1986 300sdl newbie again...

So I'm curious:

On start up, the oil pressure fires up to "3", sits there for a while, and them moseys down to 2.5. While the engine is still relatively cool, it works. Then, once I get going, after a while of driving, it just drops to zero. The engine still runs. In face I was full throttle on the highway recently, and it doesn't "appear" to affect the engine, but it's weirding me out anyhow.

I suspect its a sensor issue or a blown fuse(?), something of that sort -- this is what i suspect. Obviously, if there was no oil pressure, the engine would seize up and die, and since it doesn't run on fairy dust, this is my best guess.

I would appreciate any advice.

I've attached a picture

Attached Thumbnails

 

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Ethan Hunter
1986 Mercedes-Benz 300SDL (263,000 miles)

My guess would be, you have a faulty oil sending unit. on your engine it would be electric, and probably mounted on the oil filter housing.


Charlie

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there were three HP ratings on the OM616...

1) Not much power
2) Even less power
3) Not nearly enough power!! 240D w/auto

Anyone that thinks a 240D is slow drives too fast.

80 240D Naturally Exasperated, 4-Spd 388k DD 150mph spedo 3:58 Diff

We are advised to NOT judge ALL Muslims by the actions of a few lunatics, but we are encouraged to judge ALL gun owners by the actions of a few lunatics. Funny how that works

I have the same issue, so I took it to my local Mercedes specialist, they told me the oil sending unit needed replacing, so I went for it, the day I picked it up I will still having the same problem so either they put in a faulty oil sending unit (unlikely) or there's another issue (hopefully minor!).
If anyone has any advice or can help it would be greatly appreciated!!

Thank you,

B

To test your sender (with engine off, but vehicle turned on), unplug the wire to the oil pressure sender and the indicated pressure should peg at 3. Ground the wire to the oil pressure sender, and the indicated pressure should be zero.

If you are getting zero indicated pressure, but still have oil flow when the engine is on, perhaps you have an intermittent ground in the wire. Maybe once your car warms up, the wire is grounded, but when the car is cold, the wire for whatever reason is working fine. Good luck.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

Please excuse my ignorance as this is both my first diesel and first Mercedes but can you tell where this wire is? So simply unplugging it will give me a reading of 3? And plugging it back in will give me 0? And if this is the case what will this show me? That my oil sending unit is bad or good?
Again thank you for your help!!

So would this tell me if my oil sending unit is good or bad?
Thanks again,
B

I would start with changing the sensor. It is a little silver can on the base of the oil filter tower. Right above the starter. So make sure to disconnect the battery before going in there since the big + cable is right there where you are working.

I just did it a couple weeks ago. I have the same engine as you in my 300TD.

87 300TD OM603.960 Oil Pressure Sensor Replacement

Pulling the IM will be the worst part. You will need a long 6 mm hex driver and a lot of patience.

When you order up the sensor also order the IM gasket and the crossover pipe gasket since you will probably need to replace them as well.

It is not necessary to drain the oil to change the sensor, I lost maybe a teaspoon.

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The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Is this sensor different than the oil sending unit I just had replaced yesterday? Cuz I thought getting that replaced would've fixed the issue...

Nope, sorry, I didn't see where you said you replaced it. They are one in the same.

I am now thinking bad wire or bad gauge.

But wait, check your fuses and make sure it's not a flakey fuse connection.

__________________
The OM 642/722.9 powered family
Still going strong
2014 ML350 Bluetec (wife's DD)
2013 E350 Bluetec (my DD)

both my kids cars went to junkyard in 2023
2008 ML320 CDI (Older son’s DD) fatal transmission failure, water soaked/fried rear SAM, numerous other issues, just too far gone to save (165k miles)
2008 E320 Bluetec (Younger son's DD) injector failed open and diluted oil with diesel, spun main bearings (240k miles)

1998 E300DT sold to TimFreeh
1987 300TD sold to vstech

Not relevant here because the sender has been replaced, but for future readers, you do not need to remove the intake manifold to replace the oil pressure sender on an OM603. See post 10 of this thread for an easier way:
Oil pressure anomolies... hope I didn't just destroy my car

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).