If you ignore the later 6 cylinder ones then I'd say they are among if not the
most reliable engines MB ever built.

I've got an early  80's w123 diesel and my brother has a w123 and w126 diesel, excellent cars. Mine has about 500,000 kilometers and
it can take other cars when the light turns green, don't know why that is, as my brother's car is slow.

Any time I take taxis (w124 diesels or newer ones) in Europe I ask the drivers (mainly in Germany) how many kilometers their cars
have and it's always between 700K-900K kilometers, they say that no engine or transmission work was done, don't know if that's true
but my father's w124 200D sure makes it seem as possible.

WELL maintained MB diesels of any age are the most reliable cars ever built. Period. This from the experience of MANY people around
the world.

cp

The 1979 to 1985 300SD model has a 5 cylinder 120 HP turbodiesel, I've
owned one of these since new. The 1981 or '82 300D model has the same 5
cylinder engine as the SD model.
The 300D models up to '81 or '82 have a non-turbo 77 HP 5 cylinder diesel.
The 240D has a 68 HP 4 cylinder diesel. The 240D is the simplest model
but underpowered, IMHO. Be sure YOU can live with its low power before
you buy a 240D - manual is better than an automatic.

All the above engines are tough and durable engines but have old
technology. That means more maintenance than say a '05 car. Oil and
filter change every 5K miles, their valves ought to be adjusted every
15K miles, transmission oil and filter change every 35K miles. These are
not physically hard jobs for an organized DIY owner; parts and supplies
are easily available.

So their reliability depends on the maintenance level - shortcuts are
just that, and don't count.

During my commuting my 300SD delivered 24 mpg city and freeway.

Very reliable.  I have a '79 W123, originally a 240D, now with a 5cyl.
turbo out of an '83 300SD.  Only reason the engine got swapped was the
oil pump on the 240 croaked...and took the engine with it.  Easier to
swap for my friend's 300 turbo than to rebuild the 240.

Manual tranny is definately better in the 240.  They are rather
underpowered for that heavy a car.  Rated at 67 hp, I think.  If you are
just doing city driving, mostly flatland, it's probably not an issue.
My dad drove it for years in the Silicon Valley area with no problems.
I live in the mountains however, and I REALLY like the extra horses that
the turbo gives.  I don't feel as if I'm going to be the hood ornament
on a Kenworth now <G>.

I get around 24 mpg average (US), not much variance with city or highway
milage.  The only major difference I noticed was when I was able to get
biodiesel.  Went through about a years worth and was getting 26-28mpg.
Shrug. Don't know why, but the old girl really likes the biodiesel.

Rochelle
(looking for another station that sells biodiesel...)