Joseph_H

Question 1:
Does anyone know what might cause an oil pressure gauge on my '95 E420 to drop momentarily to 0 while driving during cold outside temp then goes back up to 3. I checked the oil level and was fine and was changed recently. I am suspecting the oil pressure sending unit. any ideas? This only happened once while it was cold outside. No malfunction light came on.

Question2:
Is it easy to replace the oil pressure sending unit?

Question 3:
If anyone has specific instructions on how to change the oil pressure sending unit on a 95 w 124.034 (E420) would appreciate an e-mail or something.
joseph_hussein@hotmail.com

bamberger_1

Before you go for that replacing the pressure sending unit, and the oil gauge going to 0 only happend once, just pull the intrument cluster and check all the connectors, may be they just came "loose" and need to be plugged tightly again.
When you pulled the cluster measure the resistance of the sensor. It is contact No 4 on the 4-prong connector. Maeasure against ground:
no pressure 10 Ohm, 1 bar 69 Ohm, 2 bar 129 Ohm, and 3 bar 184 Ohm.
I think its not a severe problem, at least I hope for you. (The sensor sits close to the oil filter).

Joseph_H

To pull the instrument cluster?
It seems that everyone talks about pulling the instrument cluster as if it were as easy as opening the hood! I don't mean to be sarcastic but really serious. I have a feeling that if i was to pull the instrument cluster I would never be able to put it back the way it was.. then i have nightmares with hearing squeaks and loose stuff i may create by pulling off the cluster. I guess i see how tight and neat the instrument cluster is fixed i can't even imaging taking it apart.... I also will have no clue where to start to pull...
In any case, i took a look at the oil pressure sending unit and found some oil leaking around that area. I couldn't tell if the oil; was leaking from the sensor itself or not. I also found that the wire to the sensor is very brittle and cracked from heat. So i decided to replace the sensor and fix the wire. I also noticed that the oil pan had some minor leaks around the gasket so will replace the gasket there all at the same time. I hope it was all just a sign for me to replace this stuff and see how it goes. I still think doing all that is a lot easier than pulling the instrument cluster! I will have to find a way to learn how to take the cluster off since sooner or later I will have to do it if I ever needed to do so then it may not be all that bad... thanks for the feedback bamberger.

bamberger_1

Hi,
the leaks you see around the sensor come most probably from the filter changes. When the filter is change a minor amount of oil leaks out and settles down in that area. The oil pan leaks arn't worth fixing, unless it's really bigger amount of oil which need to be replaced withi short times. e.g. 1 quart per 1000mls or so. In most cases the oil comes from somewhere else and is driven by the airstream somewhere on the lower parts of the engine. It could come from the front covers of the block, the head gasket, the valve cover ....
Pulling the cluster is not "dangerous" but elaborate. You need to take the steering wheel off, loosen the flex shaft of the odometer in the foot room behind the carpet, build yourself two little hooks which go behind the frame of the cluster for each side and pull as far as it goes. Then turn it a little bid to the side to unscrew the flex shaft at the back of the cluster, and here you are. Unplug the wires, vacuumhose and the rest of it. The harder part is putting the cluster back since you need to put back the odometer flex shaft w/o seeing anything.
Hope your cure changing the sensor and the wires will work for you.

Joseph_H

... the oil pressure needle dropped to "0" yesterday and stayed there. i decided to leave the car alone until i get the sensor and then go to work on it this weekend. I will test the oil sensor (sending unit) first to make sure it is the culprit. From reading and researching i came up with the following test criteria:
-disconnect wire connector from sensor and ground it, the gauge should read 3 bar, if not replace the sensor

I hope I got it right. If the problem with the wire or gauge then that will be another deal to work with.

I think you are correct about oil leak being part of the oil change from the filter housing because the oil leak looks somewhat clean!. I will have an update and maybe some pictures once I am done with this task.

bamberger_1

I hope it's nothing really serious, like bad crankshaft bearings, with let the oil pressure drop also. Do you hear any abnormal noises for the engine??

To check the sensor I have looked into some tech-books. They recommend the following:
*switch on ignition, dont start the engine, pull the plug of the sensor, and you should see 3 bar
* connect the cable to ground and the gauge shall slowly move to 0 bar.
In light of this it seems your sensor resp. cable may have permanent or occassional contact to ground.
Good luck