Ha, it's definitely painted and yeah it looks waaaay better in pictures than in person

But yeah, the car is in pretty good shape considering the most recent owners neglect. The original owners seem to take very good care of this car.

I have changed the oil to Rotella 15w-40, as well. Seems to be pretty universally liked.

Replaced the fuel filter today. The last person to do so did not use a crush washer on both sides of the banjo fitting. After replacing and putting a new washer on either side of the fitting, the car runs great! Feels like it has more power. Makes me wonder if it was being starved slightly by the holes in the bolt being slightly obscured.

Anyway, filter is in and no leaks. Unfortunately I'm pretty sure the accumulator is done for, as I have to crank the car a few times before it'll start each time. I have a Bosch on order and will install it next week.

More good news, the rear self-leveling suspension pump still works! The bushings in the valve control rod have deteriorated entirely, meaning it was just dangling beneath the car. I've ordered a new one and will install it while i'm under there for the accumulator. No idea if the system functions correctly or not yet, but for the moment I will just remove the fuse until I have the linkage replaced.

In addition the fuel looked clear and free of contaminants, leading me to believe the tank is at least mostly OK.

It also looks like the flex discs on the driveshaft are in decent shape, don't look dried out or cracked.

Out of curiosity, and because I keep seeing conflicting information online, why is 15w-40 recommended for the m103 engine? Why is a full-synthetic 10w-30, the factory weight, not sufficient for these engines?

It concerns me slightly as I do not like the idea of driving long highway distance with the car at 3.5k rpm (75mph, just about) with an oil that is too thick. Wouldn’t that just be another contributing factor to early head gasket issues?

Any insight would be welcome. I’ve googled quite a bit, cannot find a good reason to use thicker oil other than “I do this and it seems fine”

Thanks

In the 80s, nearly all Mercedes engines said 15W-40 for diesel and 10W-40 for gasoline. Finding 10W-40 for gas engines is getting difficult and they have removed most of the zinc additives that helped protect flat tappets and cam followers. The diesel oils still have those additives, although at a lower concentration than they used to. The other benefit of running diesel oil is the stronger detergent package they use. In an older engine, it'll help clean out any accumulated sludge and keep it suspended in the oil until your next oil change. The 15W-40 Rotella is also cheaper by a significant margin than a similar gasoline rated oil.

It all comes down to personal preferences. The factory weight oil was 10W-40 through the 80s and into the early 90s.

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Mercedes fluid spec sheet (in the owner's manual packet, if you have it) will likely specify 10W-30 as OK up to ~85F ambient temps. With the M103 known to drink oil, using a thinner oil will only increase consumption. Here's the 1994 MB approved engine oil viscosity chart:
http://www.w124performance.com/docs/mb/other/MB_1994_Service_Products.pdf


Diseasel300 is correct about the reduced level of zinc & phosphorus (ZDDP) in most newer oils, however this is dictated by the API rating (SL, SM, SN, CI-4, CJ-4, etc). Newer oils, both gas & diesel, have reduced ZDDP levels. If you want higher ZDDP (generally 1100-1200 ppm or so, vs the 800-900 in the new stuff) you will need to do research on the oil in question. In general, most diesel oils (Delvac 1300, Rotella, etc) still had decent ZDDP levels. However, the latest diesel spec CK-4 may have even lower levels, and it may vary based on viscosity. A bit more info here:
https://pqiablog.com/2017/04/24/results-in-on-four-api-ck-4-diesel-engine-oils/

There is NO issue driving long highway distance with the car at 3.5k rpm with an oil that is "too thick". It would NOT be another contributing factor to early head gasket issues. The M103 in general doesn't have head gasket issues (that's the M104 DOHC engine), the M103 has oil consumption issues due to weak valve guides... IMO.

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Alright, been a while and I don't have pictures, but here is the list of improvements since last post:

• Rear main seal was leaking and is now replaced
• Replaced air box with one without broken clips
• Replaced headlight covers with Uro bits
• Replaced single-pump washer tank with double-pump washer tank and lines
• Greased / cleaned windshield wiper mechanism, works great now
• Oiled cabin air motor, no more squeaking
• Replaced non-functional dash switch gear
• Replaced entire instrument cluster wit one that wasn't grody
• New tires all around
• New front-right inner moog tie rod

Few other small things have also been taken care of. The car is still boaty, needs new shocks / springs, but I am not going to mess with those yet.

Next Steps:

• At the moment, the biggest concern is a "rumble" noise that comes from the back of the cabin under acceleration or while at speed on the highway. It is quite pronounced, and getting worse. The flex discs all look good, but a small google has lead me to believe the driveshaft carrier bearing might be at fault, or perhaps the rear diff.
• While replacing the driver-side door panel, I noticed that there is a plug with three wires going to the door lock mechanism. The plastic of the plug is so grody it's just falling apart, meaning the wires are barely held in. The wires themselves seem to be in OK condition a bit down from the plug, so I'd like to just buy a new plug and splice new wires into the existing harness. Alternatively I can just solder the wires directly to the female connectors and just heat-shrink around them.

Thoughts?

Also gsxr, thank you for your post on oil! I've switched back to Rotella-T 4.