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Buying a Used Car: 6 Vehicle Warning Smells Could Be a Cause for Alarm

Finding the car of your dreams — or simply tracking down a new daily driver — involves patience, lots of tire-kicking and some detective work. Beyond the obvious signs of disrepair or poor maintenance, there are certain vehicle warning smells that can provide clues to ongoing or potential problems. The following smells are the most commonly sniffed odors that can signal trouble:

1. Oil

Oil is the lifeblood of your engine. A hot or burnt oil smell could mean that oil is leaking onto the exhaust system or another hot portion of the driveline. Oftentimes an unscrupulous seller will wipe down leaking areas. Beware of clear, clean shiny parts on the engine or drivetrain. To verify a leak, check for oily patches on the pavement or parking area under where the vehicle was stationed. In addition to a burnt odor coming from under the hood, look carefully for smoke coming from around the engine or beneath the vehicle.

2. Burnt Rubber

The scent of burning rubber could mean a slipping drive belt or a loose hose rubbing against rotating accessory drive-belt pulleys. Check the tension of exposed belts and look for uneven wear, cracks or missing chunks of the belt. In older cars, check to see if a vacuum hose is resting on the hot engine block. Make sure that the engine has cooled off prior to checking all hoses!

3. Gasoline

A raw gasoline smell is likely a bad gas line, bad fuel injector line or a leaky gas tank. This is not a minor repair that can be ignored or taken care of with a quick fix. The smell of fuel indicates a potential ignition hazard, so an immediate repair should be requested. If you’ve ever witnessed a single car on the side of the highway engulfed in flames, the culprit was likely a fuel leak.

4. Heating and Cooling

A sweet or maple-syrup-like smell indicates that the car is leaking engine coolant, the heater core has failed, or another component of the car’s cooling system has been compromised. The scent is usually faint at first before getting progressively worse. Checking the coolant level after the first whiff of syrup is key to knowing the severity of the leak, particularly if it is not readily visible (make sure that the engine has had time to cool before removing the radiator cap!). Depending on the severity and location of the leak, there are products that can temporarily lessen or pug the leak, but they won’t solve the problem for good.

5. Bad Brakes

Another burning smell resembling plastic or carpeting could be an indication of brake trouble. Check for visible leaks at the master cylinder and try to pinpoint where the smell is coming from. Address this issue quickly and firmly with the seller, and insist that the brakes be checked right away, as this could end up being a very costly repair. This is an especially worrying issue if the smell is more pronounced during or immediately after normal driving conditions.

6. Other Odors

There is no mistaking the smell of rotten eggs. This smell could represent something as minor as a bad tank of fuel, but it’s more likely an indication that the catalytic converter is not properly converting hydrogen-sulfide exhaust to sulfur dioxide. Getting a new converter isn’t cheap: I recently priced a replacement converter for a compact 11-year-old import sedan, and the range was $900 to $1,200, including labor.

Be Aware

If you detect one of these vehicle warning smells during your test drive or inspection of the car, determine the severity of the problem and how much it will cost to repair it before you make a purchase. As with all used-car purchases, we suggest that you take any prospective vehicle to a certified mechanic for inspection before deciding to buy.

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  1. I have a 2 year old Merc E550 with only 5K on it. Since I acquired, it has had a bad burning smell coming from under hood. Cannot smell in the car. I was told that the car was new and still burning off things and this was normal. Almost one year later, it smells more like burnt maple syrup and the smell is NOT going away. Car is in shop and I am told they can find nothing wrong. Extremely concerned that they WILL find somethign wrong when car is out of warranty, which is 2 years away. The car has not been overheating. Temp gauge usually goes up to about 3/4. 

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