What is Radiator Cap? | What are Symptoms of Faulty Radiator Cap

The radiator is a major part of the engine cooling system. The cooling system holds a very high pressure (typically 13 to 16 PSI or about 1 bar). A radiator cap uses to control the cooling system pressure. As the cap damages, the pressure leaks that cause insufficient working of the cooling system and engine overheating. This article explains the causes and signs of a faulty radiator cap.

What is a Radiator Cap?

A radiator cap is a mechanical unit that assists to control the high pressure of the hot coolant inside the radiator. This cap adjusts the maximum pressure and prevents the radiator and hoses from being damaged. The efficient working of the radiator cap is very important to control the pressure inside the cooling system.

Radiator cap
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Signs of a Faulty Radiator Cap

As the radiator cap damages or leaks, it produces different symptoms. A faulty radiator cap generates one of the below-given signs:

1) Coolant Leak

The coolant leak may cause due to a bad radiator cap. As the cap clogs, high pressure builds up inside the radiator that may lead to coolant leaks through the cooling system parts.

A coolant leak is definitely present if you observe coolant near the radiator cap.

To determine the cause of the leak, wait for the engine to cool and then tighten the hose that is suspected to be leaking. If you see leakage when you pinch the hose, it means you need to replace the hose.  

The engine hoses have a low cost, and you can easily replace them. After replacement, there should be no more leaks. Air in the system can cause the vehicle to overheat.

2) Overheating Engine

The engine overheating is one of the first signs of a faulty radiator cap. The cap helps the cooling system to maintain the normal temperature of the engine.

The formation of air pockets in the cooling system due to bad seals (i.e., bad radiator cap) or insufficient pressure can overheat the engine. The low pressure reduces the boiling point of the coolant and prevents it from absorbing sufficient heat from the engine.

As you notice a high temperature on the temperature gauge, you must stop your vehicle as soon as possible because it is safe to do so and wait for a few minutes until your engine completely cools.

Engine overheating can cause parts to overheat and begin to crack or warp, eventually leading to engine failure.

3) Steam from Engine

An engine generates steam due to coolant boiling. As the coolant boils, it vaporizes into vapor-like steam. If the engine starts to foam, it means that the coolant is boiling, which is escaping via a bad gasket in the radiator cap.

In this condition, your engine will be overheated very soon.

4) Collapsed or Torn Radiator Hose

The variation in the internal pressure may cause the hose to warp or tear. If the pressure is very low than usual, it may generate negative pressure, which may damage multiple hoses. Overpressure may also cause cracks in the hoses.

During the inspection of the cooling system, you must also inspect the hoses and make sure they shouldn’t be hard or spongy. Spongy lines can collapse, but hard lines are brittle and cannot take more abuse before pressure is applied.

5) Low Coolant

If the refrigerant overheats and vaporizes as a visible vapor, it will not leave the system and will return. If your coolant level is reducing very quickly, it means there is something wrong.  

A faulty radiator cap is one of the main causes of a coolant leak. You must maintain the coolant level up to the recommended level. In a pinch, the coolant level can be topped up with distilled water until the actual coolant can be refilled. In case of a bad cap, you must replace the cap with the new one.

6) Overflowing Reservoir

In case of a faulty radiator cap, coolant can enter the reservoir without the excess pressure activating properly. This may lead to overflowing of the coolant tank or drain prematurely.     

7) White Streaks on Radiator

In case of coolant leakage out of the radiator filler neck and dries, white streaks usually remain under the radiator cap. Take a look at white streaks under the cap to identify a bad radiator cap.

8) Radiator Hose Bursts

The extreme pressure inside the hoses may burst them. As the pressure in the cooling system becomes too high, one or more hoses may start spraying coolant all over the engine compartment.

In the case of a cold engine, the hose with a small hole actually seals tight. During vehicle operation, the engine overheats, and pressure in the cooling system also increases. Ultimately, the high pressure in the hoses forces the coolant to leak through small holes, and the car slowly loses coolant.

In this case, there may be a leak on the floor or in the engine compartment when you arrive at your destination, but not when you start driving.

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