The most common cause of blue exhaust smoke is oil leaking past engine seals and into the cylinders where it then mixes and burns with the fuel. This is most frequently seen in older or high mileage cars with worn seals and gaskets. It only requires a very small amount of oil leaking into the cylinders to cause excessive blue exhaust smoke.
Blue exhaust smoke only at start-up can indicate worn piston seals or damaged or worn valve guides which may also cause a rattling noise. An external engine oil leak can drip onto hot engine and exhaust parts causing what appears to be blue exhaust smoke. Other possible causes of blue exhaust smoke include: piston wear, worn valve seals, a dirty or non-functioning PCV valve, worn piston rings, an intake manifold gasket leak, worn engine oil seals and possibly even head gasket failure.
Oil leaking into the cylinders can cause a rough idle, misfire and fouled spark plugs. In addition, a reduction in power and oil loss can be indicators that the blue exhaust smoke is caused by an internal engine oil leak. Internal engine oil leaks can also allow fuel to mix with the oil in the crankcase which will degrade the oil and prevent it from adequately protecting the engine.
Operating a car with a severely dirty oil filter, air filter or improperly functioning PCV valve can also sometimes result in engine oil blow-by, oil loss and blue exhaust smoke. Periodically checking the engine oil level with the oil dip stick will indicate if there is excessive oil consumption. Higher viscosity engine oil can sometimes temporarily reduce the amount of blow-by; however, this is not generally recommended. Excessive blue exhaust smoke indicates a possible internal engine oil leak that should be inspected by an ASE certified mechanic.
Related Questions and AnswersWhat is the Average Price of a Piston Ring Replacement?
Piston ring replacement is called for when your engine is losing compression into the crankcase, or you have oil from the crankcase leaking into the combustion chamber. Exactly how much you will pay for this job will depend on how many cylinders your engine is equipped with, and how many cylinders need ring replacement. Also, if you choose a bare minimum repair. For a four cylinder engine, where you replace the rings on all four cylinders, you can expect a minimum of 4 hours worth of labor. With an average labor rate of $80/hour, that will translate into a minimum of $320 in labor alone.