Oil Change Causes Oil Pressure Problems? - PeachParts Mercedes-Benz Forum

ezrider · #1 03-08-2004, 10:41 AM

I am the original owner of a 1991 350 SDL with 159K miles on it now. I had my oil changed recently at my local MB dealer as I have done many times in the past. The engine has no history of oil pressure, or any other significant problems.

When I picked up the car after the oil change I noticed the oil pressure gauge twitching a little bit at idle, I have never noticed this before. Yesterday after 350 miles the pressure dropped to near zero at idle and "2+" on the gauge at 2300 RPM and above. It was always pegged at "3" at anything much more than idle in the past. I believe the gauge because I can hear some lifter noise at idle that has never been there before.

Today I had a ex-MB mechanic, now independent, evaluate the problem. He found the "O" rings on the oil filter stem rock hard and said they should be changed with each filter change. He changed the "O" rings but we did not get an improvement. He says the oil pump could have failed due to starvation caused by the old "O" rings. He said my hard "O" rings could be the root of my problem. He confirmed that my oil pressure is a problem and is hoping a new oil pump will solve it, but that it could be worse.

He also suggested that I talk to the MB dealer that should have changed the "O" rings and didn't.

Has anyone here experienced oil pressure failure due to these "O" rings?

I would appreciate any advice on how I should approach the dealer.

Thank you.

psfred · #2 03-08-2004, 11:41 AM

No, usually those o-rings just cause the lifters to rattle, not the main bearing oil pressure to drop.

The oil pump won't get straved by a loss of pressure, it draws right off the sump. I'd be more worried about the main bearings being damaged from oil starvation. A new oil pump will only fix the problem if the pump is bad -- note that at least one other poster HAS had a 603 oil pump fail.

Did you change the filter to a known correct one? I don't know what the filter housing is like on the 603, but on the 617 incorrect installation can dislodge a seal on the filter and cause low oil pressure.

Peter

psychoman · #3 03-10-2004, 09:59 AM

I had the same problem with my 380SE in close inspection of the oil sending unit, it was leaking by the transducer or what ever it uses to send the signal. RR it cahnged oil and had great oil pressure again. Not sure if 350SDL is mechanical though like SD.
Good luck.

rosshudson · #4 12-18-2005, 04:22 PM

I am having the same problems currently after a trubo replacement on my wifes 1991 350sdl. It started after a trubo replacement and an oil change. It would not build oil pressure at all. Replaced the orings and now the pressure is low and dropps to o when accelerating. Once you are at speed it comes up to 1.5-2 ...some times up to 3 like it used too. What was the fix for your car? . where is the oil pressure sending unit? I hooked a manuel gauge to what apperared to be a sending unit on the bottom of the oil filter housing. It read 15 psi at idle and up to 80 at speed. but the dash gauge also read , so this was not the sending unit for the oil pressure gauge.
Does anyone have any ideas, any help or similar problem on another model.
Thanks

alanintn · #5 12-18-2005, 04:53 PM

I would say that that is the sending unit for the oil preassure. It is the sending unit for my 380SE. And it did fix my gauge. I mine was leaking by the sending uint and causing it to drip. If you have 80 psi there you do have oil preassure. When I changed mine it brought it back to full scale. The unit meassure for bar is 1 bar = about 14.6 psi I think so full scle on 3 is over 60psi. Someone can chime in on this to veryfy. Alan