I have the opportunity to buy a outstanding example of a 90 350 sdl. Now I know all the hits on the 3.5l motor, mostly flexable connecting rods, my question is, the earlier cars have the 3.0l motors which are much more reliable and essentially the same block, I believe, could one replace the 3.5l engine with the 3.0l block and the 3.5l accessories, like turbo, injection pump, exhaust, electrics etc, anybody done this? Any reasons why it would not work? Any drawbacks? THX
Ron

I think the IP would be different. It has to inject more fuel per power stroke to take advantage of that extra .5L If you put it on a 3L it would result in overfueling (i.e. smoke).

Also, why swap right away? Drive it until you start getting problems and swap it then. Just enjoy the extra power until it does bend a rod.

How many miles? Believe it or not, if it's got under 100k miles, don't touch it. If over 150k or so, you SHOULD be ok as most of the motors grenade before 100k.

Use Mobil 1 or Mobil Delvac 1 only -- should last forever. I've read reports by an experienced tech that the 350 run on full synthetic lasts as long as the 3.0L 603, the ones that died were all run on dino oil.

I'd not do any swaping unless it bends a rod, no need to panic.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!

ohcaptainron,

I am not sure what the "rules of thumb" cited are based on, and, considering my experience Mercedes-Benz is not about to reveal the causes and facts. My 1991 350SD was at about 160,000 miles when symptoms started, and by 162,000 I had it in to rebuild the engine. I bought the car with 75,000 miles on it expecting it to last for several hundred thousand miles, and I never put anything but Mobil 1 15W-50 in the engine. I changed the oil on a regular basis, usually every 3,000 or 4,000 miles and never went longer than 6,000.

On the other hand, if you get one of these cars in great shape for a good price, and you are mentally ok with the potential for the engine to suddenly die, you may be very happy with the car. Until the engine failed, I was extremely satisfied with the car - great ride, lots of room and very good mileage. I was not ready for mine to die when it did and will never feel a newer Mercedes-Benz is quite the machine the older ones were.

I know that sounds like a cliche' but some of those '70's and '80's cars were just as close to bulletproof as a car can be, simple maybe, with fewer gadgets, but unbreakable. I am often struck by how we have come to accept or even demand useless gadgets in our cars. It is at the point where the engine, transmission and chassis are taken for granted and hardly affect the selection process of a new car buyer. The car itself is now merely a means to sell electronic junk that no one would buy if it was not in a car.

Given knowledge of the issues here, you can make an informed decision. That is a better position than most of us with first hand experience with the 3.5 liter Diesel failing were in when we bought. Good luck whichever way you go, Jim

__________________
Own:
1986 Euro 190E 2.3-16 (291,000 miles),
1998 E300D TurboDiesel, 231,000 miles -purchased with 45,000,
1988 300E 5-speed 252,000 miles,
1983 240D 4-speed, purchased w/136,000, now with 222,000 miles.
2009 ML320CDI Bluetec, 89,000 miles

Owned:
1971 220D (250,000 miles plus, sold to father-in-law),
1975 240D (245,000 miles - died of body rot),
1991 350SD (176,560 miles, weakest Benz I have owned),
1999 C230 Sport (45,400 miles),
1982 240D (321,000 miles, put to sleep)

Ohcaptainron,

I agree with not replacing the engine (NOT MOTOR) until necessary. It may never fail. If it ain't broke, don't fix it.

But if you do replace the engine with a 300 SDL engine, I would put the 300SDL engine in as is and not change any parts especially the injection pump. All the parts are designed to work for the 3 liter engine. Maybe one of the parts you change is the part that makes the 3.5 liter engine fail.

