fume leakage
How do exhaust fumes build up inside a car?
Points of leakage
Exhaust can leak from any point of weakness inside the engine or exhaust system: these include the head gasket, the manifold, the catalytic converter and the muffler. Exhaust can also enter and damage the cooling system, causing further leaks.
Fumes, once escaped, can enter the car through openings that form part of the car design (such as air inlets), or through those that arise due to wear and tear, including broken or loose bulkhead seals, holes in the floor or panels, welded joints that have experienced fatigue, faulty HVAC systems, and defects in the boot seal.
But doesn’t the catalytic converter soak up all the CO?
Catalytic converters cannot remove CO from a leak that occurs upstream. Catalytic converters, furthermore, are designed to work at hot temperatures. Stop-start driving, especially on short journeys and at low speeds, prevents the catalytic converter from operating fully.
It is also worth keeping in mind that car exhaust contains many other toxins besides CO. These include nitrogen dioxide, sulphur dioxide, benzene, formaldehyde and particulates.
But if a car passes its emissions test, doesn't this mean it is safe?
An emissions test checks what is in the exhaust: it does not check where the exhaust gases are going. Regardless of whether they comply with emissions limits, gases leaking into the passenger cabin will cause harm to health.
Can a garage check the exhaust for leaks?
It is important to have your exhaust inspected regularly. However, a garage check cannot detect points of leakage large enough to affect your health, but too small to see or measure.
Is this just a problem with old or badly-maintained cars?
No. While wear and tear increases the likelihood that a car will develop a fume leak, CO leakage can occur in cars of any age.