300SD Oil Gauge Flickers at Idle - PeachParts Mercedes-Benz Forum

OtisMagotis · #1 11-24-2015, 01:16 PM

Hi All! New to the forums but have been lurking for awhile. I have been working on a 1981 Mercedes 300SD I bought back in June with my mechanic.

First let me thank everyone in the forums for all of their knowledge, I have been using alot of the discussions to help diagnose some of the issues I have been encountering! So glad this forum exists!

Here is my current issue that I am trying to sort out:

I recently had a valve adjustment done on the car and it made a HUGE difference in the overall engine performance. Very happy with that. I have had some issues with the dashboard gauges since I bought the car (known issue) - Speedometer works, Tachometer does not, Temperature gauge is fine, clock works and the oil Gauge has previously always been buried at the top (3+) unless the car was off.

However after the valve adjustment now the oil gauge is only buried at 3+ when the car is out of idle. As soon as the car goes to idle and even sometimes when I let off the Gas the Oil gauge starts flutter back and forth really fast. If I give the car gas, it then buries itself back at the top. I keep an eye on the oil - measuring weekly or so to make sure there is enough oil, so I am not sure if this is a dash gauge issue, or if the sensor for the Oil level is just bad. Any suggestions?

Some background on the car and where I am at with it. I bought it off a mechanic that was selling it for his customer. The Mechanic had worked on it but honestly was not really a mercedes or diesel guy so there were some mickey-moused issues. Anyway overall the car ran well, with the original transmission and an engine that was replaced from Germany 80K miles ago. Interior was near mint as well - exterior paint job mediocre - but tolerable with no rust. Going through part by part replacing problematic belts, hoses, suspension parts and any over due maintenance issues. This is a long term project for me so I am in it for awhile

mannys9130 · #2 11-25-2015, 06:46 PM

The sender on the oil filter canister is probably bad.

Here's what you can do:

Clean the grounding points behind the cluster, at the engine/trans strap, and at the battery.

Replace the two O rings on the oil filter cap stem.

Replace the sender.

To tell the truth, 15W-40 oil will have the pressure gauge pegged at 3 for a while after starting. Only after a real long full load run would the oil get thin enough to register below 3. In the hot Tucson summer with 15W-40 (before I went to 5W-40 year round) it took me half an hour around town to get down to 2 bar at idle. My 84 has a live gauge, so it's smooth and accurate.

Now, my 85 had an electrical sender. It had 3 places it would stay: 0, 2, 3. At startup, it would tick up to 2 and then 3 on steps. If it was warm and you revved it, it would go from 2 to 3 and back to 2 as if there was no in between. My 84 acts like a real gauge.

JHZR2 · #3 11-25-2015, 08:26 PM

The SD should have a mechanical gauge. Flickering at hot oil temperatures is common - every single w123 Ive owned has done this and all have been healthy and running great.

Mölyapina · #4 11-25-2015, 08:38 PM

Quote:

Originally Posted by JHZR2

The SD should have a mechanical gauge. Flickering at hot oil temperatures is common - every single w123 Ive owned has done this and all have been healthy and running great.

No, it's electric. All the gauges on the W126es are electric.

JHZR2 · #5 11-25-2015, 08:44 PM

My mistake. I was thinking w116.

bricktron · #6 11-25-2015, 11:20 PM

i would clean the sender contact and doublecheck the cluster grounding before replacing any parts.

OtisMagotis · #7 11-26-2015, 01:16 PM

Thanks all, will start with the cluster over the Holiday Weekend. There are some other random issues with the cluster as well (tachometer not working) so hoping it is all related. Will update as I make progress.

bricktron · #8 11-26-2015, 01:39 PM

here is a good guide to adding a supplemental cluster ground on W123. i assume W116/W126 are similar:

http://www.mbelectronicupgrades.com/Cluster%20Ground%20Install%20Guide%20Rev%20A1.pdf

Mxfrank · #9 11-26-2015, 08:58 PM

Just be aware that even new senders fail right out of the box. I took one apart recently:

Photos from inside an oil pressure sender

OtisMagotis · #10 12-10-2015, 03:58 PM

So with the onslaught of the holidays, I have not had a chance to get to this task... The weird thing is that in the mean time - the flickering stopped on its own.

I am wondering now if it is not the cluster but the actual sensor for the oil level and as the oil has gotten dirtier after my last oil change this caused the sensor to stop flickering and probably stop working all together again

toomany MBZ · #11 12-10-2015, 04:48 PM

Beware of problems that fix themselves...

OtisMagotis · #12 12-10-2015, 08:18 PM

Quote:

Originally Posted by toomany MBZ

Beware of problems that fix themselves...

Oh yes always... I have zero faith in the oil gauge at this point and it is becoming a priority to sort out the issue

Clemson88 · #13 12-11-2015, 06:14 AM

The gauge jumped, some of the guys called it 'dodgy.' I replaced the sending unit and it continued.

I soidered the ends of the leads at the sending unit. I'd suggest wiggling the leads while someone observes the gauge to see if that might be the problem. Unsnap the leads from the sending unit and examine them for loose ends.

If that's not the problem then it's most likely the sending unit. I've never read about a gauge failure unless the cluster is faulty.