How to Find and Fix Leakage on the Coolant System

Cooling System

By Rodney (Mechanics)

Leakage on the coolant system is one of the most common problems with this component. Normally, the leakage on the coolant system is easy to find since you can notice the liquid seeping or dripping from the component that has leaks on them. You might also be able to notice the overheating condition of your engine. Meanwhile, your vehicle might also be equipped with an indicator lamp that shows a low coolant level.

You can usually inspect the level of your coolant visually by opening the hood and inspecting the cooling system. You might be able to notice the liquid on the engine, hoses, or radiator if the cooling liquid is actually leaking. There are different colors from the coolant depending on the type of antifreeze you use for the system, including green, yellow, or orange. Some antifreeze products also use ethylene glycol that will produce a sweet-smelling characteristic that you will notice if there is actually a leakage.

Some common places that might contribute to the leakage of your coolant include:

Water Pump. An improper sealing condition on the shaft will push the coolant out from the vent hole located under the water pump pulley shaft. If your engine uses a two-piece water pump that has a backing plate, the leakage might be located somewhere between the housing and the back cover. Another possible location for the leakage is on the gasket that seals the water pump located on the engine front cover. This condition can be inspected by looking for stains or discoloration around the outer part of your water pump.

Leaking Water Pump

Radiator. Leakage can also occur around the radiators especially on the upper or lower connections for the radiator hose. This condition usually occurred as a result of vibration. The most common location for the leakage on the radiator is around the cooling tubes located on the core headers. If you have a coolant that has not been replaced for a long time, corrosion might also happen that can cause leakage from the system. Newer vehicles are designed to operate around 8 to 14 PSI for the cooling system. But, your engine will leak coolant and experience overheating if the radiator cannot work properly to hold the pressure.

Badly Corroded Radiator

Hoses. Coolant leaks can also happen if there are cracks, pinholes, or damages on the radiator hose. This condition will usually result in hot coolant spraying out from the component. If the hose connection has been corroded, it might also allow leakage of coolant from the component. Some cases of leakage might only occur when the hoses got too hot.

Checking Hoses

Freeze Plugs. Your vehicle is normally equipped with casting plugs located on the sides of the engine block or the cylinder head. This component can experience corrosion from the inside which will lead to leakage of your coolant. This condition is hard to notice because the locations of the plugs are behind the exhaust manifold and other engine components. If your vehicle uses a V6 or V8 engine block, you can inspect the condition of the plugs from underneath the vehicle.

Heater Core. Your engine’s heater core is normally located under the dash inside the air conditioning unit. You will not be able to see leakage directly because the component is hard to see. But you can notice the leakage if the coolant has seeped out from the AC unit and dripped to the vehicle floor on the passenger side. You might be able to look for wet spots under the AC unit on the passenger side floor. One alternative to fix this problem is to replace the original heater core with an aftermarket one that is designed with copper or brass material.

Flush A Heater Core

Intake Manifold Gasket. The coolant leakage may also occur when the gasket for the intake manifold fails to seal the cylinder heads. This will allow coolant to enter the crankcase and drop to the outer part of your engine. Some vehicles are also equipped with intake manifold gaskets that are made from plastic and are notoriously known to fail at around 50,000 to 80,000 miles of travel.

Replace Intake Manifold Gasket

Internal Coolant Leaks

Internal coolant leakage is one of the worst problems to have on your vehicle. Not only that they are almost impossible to notice since the location is behind other components, but this condition will also require expensive repair costs to get fixed.

Bad Head Gasket – A bad head gasket is usually the most common reason for internal coolant leakage. The damage condition on the head gasket will allow the coolant to enter the cylinder and straight into the crankcase. If the coolant has leaked into the crankcase, the liquid will be able to dilute the oil and damage the engine bearings. Other than that, the leakage will be able to cause a fouling condition on your spark plugs, which will result in a lot of white smoke produced from the exhaust. Using a sealer product might be able to temporarily fix this problem if the leakage is not too bad. But in most cases, you will be required to replace the head gasket completely.

Bad Head Gasket

You may try to test the pressure of the cooling system if you suspect the problem occurs from the leaks on the head gasket. An internal leak on your engine can be noticed if the component has difficulty holding pressure. Another method is to use a “block tester” to diagnose leakage on the head gasket. This tool will draw air from the cooling system and direct it into a chamber that has been filled with a special blue-colored liquid. The gases from the engine combustion will react with the special liquid. You will be able to determine the leakage on the head gasket if the liquid changes color from blue to green.

The constant overheating from your engine is usually the most common reason for the failures of the head gasket. This is because when the overheating condition occurs, the components inside the engine will experience thermal expansion that can damage the head gasket. The damaged areas will start to crack and leakage will occur that will also let coolant and pressure escape from the engine.

