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Sweet smelling exhaust

by Autobytel Staff
October 12, 2009
2 min. Reading Time

There are plenty of smells emanating from your car and some of them are perfectly normal, even if they are annoying. Other odors may be evidence of problems. Some automotive problems are accompanied by a distinct odor. Some odors are only apparent when the car is running, others when it's hot and still others when it's cold. Here's some help in diagnosing some sources of sweet smells in your vehicle that may be a clue to a problem.

A Sweet Smell of Cinnamon

Sometimes a car smells of cinnamon when the air conditioning is running. Being a pleasant smell, it may not always strike you as a problem but, in fact, the sweet smell can be a result of boiling antifreeze. Antifreeze that is leaking into the combustion chamber can produce a cinnamon-type smell, possibly because of a bad head gasket, or cracked head that allows fluid from the cooling system to be drawn into the combustion chamber.


A Sweet Smell of Butterscotch

If your vehicle smells like butterscotch, a minor coolant leak somewhere in the cooling system can be the culprit. Another possibility is that hot coolant is escaping onto the hot engine block which can make the smell even stronger.

 Photo by Wikimedia Commons

Photo by Wikimedia Commons

A Sweet Smell of Maple Syrup

As above, a minor coolant leak can cause the sweet smell of maple syrup. You could also have an internal engine problem, such as a head gasket leaking coolant into a cylinder. If white smoke is blowing out from the exhaust during first 3 minutes of a cold start up in morning and has a sweet smell, stop driving it immediately. It is likely you have a blown head gasket or a cracked/warped head. Serious engine damage can occur if you continue to drive. Lots of white exhaust smoke on start up is a clue to a head gasket problem. If the leak is very small, or leaking into adjacent cylinders, there may not be much smoke upon starting up, and yet still enough coolant may be pulled into the combustion chamber(s) to produce a strong sweetish exhaust smell. Generally, over the long run, this particular problem will continue to produce more engine problems.

 Photo by Wikimedia Commons

Photo by Wikimedia Commons

An Easy and General Leak Check

  • Park your car over a large piece of cardboard.
  • Idle the engine until it is hot.
  • Watch for drips on the cardboard.
  • Have your mechanic check the radiator and hoses for leaks.
  • Check your dipstick for muddy or frothy oil.

A Compression Issue

  • Check the spark plugs
  • Check the oil
  • Check the coolant systems

Check for Coolant Leaks

If no obvious external coolant leak is found at first, checking the above systems for overpressure and contamination can reveal problems regarding the condition of the internal engine.

If the smell is obvious after the engine has warmed or possibly even after it's shut off for a few minutes, the culprit can be a coolant leak, containing sweet-smelling but toxic ethylene glycol. The coolant leak could be coming from a number of places, such as:

  • radiator
  • heater hose
  • a failed intake manifold gasket
  • cylinder head
  • leaky radiator cap

Heater Core

A strong odor inside the passenger compartment can be indicative of a bad heater core. A sweet smell inside the car after the heater is turned on could be;

  • the heater core is leaking and antifreeze is burning and you probably smell it more from the defrost because it blows toward your face.
  • the heater core under the dash is leaking antifreeze.

  • Check the carpet under the dash for moisture. If it is damp, then the heater core is likely leaking.
  • Raise up the carpet and feel behind it for moisture.
  • Check for a film of antifreeze on the windshield that smears and is hard to get off.


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