What Might That Smell Mean?

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You can guesstimate with some accuracy what might be wrong with your car just by using your nose. If you’re hip to what various smells suggest. Let’s have a look – or rather, a whiff!

* Rotten egg smell -

This is indicative of a problem downstream – in your car’s exhaust system. The egg smell derives from sulfur, and is byproduct of the combustion process. To be precise, it is a byproduct of an overly rich air-fuel mixture, which in a modern car is often caused by a problem with the oxygen sensor located in the exhaust piping upstream from the catalytic converter.

The O2 sensor samples the chemical composition of the exhaust gasses and sends a signal to the engine’s computer controller, which in turn maintains an optimum air-fuel mixture. But when the 02 sensor is not working properly, the result is sometimes too much fuel in the mix (a “rich” condition) and – in a car with a catalytic converter (which is every car made since 1975) –  the result is often that stinky sulfurous smell.It’s important – if you want to avoid a big bill – to get the car checked out as soon as possible, because running it in this condition may cause the converter to overheat, which can result in the honeycomb lattice inside the converter to melt and fuse, creating excess backpressure – which will result in progressively worse performance and declining gas mileage.

Be advised that replacing just one tits up catalytic converter can cost a couple hundred bucks. And many new cars have two – or more – cats.

* A sickly sweet smell – 

This is usually leaking (and sometimes, burning) anti-freeze, also known as engine coolant. The neon green (and in some cars, orange-red) fluid that goes in the radiator. This fluid is used to carry heat away from the engine and radiate the heat – via the radiator – to the surrounding air. It is also used to carry heat into the passenger compartment, to keep you warm in winter.

Places to look for leaks include all the rubber hoses that plumb the radiator (at the front of the car, in most cars) to the engine. There are also hoses that (typically) run from the engine to the cowl area (just below the base of the windshield). These are the hoses (usually, two medium sized ones) that circulate warm engine coolant to the cabin, to provide heat.

The radiator itself is also a potential suspect.

Provided the leak is small – you usually have time to get the problem (such as a leaking hose) fixed before it leaves you stuck by the side of the road. But don’t ignore the problem – or it will eventually leave you stuck by the side of the road. Small leaks can become big ones, in part because your car’s cooling system is pressurized. Lose enough coolant and the car will overheat – and you’ll be calling AAA (NMA, if you’re Libertarian-minded!)

If you smell that sickly sweet coolant smell inside the car, consider it an emergency situation – because coolant is leaking from the heater into the passenger compartment and if not found an fixed, you’ll be dealing with an epic mess that might require ripping out and replacing the carpets. Just for starters. A leaking heater core can ruin your car, which will definitely ruin your day.

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