A quick oil change-with the wrong oil

Mar 1, 2007 by

The insured took his late model sports car to the local branch of a nationally recognized company for an engine oil and filter change. Three months later he brought it in again for another engine oil and filter change.   They used a premium synthetic oil both times.   Two weeks later, the engine failed.   GEI was called in to investigate the cause of the engine failure.

The vehicle was examined at a high performance auto repair shop.  The engine had been removed prior to the expert’s arrival, and was disassembled.

The camshaft bearing surfaces in both cylinder heads exhibited severe wear damage. Severe wear damage was also observed on the mating camshaft bearing caps.   A section at the rear of one of the bearing caps broke off.

The journals on the left and right camshafts exhibited transferred aluminum from the cylinder head bearing surfaces.   Evidence of overheating was also observed at these locations.

The front end of the right camshaft exhibited circumferential scratches, which indicated that the camshaft sprocket had rotated on the camshaft.   Damage was also observed in the slot for the camshaft sprocket alignment key. The corresponding slot in the right camshaft sprocket had been sheared away.

No significant damage was observed on the engine block.   The crankshaft exhibited wear damage on the journal for the number six connecting rod.   The number six connecting rod and its bearing inserts also exhibited excessive wear and heat damage.   A significant amount of aluminum debris was found in the crankshaft oil passages when the engine was disassembled.

The oil pump was partially disassembled for the inspection.   Removal of the oil pump cover revealed that the inner rotor of the gerotor pump was broken.   (Call us if you need the definition of a gerotor pump!)

The damage to the camshafts and camshaft bearing surfaces was caused by insufficient lubrication.   The engine oil level was at its proper level prior to the engine failure, and it was not contaminated.   The owner had specified a premium synthetic oil, which he had received.   So why the lubrication failure?

The answer was found in the viscosity of the oil that was used.   The higher the viscosity number, the thicker the fluid is.   A low number of 5 to 20 indicates a fluid that flows easily at low temperatures-much like water.   A high number like 50 indicates a thicker fluid that flows slowly at low temperatures-much like honey or molasses.   The engine was an overhead cam design, which positions the camshafts on top of the cylinder heads relatively far from the oil pump.   The manufacturer specified a low viscosity 5W-20 motor oil for this engine, in part to ensure that the camshafts received oil from the oil pump shortly after startup.

On both oil changes, the oil change technicians used much higher viscosity motor oil.   The higher viscosity motor oil in the insured’s engine took a longer time to reach the camshaft bearing surfaces.   As a result, the camshafts did not receive adequate lubrication during the first few moments after the engine was started.   Over multiple engine start cycles, this condition caused excessive wear of the camshaft bearing surfaces.

As these surfaces deteriorated, friction between the camshafts and the bearing surfaces increased.   Eventually, the heat created by this friction caused the right camshaft to seize.   As the camshaft suddenly stopped rotating, the timing chain continued to turn the camshaft sprocket.   As a result, the camshaft alignment key slot was sheared out of the sprocket.

The deteriorating camshaft bearing surfaces also caused small pieces of aluminum wear debris to enter the lubrication system.   Some of this debris clogged the oil passages in the crankshaft, which restricted oil flow to the connecting rod bearings and caused the number six connecting rod bearing to fail.   Debris contamination caused the oil pump to fail as well.

Whether through ignorance or carelessness, by refilling the engine with an incorrect, heavier viscosity motor oil, on two separate occasions, the technicians directly contributed to the engine failure

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