Knocking out of the blue, small oil leak developed, what, why..this is not right!

Asked by Oct 08, 2016 at 03:57 PM about the 2003 Buick Century Sedan FWD

Question type: Maintenance & Repair

2003 Buick century 3.1 L ..95,000mi/one owner/.purchased with75,000mi
Follow closely....
2weeks prior..ran over softball sized rock in roadway..oil pan / no damage but had to replace trans pan/punctured ... at this point, all is good once again.
Yesterday, without warning..loud, lower end knocking along with a oil leak,minor in volume from just above oil pan lip, 3-4 " from harmonic balancer/pulley back side of motor...instantly/obviously performance bottomed out, engine light FLASHING, and an ODOR similar to cat. converter/ unburnt fuel??
..upon inspection after towing, adjacent to pass side tri-hub housing @ oil small piece casting? from ext. of pan..No visible cracks, no rod hanging out..My latest thought..a delay in damage??from rock hitting trans pan..and oil pan lip..chipping small metal into the oil from inside of block giving way to the KNOCK...ya , a headache I fluids visible contamination/oil remains clean as usual.  WhatYa Think?????

2 Answers


The noise may not be related to the rock........ A fairly common noise producer is a harmonic balancer that is coming apart. Pull the belt off the accessories and feel the harmonic balancer should be solid, little play, it it moves radially or side to side it is probably shot. You can also start the engine (preferably when cold) with the belt off and see if the noise is gone.


The flashing check engine light is warning you that the engine is misfiring and damaging the catalytic converter. The odor is the converter getting hot because of the unburned gasoline being dumped from the misfiring cylinder. You'll have to find out which cylinder is misfiring and find out why. I also doubt it's from the rock. HTH. -Jim

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