Since my 1990 420SEL died I'm looking for a new toy. I found a very nice condition 1992 300SD for sale about 3 hours from me. The seller has been great with answering questions for me since I'm not close. I attached a video link of the car running. https://youtu.be/up17lyYUHtE

It sounds good to me, just wondering if some experts of these think. The body of the car has over 250k on it, but the "rod bender" engine was replaced by mercedes with a new engine about 15 years ago.

One issue I know that it has is that the speedometer doesn't always work. The ABS light is also on. The seller said he tested the wheel speed sensor in the back axle and it doesn't continuously work. He said the signal cuts in and out. Would that be a good starting point to knock out 2 birds with one stone?

I also know about the engine wiring harness issues. He said he fixed a bunch of stuff with it but that's something I might just fix on my own also if I end up getting it.

__________________
2022 Nissan Frontier Pro4x
1990 Mercedes 420SEL
1950 Packard 8

Previous German cars-
2001 Mercedes SL500
1983 Mercedes 300SD
2011 BMW 328i (manual)
2008 BMW 535xi (manual)
2006 BMW M3 (manual)
1980 Mercedes 300TD
2006 BMW 750i
1996 Mercedes E300D
1994 BMW 740i
2006 BMW 330xi (manual)
1999 E300DT Smoke silver/black 253k
2012 BMW 535i Xdrive M-Sport
1984 300TD-T 304k
1988 Mercedes 560SEL (parts car)
2010 BMW 550i xdrive
2017 Audi A4 Presitge
1979 300SD 313k
2003 E500 189k

I have a 93 300d that sounds better that I may let go if you’re interested. Not ruined with K&N filters… and a proper factory rebuilt engine and AT. AC works.

The w140 is a different beast. A more complex one. If something goes bad it’s involved. That one has the same 3.5L rod bender as my two w126 350sd and my 93 300sd. Not a matter of if but when a head gasket will fail. Chances are if it has 25, the engine was replaced or at least a HG was done.

It sounds like it has some bad lifters and/or injector.

But the 603 is a well understood engine, and there is a good community of folks keeping up w140 cars over in ‘world.

__________________
Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

I forgot to add that after the engine was replaced the current owner did an EGR delete. They are a diesel shop and he's been using as his daily driver for the past 2 years.

It would most likely be a hard pass for me for any car with one of those crappy air filters on it. And no it does not sound as quiet and smooth as it should be. Could be something minor or something major. It sounds just like the one I have that had a bent rod. I replaced the rods with the upgraded rods but the #1 cylinder was already showing wear. I think it might have barely been within limits but compression on that one was always a little low. Sounded just like this car but still runs fine. Oil consumption is about a qt every 500 miles. I have another one that has a factory replacement engine in it. That car is SUPER quiet and smooth. If this one had a new engine, was it a factory crate motor? You would know because it would not have a serial number on the spot in front of the IP and it would have torx bolts instead of hex. Then there is the issue of that air filter. What dummy puts those things on? The factory air filter assembly is great, pulls in clean cool air from outside the engine compartment instead of hot air from under the hood. These also do not filter very well allow dirty and dust to get sucked in causing more wear.