M104 oil pressure?
 

Strange oil pressure guage reading on my friends S320. Oil pressure guage behaves as it should when the car is off and you start it. Zeros out, and doesn't rise until the engine starts ect. Seems normal, pegs at 3 bar. The problem is it is always pegged at 3 bar. Once in awhile it migh come down to like 2.75ish a bit, but usualy its always at 3.

What gives? Sensor issue? Car runs fine, Mobil 1 0w40 in the crank with an OE filter. He isn't running 90w gear oil in the thing!:D

I'm used to it resting somewhere between 1 and 2 bar at hot idle, any reason I shouldn't expect this out of a 78k mile M104?

Probably a bad sensor.

the oil pressure gauge in my 94 E320 has shown this ever since I bought it at 80,000 miles, now 3 years later has 134,000; burns no oil and just a little oil seeping at the oil pressure sensor. I thought 3 bar is normal, perhaps I'll change the sensor the next time the Greater Washington Owners Club has a DIY.
Mark

The 104 in the SL idles at about 1.75bar hot. Goes to 3 bar with almost any throttle input.
The 104 in the C280, well, who knows - no gage!

Just went through this with my 95 e320 (104 992 engine) Don't know if this applies to your vehicle

The following from All Data:

Turn key in steering lock to position 2 (battery voltage).
Unplug electrical connection from oil pressure gauge sensor. Specified reading: 3 bar. If specified reading is not achieved: test cable from oil pressure gauge sensor to instrument for short to ground.
Cable in order: replace instrument.
With engine off, oil pressure gauge rises. Connect cable from oil pressure gauge sensor to ground. If reading is 0 bar, replace oil pressure gauge sensor . If reading remains at 3 bar cable has open circuit.

The oil pressure gauge is controlled electrically. The oil pressure gauge sensor installed in the oil filter attachment controls the gauge in the instrument cluster. There will be a positive reading at the oil pressure gauge in the instrument cluster when the ignition is switched on. Negative is applied to the oil pressure gauge through the sensor. As the pressure rises, the ohmic resistance of the oil pressure gauge sensor increases and the reading of the gauge alters.

You have to crawl under the car to get to the oil pressure sending unit. It is located on the lower back of the oil filter housing kind of above the starter. Fastlane parts has a nice picture of what it looks like.

By the way, the wire that connects to the sending unit is not part of the engine wiring harness. I had to replace mine because the insulation was completely decayed.

The oil pressure in my 95 e320 is much higher than my wife's 260E. I have never seen it drop below 2 bar. After a highway drive it drops to 2.25 bar in drive, 2.75 bar in neutral. I assume this is normal for the M104 engine.

What does the temp gauge show after the car has been sufficiently "warmed up"?

Usually hangs just a tick over 80C.

Depends
 

This will depend on what grade of oil you use, temp of car and when your last service was carried out.

Example:

My 104 was just serviced and sticks at 3 bar when cold.

3 bar when not at idle hot.
2 bar when hot at idle.

j m - i know you posted the test for the oil sender gauge and electric wire not being part of the harness in 2006, but wanted to say a huge thanks for this info. going to go over all this today.

since m104 are know to eat head gaskets I run below 80c,with optional thermostat.Oil pressure with some pedal 3 all the time.As low as 1.5 bar at hot idle.