M103 Oil Pump catastrophic failure

My 1986 300SE is now back in business with good oil pressure.   Turns out the reason why the oil pressure was low was a catastrophic failure of the oil pump itself.  In the last part, I had narrowed the problem down to most likely being the pump.   I assumed that something was either blocking the screen or the pressure relief valve was stuck.    At this point it was time to take the car to a professional mechanic to have a look.

On the M103, the engine has to be raised to remove the one piece sump.   Once the sump and oil pump were removed, it was quickly apparent what the problem was.   The screen was fine – intact and no blockages.   The real issue was Oil pump catastrophic failure.

As can be seen in the picture below, there are big chunks out of the pump housing.   These have gone through the impeller gears and chewed them up badly.

M103 Oil Pump Catastrophic Failure

There is a second chunk out of the bottom of the housing too.   My theory is the first chunk broke off and it was debris from this chunk that then cause the second hole in the oil pump.     Along the way the impeller gears were badly scored and if you rub your finger on the housing you can feel where it was damaged too.


While the sump was removed, it was carefully checked for any debris.  None was found.   I never saw any when I changed the oil, or when I took off the valve cover.   My assumption that the oil filter caught it.   I can no longer cut open that filter to check though.   In my opinion the cartridge style filters are much better than spin-on.  I always inspect the filter itself when removing it.   This is not easily done with the spin-on filter.

The pump was replaced with a new Febi unit.   I wouldn’t have normally used a Febi for something like this, but I remember on a video from the MMWA youtube channel that the M104 Febi pump is made in Germany.   This proved right as the new pump arrived marked as made in West Germany.



The new pump is now installed and the car is running well.  I’ve done a few hundred kilometers on the car and I have not noticed any issues.    The failure of the original pump is interesting.   My mechanic, who is very experienced in these cars had not seen a failure like that before.   I had also not found anyone on forums mentioning such a failure either.    I made a video (below) to better show the failed oil pump.   You can see the carnage in more graphic detail than you can with the photos above.

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