, there will be a high increase in the engine’s temperature, and this will turn the engine check light on so that the driver will know that there is an issue, and it needs to be fixed to prevent complete damage of the vehicle.

Persistent odor.

You might constantly perceive a sweet smell when you are around or inside your car. The odor of coolants is noted as a sweet smell. Therefore, perceiving this type of smell can signify that there might be a leakage of coolant under your car. It would be best if you still investigate further to be sure of the cause.

Smoke from the engine.

If there is a release of white smoke from the exhaust of your vehicle. It signifies that the radiator’s coolant level is very low and should be refilled.
What causes no coolant in radiator but reservoir tank is full?

A damaged radiator cap

The radiator cap’s function is very important, and it plays a vital role in the functioning of your vehicle’s cooling system by making sure that the coolant is not allowed to escape and this component keeps the coolant inside the radiator at the right pressure. If you have a damaged radiator cap, the coolant will begin to leak, causing a shortage in the radiator’s coolant level.

A damaged radiator cap can also break the hoses by building high pressure in it, creating another channel for the escape of coolant. A faulty radiator cap can cause the coolant reservoir overflowing and overheating of the vehicle’s engine system.

Torn radiator hose

If the radiator hoses are always transporting hot fluid, then the hoses will wear out with and will finally tear. Especially if your vehicle is used for daily long trips, the hoses on your car will wear out fast. The hoses might even explode, causing coolant to flow out from it easily. A bad radiator can be responsible for coolant not flowing from reservoir to radiator due to leakages.

Faulty head gasket

A damaged head gasket will turn the engine check light on. The head gasket of your car is responsible for making a seal between the cylinder and the engine block. It also facilitates the smooth flow of oil and coolant. A head gasket blown can burn the fluid in the combustion chambers, which is very dangerous to your vehicle. You might not notice any leakage of coolant under your vehicle if the head gasket is faulty.

Damaged intake manifold gasket

This component is located at the side or on top of the engine. The intake manifold gasket provides fuel and airstream to the burnt cylinders in order to provide power. A gasket is found inside the intake manifold where it merges with the engine. This gasket at the connection area with the engine can get damaged, leading to leakage of coolant in your vehicle.

Bad radiator or water pump

The radiator helps to cool the heated coolant as it passes through its metal tubes; this prevents overheating of the engine. The water pump helps the system function at a moderate temperature; this pump is responsible for the easy flow of coolant through the radiator and engine block’s hoses. Damage to these components can cause a severe leakage in the cooling system.

How do you fix this issue?

I will highlight some ways to resolve the issue of no coolant in radiator but reservoir is full. These tips will aid you to protect your vehicle and also enable you to properly handle the situation where you are faced with any of the causes listed above:

coolant reservoir does not return to radiator

In a case where your radiator cap is damaged, you will need to replace the damaged radiator cap with a good one. If you know how to perform this task, you can carry it out with the right tools box, but you have to make sure that the engine is cool and the right radiator cap is purchased for your vehicle. If you do not know how to do this, you should hire the services of a mechanic to assist you with resolving this.

Going about this wrongly can increase the damage done to your vehicle. Radiator caps are not too expensive though it depends on the type you need.

Suppose you have a case of worn out or torn radiator hoses. You have to park your car on a dry surface and let it cool down. If possible, let the vehicle rest for several hours. Then you can investigate if there is any leakage of coolant under your vehicle. Examine if there is any liquid on the surface of the hoses. You can tighten the hose clamp if you notice any leakage, and if it works, you do not really need to replace the entire radiator hoses.

In a situation where you find out that the radiator or water pump is bad in your vehicle, you need to get your vehicle to a mechanic shop immediately. This kind of problem needs the attention of a well-trained mechanic because the coolant will have to be drained. Either the radiator or the water pump has to be changed. After this, the mechanic will have to fix the issue if no coolant in the radiator by refilling it.

A head gasket blown is a major issue, and it is quite expensive to fix. It is very risky if this should happen in your vehicle. If you are faced with this issue, you need to decide if the car head cylinder is worth the repair due to the high cost of repair. To fix this issue will involve changing some expensive components by a mechanic.

