1995 E-320 Oil Pressure concerns

speedt1 · Oct 12, 2009

I have a Real nice E320 wagon that is not a daily driver but a couple of days a week car. Earlier this summer I noticed the oil pressure dropping to near 0 at idle. When the engine rpm's are brought back up the oil pressure will go right back up also. It holds pretty steady at driving speed but certainly not like normal. The oil had been changed within a few thousand miles so I decided to change it and the filter again first. This did not change the condition, I also ordered a new pressure sender but have not figured how in the heck they are installed back there against the firewall.. Any other possibilities?, I opened the oil filler cap and you can see oil in circulation at the rocker arms but that guage resting around 0 makes me very nervous and have essentially parked the car for the last few months..
Any help would be greatly appreciated....

loubapache · Oct 12, 2009

I am moving this to W124 forum.

mckellyb · Oct 12, 2009

EEK!

Is does it register at idle when first started... i.e. when the engine is cold?

Did it ever read normally? If so, when it failed to register, did it just stop doing so one day, or was it gradually less and less pressure indicated?

speedt1 · Oct 12, 2009

When first started the oil pressure is perfect..then as the engine warms up the presure slowly starts dropping to the lower levels and then will rest around 0 when at idle. When the engine is then accelerated the oil pressure quickly jumps up but then will drop back down with rpm's..
The car was perfect then I drove it home for lunch one day and noticed the pressure when I turned the car off. This is after not driving the car for a couple of weeks so I not sure what the heck was going on, but thought that was not what I remembered seeing.
Seems I remember the oil pressure gauge not changing very much from first starting to other driving conditions on the car before. Not really going from zero to 3 unless the car was running(of course) and then not changing very much after that until the car was turned off..If that makes any sense...

neanderthal · Oct 12, 2009

That can happen if you use a thinner oil or a thinner synthetic oil. What oil are you using?

speedt1 · Oct 12, 2009

30 weight standard oil

mckellyb · Oct 12, 2009

Hmph.

Well. It sounds like the sending unit is okay...which is bad, because it should register oil pressure at idle.

You're not getting lifter clatter at idle when the engine is at operating temp, are you?

speedt1 · Oct 12, 2009

No, the motor purrs like it should and I actually do not notice anything unusual. If that gauge was not fluctuating around like it is I would not be concerned with anything on the car.

latief · Oct 13, 2009

When i did my headgasket on my 1993, i found that the small wiring harness going to the oil sending unit was environmentally friendly

, it is the biodegradable type wire and was causing my oil pressure sender to act all weird. lookup my headgasket thread and see the picture of it. that might be what is causing this + a new sender unit.......

good luck

mckellyb · Oct 13, 2009

If all sounds well, then yeah, I can see it being the wiring.

Mercedes, of all manufacturers, should not have used wiring insulation which intentionally degraded over less than say, a century.

speedt1 · Oct 13, 2009

Thanks for all the input and that Headgasket thread is quite informative....I do not remember what I paid to have mine done a few years ago but it was money WELL spent after reading that... I will look at the wiring tomorrow and report back anything that I find..... I am also going to look inside the oil filler cap and see if I tell the difference in oil flow when the engine is cold and showing good pressure and when then it warms up and starts to show the erratic presssure...
Thanks Again......

J. M. van Swaay · Oct 13, 2009

I had the exact same symptoms on one of my cars, turned out to be a defective sending unit. Fairly common problem on the 94/95 E320. Sending unit is kinda behind the oil filter housing, it is accessible from underneath the car, drivers side. Space is limited, helps to have a stubby wrench. Takes about 15 minutes to change if you've done one before, otherwise figure an hour. (I say an hour because it will take you 45 minutes to figure out how to get a wrench on it.............)

J. M. van Swaay

Aero I · Oct 13, 2009

Ditto here, same as Van Swaay

J. M. van Swaay said:
I had the exact same symptoms on one of my cars, turned out to be a defective sending unit. Fairly common problem on the 94/95 E320.