P E H

Do you have access to the records to see if any engine work was done in the cars infancy?
Some of these cars had engine work done at 30-40K
(shortblock)miles
If thats the case you should be fine

but then agian the car may run for a million miles..some people never had any issues....I always wonder how that is

but seems to me if you change out to the 3.0 you will experience a loss in power...the last 300SDL I drove definitely had less power than my car and was pulling less weight
Also I think 3.5 liter is a quieter engine also

the MB zone rep told me some years ago it was a fuel issue...although I am not sure where the "bad" fuel was
One thing is for sure if the car is that old or has over about 75K miles expect no help from MB


good luck


Warren
1992 300SD 168K
Columbus Ohio

Less torque, less throttle response, but more top end is the case with the 3.0 liter. It redlines much higher, too.

the 3.0 liter is a "screamer" while the 3.5 focuses on torque.

3.0 liter equals fast. 3.5 liter equals quick.

quick is to acceleration as fast is to top speed.

__________________
1987 300SDL (324000)

1986 Porsche 951 (944 Turbo) (166000)

1978 Porsche 924 (99000)

1996 Nissan Pathfinder R50 (201000)

If one buys a "350" that had the engine replaced 55,000 miles ago with a MB factory engine , what if anything, could be done with MBUSA regarding reliability if the engine dies.

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

Short block replacement has a 12 month unlimited mileage warranty...long block replacement(as mine was) give you another 4 year 50 warranty just like the car was new

If the engine work was done by a dealer you might get some assitance after the warranty period by MB...but I would not count on it.
I have been told they they have NEVER had an engine issue again with an engine that was installed at the MB dealer
I think one of the kickers here is that it seems they they kept replacing/updating parts on this engine...so the engine that was replaced in 1996 might have had a serious update from one that was replaced even a year later.
The tech who installed my engine said there were several differences in the new long block and the one he was pulling out.A very much different cylinder head for one thing and the engine shock design and assembly

As for the increased torgue of the 3.5 liter..I need it since I am driving a 140 vehicle

This one is a 140 too. The engine was put in less than 4 years ago but has just passed the 50000 mark. It is running fine. I am just curious as to how MBUSA would react. I am the third owner, second one on this engine.

__________________
N. Hodges
1994 S350
1987 300 SDL (for sale)

I would imagine you would be just fine

buy FYI I think MB has really "tightened" their belt on goodwill warranty work...guess they decided it was too expensive
Especially since no one else was so liberal on goodwill work after warranty


Warren
1992 300SD 168K
Columbus Ohio

That is a bizarre discussion--putting a smaller and slower engine in a car. I'm having hard time understanding why anyone would want to get involved in that.

I always thought it was inappropriate to put synthetic oil in an older car or one that hadn't had it early on?

Not so bizarre when you consider that the 603.96 was standard issue in the W126 until the 603.97 came along. Even less bizarre when you consider the cost of a replacement 603.97 vs a replacement 603.96. Could be the difference between a hunk you donate to a wrecker and something you can get running for under 4 figures. It's gotta be better than a small block Chevy swap

Sixto
95 S420
87 300SDL

There are far more 3.0L 603 engines around than 3.5L, and I would certainly entertain the idea myself -- the 3.0L has plenty of power, and the cost would be about half. I believe a crate long block 3.5 is around $9000 from the dealer, you should be able to find a running 3.0L for $3000 or so. Rebuild cost for the 3.5L will be in the $6000 range for parts, plus about 50 hrs labor, more if the head is in need of work, abint the 3.0L is cheaper since you won't need to do the rods unless bent (although that is the main reason why the 3.0L need rebuilding).

They are physically the same size, so installation is a breeze.

If you were really desperate, you could swap in a 617, too, but that would likely be a major undertaking, probably need a driveshaft custom made.

You could also forgo the diesel altogether a stick in any contemporary V8, too, as long as you swapped the exhaust and computers.

The real Achilles Heel of the W140 chassis is the electronics -- they don't last, and are expensive.

Peter

__________________
1972 220D ?? miles
1988 300E 200,012
1987 300D Turbo killed 9/25/07, 275,000 miles
1985 Volvo 740 GLE Turobodiesel 218,000
1972 280 SE 4.5 165, 000 - It runs!