I have a 1982 300sd turbo which I love. Runs great. I recently came across a beautiful 1990 350 SDL (I know, the infamous rod bender) and bought it. I went against my better judgement. It was just to nice to walk away from. It has 139,750 miles on it and I just drove it 300 miles, mostly highway and it seems to run perfect.
My questions to the group are:
1. are there any of these engines that do last
2. are there any know preventative measures one can take to increase the longevity
3. is it correct that if driven mostly highway miles rather than city it may last longer
4. how long can I expect this engine to last given gentle treatment and regular oil (Amsoil marine diesel 15-40) changes
5. what will be a good replacement engine. Will the 5 cylinder bolt up to the trans and everything else, Or is there a factory replacement for this 350

The body, interior, chrome and electrical are all like new. This car rides beautifully, not a squeak, rattle, wind noise or shimmy. I'm willing to take the financial hit for a replacement engine if and when the time comes. This is a car I would like to keep for the next 10 years or longer. I do keep some of my cars for a long time. Have had (and still have) my Grand Cherokee since new in 1993 and my 1959 Tbird convertible since 1972.

Best regards,
squarebird59

Many opt to stick in a 3.0L 603 motor, it's what I would do. All of the last years of the W126 parts (seats, stereo, etc) with the more reliable six cylinder motor.

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I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

1. At least 50% of them have no problems.
2. Disconnect and plug the EGR........but.......this is just a theory.......it's certainly not "known".
3. Again, another theory.........not proven.
4. If a rod doesn't bend, it can last 400K miles.
5. The five cylinder won't bolt up to that trans. The replacement is the same factory 350 engine, or the similar 300 engine. Some folks have found a good used 3.0L engine and installed it with decent results.

the coop im in the leader bought a low mile 350SDL and this summer he is tearing the engine apart and putting upgraded rods in. its a great car just the engine design was flawed.

So you can upgrade the rods to aftermarket ones and be done with it ?

i dont know alot about the 3.5 litre diesel engine in those cars but ive heard stuff like that. and i want to say the rods are mercedes benz upgrades .. brian carlton would know more about that than me.. im an om617 person

The block is about 0.080" over MORE than the 3.0L... that's a lot for an over bore on an already thin walled block.

If your pal is tearing it down, I'd like to see the 3.5L crank in a 3.0L block.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

i have one too. 90 350.

i am not convinced that stronger rods will prevent anything. several here have had 350s with replacement blocks that bent them too.

i think it is likely to be head gasket related. i believe that the block flexes too much and compromises the seal and it leaks into the combustion chamber and when you have more than 1.5 cu in of fluid it will hydrolock and bend the rod. no rod will stand up to compressing liquid.

so my advice is to keep an eagle eye on your oil and water and at the first sign of head gasket seal failure replace it.

and if yours does bend a rod, i would rebuild with a 3.0 short block.

the idea of a 3.5 crank in a 3.0 block is intrieging but nobody has stated that it will actually work with factory parts.

good luck with it. they are really sweet driving cars and the quality of the interior bits is just outstanding.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

Oh, I don't think it can be done with stock rods... you'll have to have custom ones made if you plan to reuse the 3.0L pistons. Shouldn't be too hard nor too clostly.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

Tell me more about this hybrid motor..

You keep the 350sdl head and place it on a 3.0 bottom end ?

What modeala and years do you get that 3.0 bottom end from ?

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1985 300D : the clean one 180k miles - Now passed onto my parents.
2000 E39 M5
2002 e46 330xit
1991 mustang notch (project)
1970 chevelle (project)

Just an idea... a 3.0L stroker is what it is really. Like taking a 400 GM smallblock crank and sticking it into a 350 block... makes a 383 (with a .030" over, otherwise it's a 377).

Anyway, you'll use a 3.0L block (smaller bore) and the 3.5L crank. Use 3.0L pistons and then have some custom rods made for the new compression height. OR you could have new pistons made and use the 3.0L rods. I'd rather have the rods made.

You'd use the same cylinder head along with injectors. Probably the 3.0L IP also as it seems to have more fuel flow at higher RPM. The 3.0L blocks were until '87 I think, after that they're all 3.5... so there should be a glutton of 3.5L cranks and 3.0L blocks around that had head failure.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

You'd get the 3.0 from the '86 and '87 vehicles. The SDL and the 300D would be the models.

Wow that sounds pretty cool. Then you would have like a 3.2L 603!

Might be a nice blend of the high end power of the 3L and low end torque of the 3.5L.

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2016 Corvette Stingray 2LT
1969 280SE
2023 Ram 1500
2007 Tiara 3200

Basically what I see.

__________________
I'm not a doctor, but I'll have a look.

'85 300SD 245k
'87 300SDL 251k
'90 300SEL 326k

Six others from BMW, GM, and Ford.

Liberty will not descend to a people; a people must raise themselves to liberty.[/IMG]

personally i would stay with stock 3.0 components. tried, proven, available.

i did think about this myself, and it has attractive points, but i wouldnt in the end.

my $.02

tom w

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.