Oil Pressure OM606

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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


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[KarTek]

That's great info, thanks!

[connerm]

Glad you figured it out.