I too have a 103 motor and became curious about this check valve thing in the oil filter housing.
I just got done reviewing my MB CD-Rom - service task 18-110 - Remove and install oil filter.
If you have access to a 124 or 126 CD-Rom, you might want to take a look at this. The task 18-110 will be for the 103 motor.
There is no check valve shown, but there is an OIL PRESSURE SENSOR and an electrical connection that attaches to the rear of the sensor. Ths sensor seems to connect more to the rear of the oil filter housing.
I purchased my MB used in '97 with 35,000 miles. It now has 96,000 miles and I've experienced no noise whatsoever at start-up; however, I've noticed that it always takes 2-3 secs. before the oil pressure gauge needle rises and this situation only occurs when the engine is stone cold..ie..first start of the day. I use only Mann, Mahle-Knecht; Hengst or on occassion, dealer filters. I live in a warm place and have experimented with both 20W-50 and 10W-40 conventional oil. Same situation, irrespective of oil weight.
After 2-3 secs., the oil pressure rises quickly to 3 BAR and stays there. Once warmed up, the oil pressure rises quickly to 3 bar after the engine rpm is around 1500. I've never experienced problems with fluctuating gauge readings, lifter tick or other noise(s) that would come as the result of faulty oil pressure.
My cam lobes show no signs of galling, nor are there any signs indicative of faulty oil pressure.
I may replace this oil pressure sensor after cleaning the electrical connections simply because I've read here that many 103 owners experience an immediate jump to 3 bar when the engine is started up cold first thing in the morning.
1991 300-SEL - Model 126
M103 - SOHC
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Last edited by Mike Murrell; 01-02-2003 at 01:04 AM.