From diesel@wrxtra.com Mon Jul 17 13:52:29 2006 From: J.B. Hebert After many weeks and a few red herrings, we finally tracked down the oil pressure issue plaguing my '95 E300D. Checking through MB's tech bulletins, I thought I had nailed it. On the 606 motors (and probably others) the camshafts are hollow and oil runs down them. There is a freeze plug at either end of the camshaft. According to MB, these freeze plugs can fail and become dislodged. When this happens, all the oil gets pumped up into the valve cover and the low oil light comes on, followed by loss of oil pressure. Since this sounded like my symptoms, we tore down the top of the motor and pulled the valve cover (a time-intensive job on a 606). Sadly, when the camshafts where checked, it was confirmed that all freeze plugs were in place and not leaking. The next step was to check the pan. Instead of dropping the pan, we removed the oil cooler from the side of the pan (which required draining the oil and the coolant, since it is an oil to water heat exchanger). Once removed, the issue quickly became obvious. The screw plug that retains the oil pressure relief valve to the oil pump had backed out to the point where only one or two threads kept it from dropping into the pan. This effectively removed any preload on the oil pressure relief valve spring and put it into "bypass" mode. Since neither the oil pump nor the oil pressure relief valve had ever been replaced or removed on this vehicle, I am at a loss as to how it would have backed out. It was re-torqued to 50 Nm, the vehicle was reassembled, and we manually primed the lubrication system through the pressure sender fitting to make sure all bearings had oil. The engine was restarted and oil pressure immediately returned. Now, I realize that my particular vehicle tends to exhibit problems that by themselves are unusual and rare and in combination almost inconceivably unlikely, but if this happened to me it could happen to someone else. If you happen to have the oil pan off your 606 motor (other 60x might be similar), you might want to re-torque the oil pressure relief valve screw plug while you're in there. If you happen to loose oil pressure, this might be something you want to check. 18-5031HA in the service manual covers the installation and removal of the oil pressure relief valve. Regards, J.B. Hebert ---------------------------------------------- Current Vehicles: '76 Ford Bronco '78 Volvo 262C Bertone V8 '80 Alpina B7 Turbo Coupe '82 Mercedes 300CD (Deceased) '93 GMC Sierra 2500 '95 Mercedes E300D -- No virus found in this outgoing message. Checked by AVG Anti-Virus. Version: 7.1.394 / Virus Database: 268.10.1/389 - Release Date: 7/14/2006