Why You Observe Steam Coming From Radiator Cap?

Traveling is the most loved part of everyone’s life. After all, we all have hidden gallivanter inside us that enthusiast us, encourage us, and motivate us to do adventures and face challenging life.

Road journey or car with concave mirrors accompanied by smooth wind and soothing atmosphere along with greenery all around, but suddenly your car betray and observes steam coming from radiator cap. This situation spoils your mood, but it’s a big issue in the places where there is no garage or service center nearby.

Thus, we are here to ease your problems and help you out in such cases. Let’s have a brief discussion on how to deal with such a situation, i.e., its signs, causes, and what to do in such cases.

What Do You Mean By Radiators?

The radiators are heat exchangers and the central part of the engine’s cooling system. It maintains a cool environment and prevents the heating of the engine while driving the vehicle. The antifreeze mixture and water runs through the radiator and absorbs the engine’s heat, thus providing a cooling effect. It is mainly present in automobiles and available in motorcycles, piston-engine aircraft, railways, and power generating plants. Automobile radiators usually manufactured from a pair of metal or plastic header tanks linked by core.

What is White Smoke Or Steam In Cars?

White smoke or steam develops as a result of normal condensation generated inside the exhaust system. Steam from the car is seen or observed when the vehicle’s cooling system fails or faces any fault. The faults can be related to the damaged cylinder head, leakage of coolant, or overheating of the engine.

Signs Of A Faulty Radiator Cap

When the pressure on the vehicle exceeds the maximum value meant for the cooling system, then this fails in the cooling system; thus, we observe steam coming from radiator cap. Although there are various ways to determine faulty radiator caps but most often used techniques are:

1. Leaking Coolant

If the radiator cap is stuck, it will result in pressure build up inside the radiator, causing it to burst. If you observe coolant near the radiator cap or holes near it, it signifies coolant leakage.

2. White Streaks On Radiator

If we notice white streaks near the radiator, it’s definitely because of the coolant leak out of filler, thus confirming faulty radiator caps.

3. Overflowing Reservoir

The coolant expands as it reaches the reservoir tank, and the extra pressure generated because of this passes into the overflow tank with the help of a radiator cap. Thus, if we have a faulty radiator cap, then it would result in reservoir overflow.

4. Radiator Hose Bursts

Generally, when the pressure in the cooling system exceeds too much, this would result in a burst of hoses; however, in initial conditions, the hoses try to compensate for the increasing pressure by spraying coolant all over the engine bay.

5. Overheating Engines

Leakage of coolant or air in the cooling system may result in overheating of the engine. If you observe the steam coming from the radiator cap, allow the engine to cool for some time and then drive; otherwise, it may damage the radiator cap.

6. Air Inside The Cooling System

If your radiator cap is not adequately sealed or fixed, the air would enter the cooling system and interfere with its functioning, resulting in an overheating engine.

What To Do When Steam Coming From Radiator Cap?

First of all, don’t panic and be calm. It is a usual phenomenon caused due to failure of cooling system of the car or faulty radiator cap. So, try to follow the steps given below if you face such a condition.

Step 1:  If You Observe Steam, Then Pull Over Immediately

If you notice smoke coming from your radiator, then the reason is overheating of the engine. Condensation might not be observed or seen in plumes, but it appears in traces.

Step 2:  Turn Off The A/C, And Turn On The Heater

Generally, we follow this in older cars, as they heat up very often on hot sunny days and may need a breather. So, this is achieved by turning off the air conditioner and switching on the heater.

Step 3:  Pullover And Switch Off The Engine

To avoid further complications, immediately shut off the engine roadside in proper space, as this would prevent the engine from overheating anymore. It is better to find roadside assistance too.

Step 4:  Allow The Engine To Cool And Open The Hood

Give an appropriate time for the engine and engine’s hood to cool, then only open it. You are requested to be quite careful while opening the engine’s hood as safety is our priority.

Step 5:  Check The Coolant Levels

After ensuring that your engine is cooled off, check the coolant reservoir level according to your owner’s manual.

So, if you notice that your coolant level is average, you may have no damage to the engine, i.e. your engine is refined. But if you observe that your coolant level is low or empty, it might be a coolant leak, which is quite challenging to do yourself and thus needs a repair in a garage.

Step 6:  If You Still Want To Continue Driving

The option left is that wrap a piece of cloth or towel around your hands and remove the radiator cap. It must be initiated or performed when the engine is completely cooled off. Now refill the radiator with coolant and if you lack or do not have coolant, then use water.

Don’t forget to fix the problem permanently as soon as possible by visiting the service center.


So, one must be clear that steam coming from radiator cap is not as simple as we see in movies or fantasy world. It is quite a problematic and challenging situation which one faces. I hope our article helped you in finding the answer to your question.

If there is any doubt related to the topic, we are always here to help you out; comment below, and we’ll answer as soon as possible.

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