Why is there oil under my dash?!?!?
 

My 240D has been getting oil on my shoes, so I took the under-dash panels off. Sure enough, there is oil in there!

How is that black engine oil getting in there under the dash? Almost all the oil is on that black panel that fills the space between the tan under dash panel and the fire wall.
Here's a photo of the panel.
Attachment 169405

One of two items...the hose to the oil pressure gauge is leaking and/or the oil pressure gauge is leaking.

OH! I've noticed that the oil pressure has started dropping to about 2 at idle. I bet that's why for both. Wonder what parts are available.

A W123 instrument cluster shouldn't be overly difficult to find.

Last resort, or for the temporary fix, you could cap the gauge line supply off at the oil filter.


A better option (if a good gauge and line can't be found), just get an aftermarket gauge, whether it be electronic or mechanical.

The oil gauge is prone to leak after 30-40 years of service. Common failure mode. The gauge expands and contracts to move the needle, the solder joint gave way. You would not notice any changes in reading unless oil is literally gushing out. You can replace the gauge, not easy, as room is right. I removed the gauge, thoroughly cleaned and JB weld it. I checked for leak by screwing it back in and run the car without the dash. Car will start and run but you loose all turn signals and everything electrical. Good luck.

He needs to determine if it is the gauge or the line.

After years and years of flexing bourdon tubes in gauges get metal fatigue, crystalize and start cracking.

AK - That’s cool that you could JB weld it. I’ve wondered how to fix them over the years. Luckily I have the electrics in my *current diesels but my old 240 did leak for the prior owner. I found signs under the mats. I was wiping up oil for years under the floor mats.

There was a thread here many years ago about soldering the bourdon tube where it fatigues. I don’t recall if it was soft soldered or silver soldered. Torch or electric iron. It sounded like a path forward if we cannot find gauges anymore.

*wait a second…I think I’m getting my 300SD mixed up with my 300d. My 300D has the little black oil tube behind the dash. I think it’s the SD that has the electrical sender. I’ll have to keep a repair in mind in the near future. The car is getting to the age where the gauge leaks.

ETA - here is some old info from the forum. You guys are amazing.

https://www.peachparts.com/shopforum/3266831-post25.html

Remove the dash, remove the gauge ( a lot of work ), clean the oil gauge and screw it back in. Start the car with only the oil gauge in place then you can tell within seconds where is the oil leak, the line or the gauge ( note the solder joint on the curve tube ). It is very unlikely to be the line.

Once you spot where the oil is coming from, clean the surface with brake cleaner, roughen the surface and JB weld it. Retest after dry. Done.

BTW: I have also tried to resolder it with a blow touch. Need to protect the spring with a heat shield as the heat might destroy the circular spring. I think JB weld is the best. The hairline crack can be sealed easily by the weld.

Good to know. I took a look at eBay for replacement gauges. People want a lot of money for old gauges.

I read some old threads here. Like ones where you wanted to put an electronic gauge from an SD in. The takeaway there was the thread down at the base of the oil filter is M12x1.5 for the fitting. (thanks to diesel911). I’ll keep an M12x1.5 bolt and a copper washer around just to plug the thing if I cannot fix my gauge.

Alternatively there are a lot of little 52mm sender gauge combos for sale out there for less than $20. I think it wouldn’t be hard to plumb a sender in with a M12 banjo bolt and use an entirely new gauge. Perhaps the modern gauge can be gutted and the motor assembly can be affixed behind our gauge panel. It’s very tempting to just redo the entire thing with an electrical system. I’m kind of bored right now and I might just take this on.

JB weld does seem to be the easiest way forward though. I can see how the solder joint would break. Every pulsation of the oil pressure resulting in a wiggle of the needle is a micro stress cycle. It must be bazillions of fatigue cycles on the bourdon tube.

Thanks for all the ideas.

ETA - another idea is to use a really powerful soldering iron to reflow the solder joint. A bit of plumbing flux will help. I’m thinking of my propane powered cordless soldering iron. That thing can pump out a lot of heat compared to an electric iron and it has the advantage of putting the heat exactly where you want it. Not on hair spring like the blow torch.

I got the dash out, and it was indeed the gauge leaking. I found another gauge in my junk box, and hooked it up to the oil line for a test.Attachment 169416

I let it idle for about 15 minutes, and the paper towel under the gauges didn't have a single spot on it. So, I started trying to swap the good gauge into my instrument cluster. Couldn't use the entire assembly, the junk box circuit board didn't have a relay that mine has. Couldn't use the set of three, it wouldn't fit my circuit board. So, I had to remove the gauges from the set of three and swap the mounts on the gauges. The gauge mechanisms were identical, but they had different mounting bars.Attachment 169417
That shows my mount on the good gauge, with the longer, straighter mount from the junk box cluster.

Then it was just a matter of getting everything cleaned up and reassembled. That didn't go smoothly. The potentiometer for dimming the instrument cluster was bad. The pot from the junk box was also bad. I didn't get the speedo installed quite right, so I can't reset the trip odometer.

Access under the dash to remove and replace the connections is miserably poor, one of the worst I've seen yet. Next time I'm under the car I'll see if I can get some more slack in the speedo cable up under the dash.

Comparing the instrument clusters
 

My instrument cluster has two black thingies on the back that the junk box cluster did not.
Attachment 169418
I'm guessing the one on the back of the speedo has something to do with the cruise control. Sound right?

The relay on the back of the three gauge cluster I have no idea about. Anyone have a clue?
Attachment 169419

My guess is also cruise control related. Search on the part # then you'll know.

The relay is a you left the lights on reminder.