Symptom: oil pressure pegs on startup, but as car warms gets lower and lower. At hot idle it sits at .3 or so. It pegs under acceleration, but under medium driving still fluctuates.

When I got it the oil pressure gauge was really wobbly, and MBI replaced the sender. They say now that the gauge is accurate, but the car just doesn't develop much pressure. Compression is good (380-420 across all 6).

MBI says not to worry about it. That strikes me as odd advice, but in years of dealing with them they've not steered me wrong. It hasn't stopped me from worrying, of course, 'specially given my upcoming plans for a road trip.

I've searched here and read a couple dozen threads, but almost all of them are resolved by replacing the sender. I'm still reading, but meanwhile, please chime in if you have ideas. Thanks!

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2003 E320 wagon, ~80k, "Sputnik"
1987 300 SDL, ~160k, "The Pimp Daddy" (sold April 2010)
1984 300 TD, ~200k, "Das Boot" (Demised March 2008)

Very recent oil change with 15W-40, correct cold reading at dipstick.

__________________
2003 E320 wagon, ~80k, "Sputnik"
1987 300 SDL, ~160k, "The Pimp Daddy" (sold April 2010)
1984 300 TD, ~200k, "Das Boot" (Demised March 2008)

If it pegs the gauge at RPM above idle, shrug, say "The gauge must be flaky", and drive it.

If it ISN'T pegging things at road speed, you've got issues.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

Thanks, Michael. Depends what you mean by "road speed," I guess When hot it pegs at about 2,000 RPM, and has a smooth response until then.

What do you mean by "issues?" (Still reading all the threads here).

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2003 E320 wagon, ~80k, "Sputnik"
1987 300 SDL, ~160k, "The Pimp Daddy" (sold April 2010)
1984 300 TD, ~200k, "Das Boot" (Demised March 2008)

If it were me, I'd ask my mechanic (or do it myself) to screw a mechanical gauge onto the port to see what the actual pressures are.

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1998 E300 +310,000K
1996 E300 +460,000K

Seems like a lot of people, including me, are experiencing this lately.

There was another thread about this here:
http://www.peachparts.com/shopforum/showthread.php?t=219427

My oil pressure pegs at 3 but goes down to zero at idle. This is really starting to scare me and I would like to know what my options are. The way I figure it;
-Put a mechanical pressure gauge on the port and verify pressure.
-Drop oil pan and inspect pump.

The problem is if I drop the oil pan I don't know what to look for. Is there some kind of pressure relief valve?
Has anyone seen worn guides & could that cause the pressure to go so low?

The wierd thing with me is it only does it when the engine is hot. When it's cold it's always at 3 even at idle.

Danny

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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Here is a wild thought. Could your oil temp thermostat be stuck open?? I know that my 86 300sdl has to be driven at least 50-60 miles on the Interstate for the oil thermostat to open and the oil then travel to the oil cooler. When it does that my oil pressure gauge will flicker at idle from 2 down to 1 up to 2 etc. The minute I touch the accelerator it immediately pegs at the needle at 3. On routine 10 mile drives to work it never does this. I attribute this to the oil being sent to the oil cooler which causes the pressure to fluctuate.

Just a thought.

John

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John
1986 300sdl
1985 380se

That's interesting, i didn't think of that. Looking over a parts list on this site there is no mention of a oil thermostat.
Do you have more info on this?
Where it's located? How to test? Where to get a new one?

Thanks

Danny

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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Wow....I can't believe nobody's had problems with low oil pressure before.

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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(='.'=) This is Bunny. Copy and paste bunny into your
(")_(") signature to help him gain world domination

Do the advise of having a mechaincal guage hooked up to get a good reading. Electrical pick up types do have issues with bad senders, loose or dirty connections, etc.

If you pull the pan, you need to inspect the oil pump and its drive chain for excessive wear.

__________________
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

That in itself is perfect behavior for this engine.

If it's un-nervingly low at idle, then definitely a good step would be to get a mechanical gauge in a position where you can monitor it, and see if the gauge is reading accurately at idle as well.

For the sake of quick mental calculuations when you're driving down the road looking at a mechanical psi readout, 15 psi is close enough to 1 bar. So, if the gauge really is reading accurately, then 0.3 bar at idle translates into about 5 psi, which is probably too low.

My suspicion is that the gauge is still not reading accurately due to some cause or another which we'll have to find later. First, get a mechanical gauge and verify the dashboard reading.

__________________


~Michael S.~
Past cars:

1986 300SDL
1987 300SDL
1982 240D
1982 300SD


Current:

1987 300SDL

From what I read in the other thread I linked to earlier an adapter is needed to get a gauge on there. It's a M12x1.5 - NPT. I don't know where to even start looking for one of those.

__________________
1984 300SD Turbo Diesel 150,000 miles

OBK member #23

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(='.'=) This is Bunny. Copy and paste bunny into your
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Here's a place

And here

And here

Bet you could find one locally at a more gearhead-knowledgeable (not AutoZone, Advance, etc.) parts store.

__________________
1998 E300 +310,000K
1996 E300 +460,000K

The issue is a bad oil pressure sender. It is located on the back of the oil filter housing. Unscrew and replace it with a quality VDO new one, your "missing pressure" will now be back. I had the exact same symptoms until I replaced mine. Easy repair. But get the good sender from VDO ($70ish), the others are junk.

__________________
-diesel is not just a fuel, its a way of life-
'15 GLK250 Bluetec 118k - mine - (OC-123,800)
'17 Metris(VITO!) - 37k - wifes (OC-41k)
'09 Sprinter 3500 Winnebago View - 62k (OC - 67k)
'13 ML350 Bluetec - 95k - dad's (OC-98k)
'01 SL500 - 103k(km) - dad's (OC-110,000km)
'16 E400 4matic Sedan - 148k - Brothers (OC-155k)

has anyone replaced this pressure sender on 87 300D ? whats best way to get at it? top or bottom? torque to ? can I use channel locks on the can, I see no way to get wrench on the flats.

__________________
Paul
Benz-less
I need an SDL !