Why is my engine coolant bubbling?

Bubbles in the cooling system of a vehicle, however rapid or slow-moving, can be a sign that exhaust gasses are escaping the combustion chamber inside the engine. This can create what we refer to as ‘backpressure’, which is one of the common signs of a blown head gasket.

How is back-pressure caused by a blown head gasket?

The head gasket is an engine component which acts as a seal between the combustion chamber and the cooling system, keeping the highly compressed gasses in the combustion chamber away from the completely separate cooling system.

When a head gasket is blown, the seal is broken, and the highly compressed gasses can escape into the cooling system.

This means the coolant passages, which are only built to handle the maximum water pressure expected in the cooling system during normal operation, are exposed to highly compressed gasses escaping and circulating within the system.

Why should I fix my blown head gasket?

Bubbles in the cooling system (or back-pressure) are a tell-tale symptom of a blown head gasket, which brings other problems which can eventually result in a complete lack of compression in the engine and the vehicle being unable to start.  Although a blown head gasket is a serious issue, like many faults, the sooner you spot the problem and seek advice, the less chance you have of causing catastrophic damage to your vehicle.

Coolant Leaks

Once the exhaust gasses escape into the cooling system, the comparatively fragile system has to contain much higher pressures than it was designed to. This can cause splits and holes in the cooling system, often the expansion tank or radiator, resulting in coolant leaks which can contribute to the vehicle overheating and the head gasket sustaining further damage.

Compression Loss

The gasses inside the combustion chamber are operating at high compression levels; the optimal function parameters for the necessary reactions inside the engine. As these gasses escape into the cooling system, the pressure inside the combustion chamber reduces, compromising the effectiveness of the reactions in the engine and eventually preventing it from being able to start at all.

My car has back-pressure. What should I do?

If your vehicle’s coolant is bubbling, it is highly likely that your vehicle has a blown head gasket. Take the vehicle to a mechanic for an official diagnosis, and research your repair options, such as using Steel Seal or a mechanical repair if this is viable for your situation.

Safety tip

Be aware that strong back-pressure can result in coolant being splashed out of the expansion vessel. This coolant can be extremely hot and could cause severe burns. Therefore, take care when working within the engine bay and removing expansion/radiator caps to avoid potential burns, in particular to the face, and hands. If you believe there is back-pressure, do not get your face too close to the expansion vessel, and consider wearing personal protective equipment such as eye protection and gloves.

I am using Steel Seal and I have backpressure, what should I do?

If attempting a repair using Steel Seal, be sure to follow the additional directions for backpressure.