J. M. van Swaay

Exact same symptom also, and when I called my indy he wasn't concerned at all, said wait until next service and he would change out the sending unit.

I waited, took it in eventually and he was right. Same motor, same oil, same filter type, now idles around 2 after warm-up, back up to 3 when rpms's go over idle...

Indy said very common to all 104 motors no matter what size they are. He says if taken care of, the bottom ends never go bad and 99 times out of 100 low oil pressure is a bad sender.

But I will say that it feels much better looking at a working gauge with great oil pressure. Even though he assured me, I was never really comfortable until it got fixed.

Good Luck

neanderthal · Oct 13, 2009

Being that the oil pressure is the most important metric being measured by the engine's sensors I would say that you should take any oil issues seriously, even when you suspect its nothing but an electrical problem.
Once you have established that it is indeed the oil pressure sender, then perhaps you can relax a little bit.

speedt1 · Oct 13, 2009

Well, I will report that I did the visual check on the flow of oil at the filler cap and when cold and after driving around the block and warming up the motor the flow/pressure seems to be the same. I can manually rev up the motor and oil shoots right out of the hole and there appears to be NO difference in the amount of oil flowing on the cams. It is just strange to have it only happen when the engine warms up, I would understand and be a bit more comfortable if it was completley erratic and was messing up when the engine was both warm and cold....
I have the sensor in hand I will climb under this beast and see (or try to see) to get this changed out....

Thanks again, this forum is the best.....

Muzungu · Oct 14, 2009

My car was the same way, first start when cold, pressure gauge would shoot to 3 bar. Had to drive it on the highway for 15 to 20 miles then the oil pressure gauge would read "0" at idle in gear.

Replace the sender and I'll bet everything will be fine.
If you have big hands and arms it might be easier to remove the air cleaner housing to access the sender (if the '95 wagon is similar to mine).
Be sure to get the old washer/gasket off of the oil filter housing as it is hard to see. I used a dab of grease to hold the new washer on the sender while installing it.
Also, it seems like it takes a few days of driving to get all of the air out of the new sender because at first on hot idle the new sender would only read about 0.8 bar and now it reads 1.3 bar in gear at hot idle.

Good luck, and I fully understand how uncomfortable it is to see the gauge read 0 even though everything "checks out"!

Cheers

And I agree........this forum IS the best!

orange911 · Oct 15, 2009

I changed the sensor in mine earlier this year because it read 0 while running

After the change the pressure reads slightly higher than 0 when off. So my calibration on the new sending unit is out of wack. I didn't want to bother removing and returning... and replacing. So I just know that it is reading about .3 bar high. I have always used Mobile 1 and as long as I see the pressure fluctuate with RPM, I am confident it is good.

ptkacik · Oct 16, 2009

I am a Mechanical Engineering Professor with a motorsports focus and teach Motorsports Instrumentation at UNC Charlotte. I use a W124 oil pressure sender unit as a demo on how pressure senders work because it is sooo mechanical. The pressure pushes up on a metal diaphragm the pushes a lever that moves a wiper across a resistor coil. As it moves, the resistance changes and the Oil Pressure gage reads the voltage and is calibrated in Bar.

Funny thing is that when the diaphragm leaks the pressure reads lower and lower until it reads zero all of the time. I recall replacing mine was not too bad a job but when I cut the old one open, now that was cool (except it was really loaded with oil).

It also only goes to 3 Bar because you don't need to know how much pressure you have above that. Why stress out that it used to be 6 bar and this year it is only 4 bar. Anything over three is just fine so make it peg out at three and it looks good and stable.

If I were you, I'd replace that sender (and maybe even cut the old one up).

Good Luck,
Peter

1995 E-320 Oil Pressure concerns

speedt1

loubapache

mckellyb

speedt1

neanderthal

speedt1

mckellyb

speedt1

latief

mckellyb

speedt1

J. M. van Swaay

Aero I

neanderthal

speedt1

Muzungu

orange911

ptkacik

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