My E320's oil pressure suddenly dropped to .3-.5 bar at idle yesterday, with no perceived change in engine behavior. Changed the oil (15w40 diesel oil) and filter, added some MMO on the theory that gas in the oil had possibly gummed up the bypass valve--engine is also running rich due to EGR malfunction and possible vac leak. Pressure comes right up with revs, 3 bar by 1800RPM.
Took it out for an ITU after oil change (pressure at idle was 3 bar beforehand), ran great, but is now making a chirping/squeaking noise from the top end...sounds like maybe oil starvation to the valve train. Noise tracks with engine RPM and doesn't seem to go away with revs. Opened oil cap while running, splashes oil but much less than I remember my last M104 doing.
Oil pressure now about .5-.7 bar at idle, still comes right up with revs as expected.

Video of noise: https://youtu.be/M5vs_U4uO10

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

May be two unrelated problems...bad bottom end/oil pressure on a 104 is not very likely...here is my long distance diagnosis:

1. Low oil pressure reading due to a faulty sending unit, and

2. Chirping/squealing loose belt due to failing belt tensioner.

Mist water on the belt to see if it changes the chirping.

Good luck and keep us posted!!!

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"Rudeness is a weak man's imitation of strength" - Eric Hoffer

Sudden oil pressure issues are probably the sender as mentioned above. Mine failed suddenly and without warning, reading 0 at idle and ~1 at 3000 RPM. A replacement sender fixed the issue.

If there's oil splashing around under the valve cover at idle, it's highly unlikely that the noise you're hearing is the camshaft squealing. Check for belt issues or a tensioner pulley failing.

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

ADDITIONAL DATA: noise only happens when engine is fully warmed up, is coming from the front of the engine, cannot be heard with stethoscope on valve or timing cover, and is at serp belt frequency. As such, I believe the squeal to be the fan pulley bracket bearing, and the oil pressure issue to be a bad sender—zero indication of rough running or vibration with nearly zero pressure indicated.

Appreciate the help, y'all!

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

I had to replace my idler pulley,and also the oil sender.I used teflon paste on the threads.Learned to use it instead of tape when I ran nitrous.

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1999 w140, quit voting to old, and to old to fight, a god damned veteran

Diesels (I know this car isn't a diesel) make such an array of noise that it makes it really hard to pinpoint where an odd one is coming from. My SDL was making an intermittent "squeak" noise that you'd swear was a wrist pin, only when hot, and only for a brief period. Tracking that one down was a pain, but I was in the same boat as you - engine ran fine, no other noises, oil splashing around everywhere. Turned out to be the water pump. That's another story in itself playing out in another thread in the diesel section...

__________________
Current stable:
1995 E320 149K (Nancy)
1983 500SL 120K (SLoL)

Black Sheep:
1985 524TD 167K (TotalDumpster™)

Gone but not forgotten:
1986 300SDL (RIP)
1991 350SD
1991 560SEL
1990 560SEL
1986 500SEL Euro (Rusted to nothing at 47K!)

Boy I know that problem. Anytime my OM617 makes a new noise I check to see if it sounds like a vacuum pump or timing chain, and if it's not I just ignore it.

Water pump is my second guess, but it really sounds like it's further towards the right side of the engine. New bracket is on it's way, so I'll just have to wait and see!

__________________
RIP:
2011 E350 BlueTEC, Schwartz 81k (totaled by uninsured drunk driver)
1964 Unimog 404.1 (wrongfully towed by the city)
1994 E320, Brilliantsilber 208k (transmission shuffled off after sudden catastrophic fluid loss)
1982 300D, Silberblau under a blue repaint 256k (sold for parts)
1995 E320 Polarweiss, 131k (sold for parts)
1995 E300D Polarweiss, 287k (totaled by drunk driver)

My guess is that the MMO, which is very thin, has diluted the 15w40, causing the oil to be thinner than you are used to. Thin oil tends to give lower hot idle oil pressure because thin oil leaks out of the bearings faster than thicker oil. The pressures you mention do not seem to me to be problematic.

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'97 E 300 D

okto, if you use a high quality oil there is no need for any "magic potions" because there are detergents in oils to keep the engine internals clean and the oil flowing freely. It is important to change oil and the oil filter on a regular basis, with the oil hot. For your 1994 E320 every 7,500 miles should be fine.

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Fred Hoelzle