Update on my car's racka racka
Here's an update on my 92 500E's racka racka at 109K miles:
After I had the oil filter check valve replaced on August 8 (105K miles), the symptoms were greatly reduced, but the engine still occassionally would racka for about half a second upon cold start (well, California cold). Also, there would be occassionally erratic idle oil pressure when warm, that made me speculate that the oil pump pressure relief valve was hanging up. Also the idle oil pressure was dropping to about 1 BAR instead of its usual 1.5BAR, when warm. So I went ahead and had the dealer replace the oil pump pressure relief valve on Nov. 5 (108.8K). While in there, the tech replaced the oil pressure sender unit as well.
Replacing the oil pump pressure relief valve brought NO additional improvement to the frequency or duration of the cold start racka. It still happens occassionally, but still for not more than half a second. The erratic oil pressure has disappeared, however. The oil pressure at idle is still low. I now speculate that this is caused by my switch to Mobil 1 about three changes ago. The dealer uses 0W40 weight Mobil 1 (current Mercedes spec). My older car tends to consume a little and idle at a lower pressure with this lighter-than-original-weight oil. When I top it up with Mobil 1 15W50, it consumes less and idles at 1.5 BAR. Keeping it topped up is the key.
So I'm not sure if I got any real value out of replacing the oil pump pressure relief valve. But with the preventive maintenance I've got peace of mind and pride of ownership, as the current "curator" of this very drivable modern classic!
1995 E320 Wagon Moonstone Grey/Parchment 106K mi.
2007 E63 AMG Graphite/designo 75K mi
Last edited by Mark Stetson; 11-27-2001 at 09:49 PM.