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. Vehicles can either be liquid-cooled or air-cooled. Though, it is uncommon to see a vehicle manufactured with an air-cooling system.

Note that this article is focused 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 a few other components.

So, we will concentrate on the signs of no coolant in the radiator but the 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.

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 is heated and 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 airflow toward the engine compartment from the car’s grill. Immediately the liquid is cooled, it flows back to the engine to reduce its temperature.

coolant reservoir full but radiator empty

Signs of No Coolant in the Radiator, but the Reservoir is Full.

The common reason for no coolant in radiator but the reservoir is full is a blown head gasket. If a head gasket blows, the combustion gases from the cylinders will leak into the cooling system and push the coolant into the reservoir. Once the reservoir gets filled, the rest will waste through the overflow outlet.

However, other factors can cause issues in the cooling system. It could be as a result of lousy thermostat, bad radiator, and other related cooling system parts. Let’s look at these possible causes.

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 common sign that shows no coolant in the radiator is coolant leaks from the car. It can be dropping from the radiator or the hoses. The radiator’s coolant level becomes low if it has been punctured. This will cause the engine to overheat because no coolant absorbs its temperature.

Discoloration of coolant

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

Engine check light

If the radiator has no coolant, there will be a high increase in the engine’s temperature. This will turn the engine check light on so that the driver will know that there is an issue. You must track and fix the root cause to prevent a major engine damage.

Persistent odor

You might constantly perceive a sweet smell when you are around or inside your car. The coolant’s smell 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’s best to 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 may mean that the radiator’s coolant level is very low and should be refilled. However, if you see the release of white smoke from the exhaust, the damage is already done.

So, don’t wait until you see this sign before taking necessary actions

A damaged radiator cap

The radiator cap is responsible for making sure the coolant do not escape and keeping it at the right pressure. If you have a damaged radiator cap, it will cause coolant leak, leading to a low coolant level.

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

Torn radiator hose

The radiator hoses are always transporting hot fluid. As a result, the hoses will eventually wear out and tear. Especially if your vehicle is used for daily long trips, the hoses will likely wear out fast. The hoses might even explode, causing coolant to flow out from it easily.

Faulty head gasket

A damaged head gasket will turn the engine check light on. The head gasket is responsible for sealing the space between the cylinder and the engine block. It also facilitates the smooth flow of oil and coolant. If the head gasket blows, it will allow coolant to enter and burn in the combustion chambers.

Damaged intake manifold gasket

This component is located on top of the engine. The intake manifold provides fuel and airstream to the combustion chamber. A gasket is found inside the intake manifold, where it merges with the engine. This gasket 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, preventing engine overheat. The water pump circulates coolant to other engine parts. It is responsible for the easy flow of coolant through the radiator and engine block. If the component becomes faulty, it’ll cause a severe leak.

coolant reservoir does not return to radiator

How do you fix this issue?

I will highlight some ways to resolve the issue of no coolant in the radiator but the reservoir is full. These tips will aid you to protect your vehicle and also enable you to handle the situations above.

If your radiator cap is damaged, you will need to replace it with a good one. You need the right tools for this task. However, you have to make sure that the engine is cool and you purchased the right cap. Contact a mechanic if you are not a DIYer.

If a torn radiator hose is the cause, you have to park your car and let it cool down. After that, check if there is any leakage of coolant under your vehicle.

Examine if there is any liquid on the surface of the hoses. Tighten the hose clamp if you notice any leakage, and see if it resolves the problem. If it works, you do not need to replace the entire radiator hoses.

If the radiator or water pump is bad, the best solution is to replace it.

A head gasket blown is a major issue, and it is quite expensive to fix. If you have a blown head gasket, you need to decide if the head cylinder is worth the repair due to high repair cost. Fixing this issue will involve changing some expensive components.

Contact your mechanic to fix this issue because it is a critical job.

After fixing it, refill the 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, contact a mechanic.  The mechanic should diagnose the vehicle and proffer a solution.

Frequently Asked Questions (FAQs)

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

The common reason the coolant reservoir is full but the radiator is empty is an indication of a coolant leak from the car. It could be a result of bad thermostat housing, bad radiator, or other related parts. Other possible causes are coolant leaks, blown head gaskets, and bad water pumps.

Why is coolant not returning from the overflow tank?

The common reason coolant is not returning to the overflow tank is a coolant leakage. It could be from the radiator hoses, cap, water pump, or the radiator itself. If the radiator cap is faulty, it will allow engine coolant to escape, and this will lead to the coolant not returning to the reservoir.

Does the radiator reservoir need to be full?

The radiator reservoir is an important component in the engine cooling system. It needs to reach the maximum line.

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.

Why is the coolant reservoir empty?

If the coolant reservoir is empty, you have a leak in the system. A damaged reservoir tank can cause evaporation of the coolant, which 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.

Do you put coolant in the radiator or reservoir?

It is recommended to pour coolant directly into the reservoir when topping off the reservoir. But if you are changing the coolant, then you should pour the engine coolant through the radiator.

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.  This will help you to timely handle issues like no coolant in the radiator but the reservoir tank is full and also to prevent damage to the engine.

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Osuagwu Solomon

Osuagwu Solomon is a certified mechanic with over a decade of experience in the mechanic garage, and he has over five years of experience in the writing industry. He started writing automotive articles to share his garage experience with car enthusiasts and armature mechanics. If he is not in the garage fixing challenging mechanical problems, he is writing automotive repair guides, buyer’s guides, and car and tools comparisons.

One thought on “Why No Coolant In Radiator But Reservoir Tank Is Full?

  1. Thru all that you never explained why th coolant from th reservoir doesn’t go into radiator if none in radiator

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