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Common Cooling System Problems

29/Nov/2023 145 |

The cooling system problems can be detected by one of two ways:

  • You find a leak in your driveway
  • The engine starts overheating.

The cooling system is not maintenance-free and requires regular checks to stay in good condition.


There are a lot of flexible connections in the cooling system and this is where leaks most commonly start. The rubber hoses will begin to wear out and the joints will loosen from movement. A leak can happen anywhere in the system: the water pump can leak, the radiator can rust through, or the cylinder block can lose a gasket. Leaks in hoses can usually be repaired easily, but leaks in big components like radiators and water pumps generally require the attention of a professional. Leaks that aren’t addressed can lead to overheating, which leads to engine failure. Get a leak repaired right away.


The coolant in the radiator is mixed with water, and the water can bring with it minerals and deposits that will clog and corrode your radiator. When this happens, the coolant can’t pass through the tubes of the radiator, and the engine overheats. If it rusts out, it will eventually drain down and cause overheating.

A mildly corroded radiator can be flushed with commercially available products, or some pros offer a power flush that really gets the radiator clean.


The water pump is subject to failure in several ways.

  • A mechanical pump that is mounted to the engine may fail at the gasket points where it connects to the engine.
  • it may stop working if the engine belt driving it slips or breaks.
  • An electric pump may fail if its internal motor dies.
  • The bearing in the water pump can also give out.

A whining sound may indicate that a water pump is about to fail.


The thermostat is responsible for regulating the flow of coolant by measuring the engine temperature and opening if the engine needs to be cooled down. If the thermostat fails while closed or partially closed, the car will overheat because the coolant can’t flow. If the thermostat fails while open, it will take the engine a much longer time to come up to temperature, which can be hard on the oiling system and cause oil crystallization on the engine components. Don’t run your car without a properly functioning thermostat.


Coolant needs to be topped off or replaced periodically. You can check the level and condition of the coolant in the overflow tank. If the level is low, it can be “topped off ” with distilled water. If it’s getting brown with contaminants or rust, it’s time to change the coolant.


Hose clamps usually don’t fail unless they have been removed and reinstalled. Be careful when reinstalling hose clamps that have been stretched — they can fail on reinstallation.

Locating Leaks

Leaks in the cooling system can be internal or external. Internal leaks, where the coolant is getting into the cylinders and oil pan, can cause serious problems and should be addressed by a professional. External leaks might be easily repaired depending on where they are located.

Here are some ways you can locate a leak in your cooling system.

  • Use a piece of cardboard. If you suspect you have a leak but aren’t able to locate the source, place a piece of clean cardboard under the engine area of your car when you park it for the night. In the morning, the position of the liquid on the cardboard should help you find the leak.
  • Inspect the hoses. Rubber components, like the hoses, can often develop leaks since they are designed to flex. Wearing surgical gloves, gently run your hands around the cold engine and feel for leaks on the back sides of the hoses. Check the hose connections and make sure the hoses are tightly held in place. Also, check for rusty water or stains on the hoses. As you go, check your gloves for the fluorescent color of the coolant.
  • Inspect the radiator. The radiator is made of thin metal fins, which can easily be punctured or rusted. This radiator suffered from a cooling fan that dug into the middle of the radiator fins. Corrosion or mineral deposits due to damage could be a sign of a leak.
  • Inspect the radiator cap. The rubber seal in the radiator cap can fail, and the metal backing holding the seal can crack and allow pressure to be released. When the engine is cool, inspect the area around the radiator cap for signs of escaping coolant. Remove the cap and inspect the underside. Look for a milky, oily substance—this may be a sign of an internal coolant leak.
  • Check the heater core. The heater core is located inside the passenger compartment, and if it starts to leak, it may soak the carpeting with coolant, or it may weep out of the air conditioner drain. If the inside carpet is getting wet, blot it with a clean paper towel and look for coolant color or rust.
  • Check the thermostat housing. Some thermostats are mounted on the top of the engine where the hot coolant is returned to the radiator, and this is a key area for leaks. You can see evidence of a past leak here from the mineral and rust buildup on the aluminum housing and the re-positioned hose clamp.
  • Inspect the engine block freeze plugs. The engine is equipped with something called freeze plugs, which pop out if the water in the engine begins to freeze and expand. These freeze plugs can rust out or weep. Look for signs of rust trailing down from the freeze plugs.
  • Check the head gaskets. There is a gasket between the cylinder block and the cylinder head made of metal. If it fails, coolant may flood into the cylinders or it may leak out the side of the gasket. When this happens, you may see a small stream of fluid running down the length of the engine.
  • Check the water pump. A water pump failure can happen at the gasket between the pump and the engine or at the front bearing on the rotating shaft. The water pump may have something called a weep hole, which is a hole near the rotating shaft. This weep hole is used if the water pump is beginning to fail. If the weep hole is leaking oil, it means the front bearing is failing. If it is leaking coolant, it means the seals in the pump are failing. If you see anything coming out of the weep hole, have it checked right away.
  • Check the oil. Remove the engine oil dipstick and look for a white, milky substance. This is a sign that there is an internal engine leak and you need to have it checked.
  • Pressure test the system. Use a radiator pressure tester to test the system. This is a small pump and gauge that attaches to the radiator in place of the cap. Bring the cooling system up to pressure and monitor the gauge for a couple of minutes. If the system doesn’t lose too much pressure, there aren’t any serious leaks. A quick drop of pressure may confirm an internal leak that you can’t see. 
Global Spare Parts, Oman

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