Cracked Head or Block – A crack in the cooling jacket of the cylinder head or the engine block can also result in internal coolant leaks. This condition will allow coolant to leak into the cylinder from the crack on the combustion chamber. The coolant will then dilute the oil and will cause corrosion on the piston and the rings. Fouling on the oxygen sensor can also occur if the coolant that you use contains silicates. The vehicle might also experience difficulty starting if there is a large amount of coolant sitting overnight in the cylinder. This condition can be checked using a block checker to diagnose the pressure point.

If the coolant has leaked into the crankcase, your problem might be from the damage conditions of the bearings. You can notice this condition by checking the oil level from the dipstick, which will appear a lot higher than the normal level. Besides, the contamination of the coolant will result in the discoloration of the oil.

Cracked Cylinder Head

Leaky ATF oil cooler – Internal coolant leakage can also happen on the component of the transmission fluid oil cooler. The ATF is normally routed using an oil cooler on automatic vehicles. The leakage of coolant will be able to damage the transmission line and contaminate the fluid. This will damage the transmission component. One symptom of this condition is drops of oil that look red or brown under the component. You can usually fix this problem by replacing the radiator and changing the transmission fluid.

Leaky ATF Oil Cooler

Performing Pressure Testing to Check Leakage on the Cooling System

You might need to check whether the cooling system is able to hold the pressure. One method to do this is to top up the cooling system and then tighten the radiator cap before turning the engine on. You can then proceed to turn on the air conditioner which will increase the load on the coolant system. You can drive your vehicle for a few minutes and then check the engine components to find the leakage.

Warning: You should never open the cap of your radiator when the engine is in hot condition. This is because the cooling system will have a very high-pressure point. And when there is an actual leakage on the system, the coolant is possibly boiling inside the engine. One way to do this is to let the engine cool down after letting it sit for about an hour. You can then slowly open the radiator cap to release the pressure little by little. You can proceed to take the cap off until all the pressure has been vented.

You can also employ a special pressure tester that can determine the condition of your cooling system. This tool is a simple hand pump that combines a vacuum gauge and pressure gauge and can be attached to the radiator filler neck. If the tester detects that the system can hold a stable pressure point for about 15 minutes, then there are no leaks in the system. Meanwhile, if the pressure point is constantly dropping, there might be leakage on the system. If you cannot inspect the leaks visually, the leakage might occur internally.

A leaky condition on the head gasket can also be inspected using a block checker. This tool will use a blue liquid that is sensitive to other gases. The liquid will be able to change color when it reacts to combustion gases produced by the coolant system.

Using colored dyes can also be a good way to check leakage on the coolant system. These dyes are usually bright-colored and can react when exposed to ultraviolet light.

Checking the Radiator Cap

If the system is experiencing frequent overheating, you might need to check the pressure point on the radiator cap. This is important especially when you experience coolant leakage with no obvious leaks. If the radiator cap is weak, it will not be able to hold a stable pressure point which will lead to the system overheating. You might need to replace the radiator cap if it has no ability to hold normal pressure points.

Radiator Cap Checks

How to Repair a Leaky Radiator

There are several methods on how to fix a leaky radiator. These methods include:

One method is to add a sealer product to the radiator. This is an easy and cheap way to fix the coolant system. Most of these products are developed to fix small leaks. Some products are also effective to seal internal engine leaks. But, this is usually just a temporary solution for your leakage problem.

Another method is to repair the condition of the radiator. You can usually do this on radiators that are made from copper or brass material. But, if the components of the radiator have corroded or damaged too much, you might not have an alternative other than replacing it with a new radiator.

How to Fix a Leaky Heater Core

Adding a bottle of sealer product is also a choice to fix a leakage on the heater core. The sealer will usually be effective if the leakage is small and temporary. But, if the sealer product is still unsuccessful in stopping the leakage, another step is to take apart the AC case and replace the heater core components. This is usually a very complicated job that will require expert knowledge of the components.

There are some vehicles that have design problems on the heater core due to the material that was used to build the component. But usually, the most common cause of leakage on the heater core is electrolysis corrosion. The alternative to fix this is to connect the heater core to a grounding strap. You might also want to replace the stock heater core with one that is made with copper or brass material.

Coolant Reservoir Leaks

The coolant overflow reservoir is also another component that commonly gets leakage from the cooling system. This component is usually used to catch the coolant overflow from the radiator but is also designed for other uses. The reservoir can store excess coolant that escapes the system. Normally, the mechanism will force the hot coolant out from the radiator pressure cap to get into the reservoir. When the engine cools down, the drop in pressure point will draw the coolant from the reservoir to the radiator.

If your vehicle is a new model, this component is usually pressurized and is a very important part of the coolant system. The reservoir tank is also the location of the cooling system filler cap that is connected using hoses from the radiator to the engine. This component is made from transparent plastic and will allow you to see the coolant level inside the system.

