What Are The Main Radiator Cap Leaking Symptoms?

Are you suspecting that your vehicle’s radiator cap is faulty? You may be trying to find some methods or signs that may be indicating such an issue. For that, you should know what are the signs and symptoms your car shows when your radiator cap is faulty. This article tries to analyze the different radiator cap leaking symptoms your car shows. This will let you know that it is suffering from such an issue. Thus, read on to find if your car’s radiator caps are faulty. 

What Is The Importance of Radiator Cap?

Most of you may have a clear idea of what a radiator cap is. You may have at least heard about the existence of such a thing in your car. The part of the vehicle which is commonly known as the radiator cap has 2 valves. The purpose of a radiator cap in your vehicle is to contain the coolant in the radiator and ensure that the cooling system stays pressurized. 

Cooling systems hold different amounts of pressure but mostly it is found to be somewhere between 13 and 16 pounds of pressure per inch (PSI) or in the neighbourhood of 1 bar. This pressure is usually controlled by the radiator cap and needs to remain constant. 

Too much pressure will be more than the manufacturer’s specifications for the cooling system which will cause system component failure. and too little pressure can cause the coolant to boil off. This will result in the overheating of the engine as there will be no liquid around to cool the vehicle. 

What Are The Main Radiator Cap Leaking Symptoms?

Mainly, there are about 7 major radiator cap leaking symptoms that you need to be aware of. Below all of the 7 are discussed in detail to help you identify a faulty radiator. 

1. Leaking Coolant

If your vehicle’s radiator cap is stuck, pressure will be built inside the radiator of your car. This would result in the contents of the cooling system or the coolant, to leak or burst. If you are noticing coolant leaks anywhere near the radiator or under your car, you can conclude that there is some issue with your radiator cap. Some other issues can also cause radiator leaks, but checking if the radiator cap is alright among others, may come in handy to you. You have to check whether there are any holes in the radiator or if the radiator cap is worn or damaged. If so, take the necessary steps to get the cap replaced. 

2. White Streaks on Radiator

Sometimes coolant leaks out of the radiator filler and dries out in the neck. These dried-up portions will leave a white streak-like mark. These leaks are caused because of a faulty radiator cap. So if you notice the appearance of white streaks on your radiator, all of a sudden, then you can conclude that your radiator cap is bad. 

3. Overflowing Reservoir

Coolant goes into the reservoir tank of your car as it expands. The radiator cap usually releases its pressure by sending some coolant into the overflow tank. However, if your radiator cap is just too bad, the coolant might get released too quickly, causing the reservoir to overflow. Thus if you notice that your coolant overtake is overflowing, you can conclude that as one of the radiator cap leaking symptoms. 

4. Radiator Hose Collapses

A faulty radiator cap is one of the reasons if your radiator hose collapses. The vacuum will be released wrongly if the radiator cap is faulty which causes the radiator cap to collapse during the cooling down period. In such a situation, check the condition of your radiator cap and get it replaced soon if you see that it is faulty.

5. Radiator Hose Bursts

If the pressure in the cooling system gets too high, one or more hoses might start to spray coolant all over the engine bay. The pressure may not be high enough to rip the hose in half most of the time. You can find pinpoint leaks that only spray the coolant when the car is warmed up. A hose with a small hole may seal just fine when the car is cold. As you drive, pressure in the cooling system will build. The pressure will eventually be enough to force coolant through the tiny hole and your car will slowly lose coolant. 

You may be able to notice leaks under your car on the ground or in the engine bay in such a situation. Check to see if your overflow reservoir is draining slowly throughout a few miles. This may give you a hint that this is the problem.

6. Overheated Engine

Leaking coolant in the cooling system, which is one of the radiator cap leaking symptoms, can lead to an overheated engine. If you notice your engine starting to produce steam from getting too hot, make sure not to look under the hood without turning the engine off. Then only check under the car’s hood after letting it cool for a while. This would let the engine cool off for a while while you are checking the engine too. If you notice that there is coolant fluid near the radiator cap it means that there is damage to the pressure cap. Check for that and replace it by having it checked by a mechanic. 

7. Air Inside The Cooling System

If your radiator cap is faulty, it won’t be able to seal properly. This would let the air easily enter the inside of your car’s cooling system. This will cause air pockets to get inside the heater core, thermostat and radiator hoses. This will cause the engine to overheat as it won’t be able to sustain a consistent temperature. 


The radiator cap is one of the most important parts of your car’s radiator. Radiator plays a very important role in keeping your cooling system in top condition and having a faulty radiator cap is not at all desirable. All the different signs and symptoms that your car shows when your radiator is faulty are discussed in this article to help you get a better understanding of the situation. Hope you found it helpful!

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