Every w123 I've had fluctuated pressure a bit when fully hot. My 240 seems to be excessive. Runs beautifully and with fine power and pep. Shakes a lot at idle though, perhaps related???

Is this normal? None of my 617 cars shook this much.

OM616 oil pressure fluctuation - YouTube

Thanks!

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

If it is still fluctuating after changing the O-rings at the bottom of the Oil Filter Cap Tube I read somewhere there is an insert that goes inside of the Oil Pressure Line up on the Gauge end to deal with gauge fluctuation.

The above stuff assumes that your Oil Pump, Oil Filter, Oil Pick Up Screen, idle Speed are all working correctly. I think worn Rod Bearings where one is worn more than the other scan also cause Oil Pressure fluctuation.

Gauge going bad?

If the Engine rpm fluctuates the Oil Pressure can fluctuate.

Engine idle rough; Idle Speed too low, Air leak, Injectors?, that Fuel Pressure Relief/Over Flow Valve with a weak spring and Valve Adjustment.

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84 300D, 82 Volvo 244Gl Diesel

My gauge used to do the same thing. I replaced the rubber gasket between the instrument cluster and the dash and it stopped. Accidental fix in this case...

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Did you just pass my 740 at 200 kmh in a 300SD?????

1978 300SD 'Phil' - 1,315,853 Miles And Counting - 1, 317,885 as of 12/27/2012 - 1,333,000 as of 05/10/2013, 1,337,850 as of July 15, 2013, 1,339,000 as of August 13, 2013



100,000 miles since June 2005 Overhaul - Sold January 25th, 2014 After 1,344,246 Miles & 20 Years of Ownership

Rpms don't fluctuate. If I spin the idle up a bit with the knob, idle shake smooths out, but oil pressure increases to the point where it pegs and then it's a non issue. Fully hot, I'd expect like 1.5-2bar at idle when the speed is right - though not scientific, I need to get a tach on it somehow.

At 75k, and given how beautifully the engine runs and drives, low mileage, and full records of great care, I can't imagine anything too dire. The mounts are original, which surely doesnt help.

I don't get how the O rings for bypass in my filter cap would affect it, but I do change them each oil change.

I think an accumulator or a restriction would help. The car is pretty untouched and pristine, which may not help... But it's always done it since I've owned it, a while now...

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

Low compression, if and this is taken with a grain of salt....the engine is low milage its probably carboned up.....a low milage may look nice but performance wise its worse then a high milage example. Change filters and injectors.....do a valve adjustment go for a 6hr freeway trip....re adjust valves, another oil change and do another trip.....probably a lot of gunk in the engine and probably sticking rings....reduced oil flow, due to gunk will cause low pressure....

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If you change them then that is not your issue.
People that have had hard or missing O-rings have had low low idle O-pressure of some fluctuation.

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84 300D, 82 Volvo 244Gl Diesel

The car only ever gets used for 100 mile freeway trips - though low mileage, I NEVER use this around town or low speed/low load applications.

But I've never pulled the gps and done a compression check, so itsa good thing to do after I do a valve adjustment. Thing is, one was done by a dealer within 5k of when I bought the car, and I've only put on a few k myself.

And the pressure is NOT low. Any w123, or any car in general, will not be pegged when at hot idle. That video was hot idle in traffic after like 60 miles on the highway. Cold it pegs at 3 bar, and with the slightest throttle it pegs at 3 bar, just like every single other w123 I've owned. The pressure isn't low, it will drop at hot idle, totally normal, it's the fluctuation, not the pressure that concerns me.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

I had the same problem with my oil gauge, only when the oil was very hot after a long drive:

Fluttering oil gauge on a 1980 Mercedes-Benz 200D - YouTube

It is described in the FSM.



In my case it was solved by installing this pin in the oil pressure line:



But first investigate the basics, as described above.