If there’s a leakage on the coolant reservoir, this component will let the coolant seep through when the engine is being operated. Over time, the lack of coolant will occur, and the engine will frequently overheat.

You can probably use a silicone sealer product to repair small leaks or hairline cracks in the overflow reservoir. But, if the condition of the reservoir requires replacement, you should also pay attention to the installation of the hoses so they can connect the reservoir to the radiator. Make sure that the hoses are free from anything that can block the coolant to flow freely between the components.

Fixing a Leakage on the Freeze Plug

Freeze plugs are the components that are designed to prevent the coolant from freezing when there is not enough antifreeze in the system. This component is made from metal and is pressed onto the cylinder head. Corrosion can occur on this component which can result in coolant leakage and frequent overheat on the engine.

One alternative to fix this component is to sand the surface down with sandpaper. You can then proceed to apply a two-part epoxy to the component. This method will be able to seal the leakage on the freeze plug if you let the epoxy properly cure overnight.

You can also try to replace the damaged freeze plug by knocking out the old component. You can do this by pounding the sides of the plug which will cause it to twist. Proceed by prying out the component with the help of a large screwdriver. Replace the new plug after cleaning the hole and applying a generous amount of coating on it. Make sure that the new plug is in a straight position to ensure a good sealing capability.

Another alternative is to use the help of an expandable freeze plug. This component is usually easier to install and will have less possibility to experience leakage.

Fixing a Leakage on the Coolant Hose

If the leakage occurs on the radiator or heater hose, your only option is to replace the damaged hose with the new one. This is because sealer products will not be able to properly seal the damages on this component. Make sure that you check the condition of other hoses because the damage on one hose is usually an indication of damage conditions on the others.

Radiator hoses are usually difficult to remove since they stick tightly on their fittings. You might be able to cut off the hose using a razor blade to free the component from the fittings.

If your vehicle uses a ring-type for the hose clamps, one good alternative is to replace the original one with a component that is made from stainless steel. Make sure that you only use stainless steel components that are made from high-quality material so you can use them for a prolonged time.

Electrolysis corrosion can also cause deep cracks on the radiator and heater hoses. You should always inspect the inside part of this component after you have successfully removed it from the engine. This condition is usually the result of contaminants in the antifreeze that you use for the coolant. Another possibility is from the stray electrical currents due to the high contaminants on the cooling liquid.

Car Cooling System

Fixing a Leakage on the Water Pump

You can only replace the water pump if the leakage happens on this component. The sealing product will not be able to properly fix the damages to the water pump. But, if new water pumps are too expensive for you, you might be able to opt to get a refurbished water pump to save some money.

On most engines, the job to replace the water pump can be done relatively easily. The trickiness might come from the fact that the water pump uses a timing cover to hold it in place. An improper installation method can possibly break the sealing capability of the timing cover which will result in a coolant leakage to escape into the crankcase. Some manufacturers recommend the usage of special tools for a replacement that can hold the timing cover in place when you uninstall the old water pump.

You should also check the condition of the fan clutch while you are trying to uninstall the water pump. The condition of the fan clutch is usually similar to the water pump, in which you will need to replace both components at the same time. If you can notice wobbling or leaking on the fan clutch, this component will also need to be replaced immediately.

How to Refill the Cooling System

After repairing and replacing the components from the coolant system, you will also need to refill the coolant back. For this, you have to properly mix antifreeze and water with a 50-50 composition. Using straight water will result in the inability of your engine to have corrosion protection. It will also lead to an easier overheating condition for the engine. You can refer to the vehicle’s manual to get information on the type of antifreeze that you need to use. Normally, newer vehicles require you to use long-life OAT or HOAT coolant.

If your vehicle is the newer model equipped with a front-wheel driving mechanism, you might need to open the bleeder fan before refilling the cooling liquid back into the system. This will be able to release the trapped air in the system before inserting the new coolant. If you don’t do this, your vehicle engine might experience overheating when you drive it for the first time.

One piece of advice that you need to follow when you are refilling the coolant system is to add the coolant liquid until there is only an inch of space left in the radiator. You should also add coolant to the reservoir tank following the proper level from the vehicle’s manual. If your vehicle is equipped with a pressurized coolant reservoir, you will need to insert the coolant liquid up to a mark that says COLD FULL on the reservoir.

You can then proceed by turning on the engine and letting it idle for a few minutes until the coolant starts to move and circulate inside the engine. You should also turn the heater on to push the coolant to circulate and reach the heater core. If you notice the coolant level is dropping, you can continue adding the coolant liquid until the system can no longer take more. You can then drive your vehicle for a few minutes before turning the engine off and performing a recheck on the coolant level. If the level is low, add a proper amount of coolant until the system is full again.