If only the intake manifold gasket is faulty, the mechanic can change only this component to resolve the issue; this is a far less issue compared to a blown head gasket.

If you notice that there is no coolant in the radiator, you might want to try refilling the radiator with coolant. Coolant levels in the radiator can decrease over time but after refilling, monitor it for some time. If you still notice a significant drop in the coolant level of the radiator without normal coolant loss, please take your vehicle to a mechanic shop for a proper check as this problem can be a result of several other issues.

Coolant Reservoir doesn’t drain back into Radiator – YouTube

Frequently Asked Questions (FAQs)

Q: What does it mean if your coolant reservoir is full, but the radiator is empty?

Suppose you notice that your radiator is empty, but your coolant reservoir tank is full. In that case, it might mean that there is or there are few damages in the components of the engine cooling system, which means that there is possibly a faulty radiator or radiator hose, a damaged gasket, or a radiator cap, or some other faulty components.

The moment you find out this problem, it is advisable that you first tighten the hose clamp and fillup the radiator with coolant because it is quite normal for the coolant level of the radiator to decrease with time. After doing this and you still notice a drastic fall in the coolant level. Then it is certain that there is a damaged component. You will have to get your car to the mechanic shop.

Q: Why is coolant not returning from the overflow tank?

When the overflowing coolant reservoir does not return to the radiator the hot coolant that needs to be cooled down, it means that there might be a leakage or clog of the radiator hoses that allow the flow of fluid from the coolant reservoir to the radiator. It can be a result of a damaged radiator cap. If your radiator cap is faulty, it will allow the escape of the coolant in the radiator, and this will lead to coolant not returning to the reservoir.

Q: Does the radiator reservoir need to be full?

The radiator reservoir is an important component in the engine cooling system. The radiator reservoir needs to reach the maximum line because it is where the new coolant is poured into the cooling system. The radiator reservoir stores the excess coolant until it is needed to reduce the temperature of the engine. If the coolant in the radiator reservoir is low, it can cause the engine to overheat. So you need to check the coolant level in the reservoir frequently.

Q: Why is the coolant reservoir empty?

Suppose the coolant reservoir tank is damaged or there is a leak due to overheating. In that case, it will cause the coolant reservoir to drip coolant, which can eventually empty the radiator slowly. A damaged reservoir tank can cause evaporation of the coolant; it is the cause of the coolant reservoir not filling up. The drop rate in the level of coolant depends on the extent of the damage.

The coolant level also decreases with time as you use the engine of your car, so you can try refilling the reservoir and observe for faults.

Q: Do you put coolant in the radiator or reservoir?

If your vehicle has a reservoir, the coolant should be added directly to the reservoir instead of the radiator. Except in a case where you have an empty reservoir tank, then you can add the coolant directly to the radiator but consequently top the radiator through the coolant reservoir.

Final Words

The cooling system of the vehicle does not just keep the engine at a moderate temperature. It ensures the smooth operation and high efficiency of the engine. This is one of the major reasons why you must frequently check the coolant level in your vehicle so that you will be able to timely handle issues like no coolant in radiator but reservoir tank is full and also to prevent damage to the entire engine due to a slight problem in the cooling system.

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Tito

Hi There, I am R. Hasan Tito, a mechanic, and owner of this website. My friend and I created this website to share our knowledge, expertise, and experience with our fellow mechanics' community and car users. I am a specialist and certified automotive mechanics (Both Heavy Commercial and Private Cars). I have been working as a mechanic for over fifteen years. I worked for a long time at Global Rebound Automotive companies (Toyota, TATA, BMW, Nissan, TVs, and Others ) as a Mechanic and Mechanics Supervisor.

3 thoughts on “Why No Coolant In Radiator But Reservoir Tank Is Full?

  1. Thank you for sharing your knowledge in vehicle, very well appreciated, we look forward for more interesting and helpful topic for a safe vehicle driving.. more power to you..

  2. Maybe the coolant in the reservoir is way beyond the max level. Coolant need some air to push it down into the radiator.

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