350SDL Bad Oil Pump? - PeachParts Mercedes-Benz Forum

ezrider · #1 03-08-2004, 02:15 PM

Original owner 350SDL 159K miles. Oil pressure almost nil at idle, just over "2" on gauge at higher RPM. Pressure drop happened suddenly. Engine is still running fine with no abnormal sounds other than lifters due to low oil pressure.

My mechanic recommends oil pump replacement. I hope it's not more serious. Anything else we should be looking at?

Thank you

P.E.Haiges · #2 03-08-2004, 05:10 PM

ezrider,

Seems that something that was done to the engine between the time you had good oil pressure and low oil pressure is the cause of your low oil problem.

Since nothing was done to the oil pump, I doubt if your oil pump is causing the low oil pressure. If the new oil pump doesn't solve the problem, will you mechanic not charge you for it or at least not charge you for the R&R labor? Seems only fair that he does.

P E H

ezrider · #3 03-08-2004, 06:07 PM

P.E.Haiges,

The bad pump is the mechanic's diagnosis, he admits that may not be the problem but wants to start with the pump. What else would you suggest as a source of the problem that could be found and fixed before a pump replacement.

Thank you.

P.E.Haiges · #4 03-08-2004, 06:36 PM

EZ,

I have been thinking about this and can't think of anything during an oil change that would affect oil pressure except the oil filter. I am just saying from experience that when something doesn't work right all of a sudden, look at the last thing that was done and quite often that finds the problem.

Have you analyzed the oil to make sure it isn't antifreeze or some other low viscosity fluid?

Two things that could cause low oil pressure other than the oil pump, would be a blockage or a leak internal to the engine. In the oil filter there is a bypass section in the filter that returns the oil to the sump. If somehow the bypass filter is leaking oil thru or past it, this could reduce the oil pressure. A blockage could be caused by the full flow section of the oil filter having a restriction. I would make sure the filter is the correct one and installed correctly before replacing the oil pump.

Is the car at the shop that did the oil change? If so, they won't want to admit they did anything wrong, so you will have to watch them work. Have them document any mistake they made because the engine could fail from being run with oil in the future. If at a different mechanic, have him document anything he does to fix the problem.

Good Luck

P E H

whunter · #5 03-08-2004, 06:54 PM

remove doubt.
Have the mechanic you trust, do a proper oil and filter change.
Then go on to diagnostics if needed.

ezrider · #6 03-08-2004, 07:11 PM

The oil that the MB dealer put in still looks and feels right to the touch and the filter is the correct one. The car went about 350 miles after the oil change before the problem developed. I agree with my mechanic that there is little possibility that the dealer would admit to any wrong doing or mistakes and we can't find any mistakes yet except for them not replacing the hardened "O" rings on the oil filter stem.

engatwork · #7 03-08-2004, 08:27 PM

Long shot but make sure the connector is tight/clean at the oil pressure sending unit.

P.E.Haiges · #8 03-08-2004, 09:37 PM

EZ,

Did you check the oil pressure with another gage someplace else other than where the oil line to the gage is attached?

If the second oil gage shows low oil pressure it looks like your last chance is to replace the oil pump. I hope you can get at it thru the lower oil pan. I never removed a chain driven oil pump so I'm no help there. I know the shaft driven oil pumps were R&R with only the lower oil pan off.

P E H

ezrider · #9 03-08-2004, 09:44 PM

engatwork,

The lifters get noisy right after it starts up and little oil is visible when looking in the valve cover with the oil filler cap is off.

Eric Eliel · #10 03-08-2004, 11:46 PM

I know nothing about a 350SDL, however I found the round rubber filter seal (from the bottom of the filter) in the bottom of the oil filter housing. It was partially blocking part of the oil path. If you push these filters on incorrectly or the rubber seal isn't lubricated prior to installation, the bottom seal can come off. This was on a 617 engine.

I don't know if the same thing can happen on a 350SDL.

P.E.Haiges · #11 03-08-2004, 11:55 PM

EZ,

I didn't realize you had 300+ miles between the oil change and when the low oil pressuer problem started. If there was no oil pressure at all I could understand a broken pump or pump chain.

I had a 190D that broke the shaft to the oil pump. Drove it too far and ruined the engine. It ran OK but would only start with a roll or push start. Some how fried the rings. I had to replace the rings and bearings.

P E H

CSchmidt · #12 03-11-2004, 09:57 PM

Folks,

I changed my oil 1000 miles and 6 weeks ago on my 603 engine.
When I changed the oil I replaced 1 of the 2 o-rings on the filter cover shaft that goes down throught the filter ( the dealer only had 1). M1 15-50 oil and a Hengst (sp?) filter. All is acting as usual...

So I hurt my back and have been horizontal for most of the last month. I start driving again (after reading some of these posts). My usual pressure is 1.5+ at idle and 3 for anything above idle. Yesterday I had the same symptoms as this thread. Under 1 bar at idle and still below 3 at 2k+ rpms. WTF!

I hit the dealer again today and got more o-rings. I replaced the 1 remaining old o-ring and reseated the filter and cover. The remaining o-ring (upper one) was so brittle it broke instead of streching off. The pressure is back to typical, at least tonight. I'll let you know if that holds tomorrow.

Chuck

ezrider · #13 03-15-2004, 03:25 PM

I just got what I hope is very good news from the local MB dealer shop that dropped my oil pan to investigate my low oil pressure problem.

They told me that the windage tray in the oil pan came loose from it's mounting bolts and caused the oil pump pick up to become obstructed, the tray or something else also some how caused the piston oilers to become damaged and they need to be replaced.

They say there does not appear to be any damage beyond what they see and the bearings seem OK. They are going to replace the oil pump as a precaution and piston oilers and expect the motor to be OK after this.

Needless to say, I will be extremly happy if this works out as it looks like it may.

P.E.Haiges · #14 03-15-2004, 06:34 PM

EZ,

I'm glad to hear it wasn't anything serious.

P E H

ezrider · #15 03-15-2004, 07:00 PM

Thanks,

PEH, I have my fingers and toes crossed.

I'm going to start doing my own oil changes using a Topsider or something similar. I found a MB service bulletin from MB on ALLDATA that says suction oil changes from the dipstick tube is an acceptable method on the 350 SDL. I'm seriously considering switching to 15-50 Mobil 1 with frequent filter changes the first 3,000 miles. My mechanic says I'm looking for trouble by knocking sludge loose with Mobil 1. I know this topic has been discussed ad nauseum on other oil threads but how throughroly has it been discussed regarding 350SDL's?

Thank you.