Originally Posted by dpkreuze

Comrades,
My close friend replaced the engine oil cooler on a 137.970 v12 in a 2002 CL600 produced on 07/30/01. This repair involves R&R of both cylinder heads. Since then the engine makes a knocking noise eminating fron the upper left rear area of the engine. This sound is like a lifter noise. However to me it sounds more like the old engine mounted Pierburg vacuum pumps when they went bad. Thud, thud, thud, in sync with the engine speed. He tells me that the sound is not audible until the engine warms up. He changed the engine oil and tried to flush the engine crankcase with additives to the engine oil. What think Ye?
Peace,
Don