Hey so I've been driving my 85 300D for awhile now and I could have sworn the oil pressure gauge is supposed to fluctuate when slowing down and accelerating.

My gauge shoots up to 3 when I start the car and stays there until I turn the car off. This doesn't seem right to me

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-Typos courtesy of my mobile phone.

Part of the problem with the MB gauges is that they do not indicate actual oil pressure above 3 bar. They cannot depict fluctuations that are "off the scale." However, with the engine at operating temp,idle rpm pressure is typically in the 1.2-2.0 bar range.

At idle, when hot, most Mercedes diesels drop to 1-2 bar depending on the age of and wear on the engine. The factory says anything above about 0.5 bar is OK at idle so long as the pressure goes up at engine speeds above idle. It also depends on the viscosity of the oil you use. Since your engine has a mechanical oil pressure gauge, it would be advisable to install a substitute gauge. Perhaps the Bourdon tube in your gauge has weakened with age (is this possible? I don't know) and is really reading in error. If your engine really has 300,000 miles on it then you will want to know the oil pressure accurately.

Jeremy

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"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

If it shoots up with just the key on but not running, then the sender is bad or disconnected.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

Does an '85 300D have a sender?

IIRC, the w123 used mechanical oil guages, even in '85.

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

91 W124 300D Turbo replaced, Pressure W/G actuator installed. 210K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Possible. I thought that all 85's were electrical.

I guess not.

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Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

It is a mechanical gauge. I own one. SDs (W126) had electric oil pressure gauges, W123s all had mechanical gauges.

__________________

"Buster" in the '95

Our all-Diesel family
1996 E300D (W210) . .338,000 miles Wife's car
2005 E320 CDI . . 113,000 miles My car
Santa Rosa population 176,762 (2022)
Total. . . . . . . . . . . . 627,762
"Oh lord won't you buy me a Mercedes Benz."
-- Janis Joplin, October 1, 1970

That's odd. Same engine.

I guess they kept the old cluster in the 123.

__________________
Michael LaFleur

'05 E320 CDI - 86,000 miles
'86 300SDL - 360,000 miles
'85 300SD - 150,000 miles (sold)
'89 190D - 120,000 miles (sold)
'85 300SD - 317,000 miles (sold)
'98 ML320 - 270,000 miles (sold)
'75 300D - 170,000 miles (sold)
'83 Harley Davidson FLTC (Broken again) :-(
'61 Plymouth Valiant - 60k mikes
2004 Papillon (Oliver)
2005 Tzitzu (Griffon)
2009 Welsh Corgi (Buba)

My gauge does the same thing. Takes about 1sec after engine startup to hit 3bar, then stays there until I kill the engine.

One day maybe I will hunt down a replacement, but I have other things on my list to do first.

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Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Not the same engine. If they were the same, they wouldn't be different!!!

Yeah it's a mechanical pressure gauge.

The gauge shoots up to 3 when I immediately turn the engine on.

I'm guessing this has gone bad. I wonder if there's anyway to fix it.

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-Typos courtesy of my mobile phone.