Smell of Gas in a Radiator

by Chris Weis

    Automotive engines need a cooling system to reduce the heating effects effects of internal combustion. This combustion generates extreme heat, which the cooling system must regulate to preserve the function and structure of the engine. Though the purposes of the combustion chambers and cooling system are inexorably coupled, their separate atmospheres must never combine. The smell of gasoline, or exhaust fumes, in your radiator is just cause for alarm. You may prevent further engine damage by taking action at the first recognition of this serious symptom.

    In liquid-cooled engines, an outer compartment is cast into the engine block to circulate the liquid, which envelops the cylinders. This area is called the "water jacket," and it is sealed off from the combustion chambers inside the cylinders. The liquid coolant also flows through passages in the cylinder head. The head houses the engine valves, and is mounted above the combustion chambers. Coolant circulates through the radiator, to the engine water jacket and through the cylinder head. A gasket seals the engine passages that allow coolant from the block to reach the cylinder head. This "head gasket" is the most vulnerable component of the structure.

    Airflow across the radiator exterior reduces the temperature of the liquid coolant inside. Coolant in the radiator is exchanged with the contents of the engine water jacket repeatedly, in normal operation. A faulty head gasket can allow fuel or combustion gases to force their way into the engine water jacket. Contaminants, like gasoline, flow from the engine, and emerge in the radiator. When gasoline dilutes the coolant mixture, it compromises the coolants protective qualities. Components of the cooling system, like water pump seals or gaskets, may also be adversely affected by the contamination. Any resulting leaks can further detract from system performance. Although serious in nature, these defects might be secondary concerns.

    The head gasket not only seals coolant and oil passages, but also isolates the cylinder combustion chamber. Breaks in the gasket might allow the two liquids to mingle, or enter the cylinder. The pressures that form during the cylinder combustion process can pass through a breach in the head gasket. This pressure leak commonly results in loss of combustion in a cylinder. Fuel persists in a liquid state, without combustion, and can enter the water jacket through the leaky gasket. Conversely, the vacuum that the piston's intake stroke creates may be draw coolant into the cylinder. When an engine attempts to burn trace amounts of coolant, clouds of white smoke teem from the exhaust tailpipe. Unfortunately, coolant entering a cylinder can be even more eventful.

    Piston travel can be halted by a column of liquid in a cylinder. A piston normally compresses a mixture of air and atomized fuel near the top of its stroke in the cylinder. Liquids in volume cannot be compressed, however, and the piston stops short. The remaining pistons, and the engine crankshaft, continue to move, albeit briefly. These contrary actions usually cause something substantial to break. The top of the piston may shatter, or the rod that connects the piston to the crankshaft can fracture. Fragments of broken parts can ruin adjoining surfaces, or interfere with other moving parts. In extreme circumstances, internal engine parts can erupt through the engine block. Either way, the engine is usually damaged beyond repair.


    • Basic Car Care Illustrated 2nd Edition; William Flerx, et al

    Photo Credits

    • front of antique car image by Xavier MARCHANT from