Would you be afraid of a 350 SDL?
 

A few have popped up for sale lately, I have always heard about the rod bending but not sure which ones, or the exact reasons leading up to it. I read somewhere that those that made it to 75K seem to be OK, but who knows where that came from? I only know one person who bought one, an independent Mercedes mechanic I knew. He left Tucson for Albuquerque with it and threw a rod before he got there.

I wouldn't be afraid of one because I wouldn't own one. Too many fiddly vacuum bits for the emissions controls, 350SDL specific driveshaft and engine mounts (which are very expensive), an ASD system that's a "meh" afterthought to adding traction control, and of course an engine that has weak connecting rods and an appetite for head gaskets. There are people out there that love them, but if you're not in the market for some potentially expensive repairs with hard-to-obtain parts, look for a 300SDL if you're wanting the LWB 126, or consider building a 3.0L 603 or 606 to go in there.

I loved mine...
 

I owned a 1991 350SDL. It was the smoothest and quietest running Mercedes I’ve ever owned. Yeah, I always had the rod bending fear in the back of my mind. A friend of mine wanted it more than I did and so I sold it to him. I don’t think there is a “safe” mileage to say that the rod bending doesn’t happen. It could happen at any mileage IMO.

I am half way through reading a very long thread on the 350. It is discouraging for the most part but then there are people popping in with high mileage and no issues. Too bad, there is a real low mileage beauty for sale here right now

https://tucson.craigslist.org/cto/d/1990-mercedes-benz-350-sdl/6406123948.html

Honestly no, I saw one in my city two days ago, I was driving right beside it.
They had the wrap around euro tail lights, it was a clean car too. Wish I had one.

Holy hell. I don't think even a Concours-ready model could get that kind of dough.

WOW! I should have held out selling my 350SDL a couple months ago. It was a very nice low mileage (120,000) example, I got $4,800 for it. I had all the service records since new, and no record of anything major like connecting rods. It was also white with grey interior......Rich

I wouldn't be afraid of it. If it made a 100k miles without bending a rod, it probably isn't going to anytime soon. I'd love the bigger turbo, beefier head and crank in my 87 300d.

The w126 300SDL with the updated interior, long wheel base is such a gorgeous car. Not a 8k gorgeous car. I don't think I'd pay anything more than 4k for any Benz between 1978 to 2004 since nice examples can be found cheap for any mercedes.

How different is 603.970 emissions from .96? .971 has vacuum boost control. Convert to pressure control when you lose boost.

Do most 350s out there have ASD? Most I see here don’t have it. But I agree it’s poorly designed because it’s dufficult to bypass when it stops working properly.

Sixto
98 E320s sedan and wagon

Nothing drives like 'em but between the connecting rod/hg issues and some parts being unobtainium, I walked away from 2 350SDLs (prior to buying my 91 300D).

I agree with Ben.

I had one for a while. it was not real high mileage, needed a valve job, had the intake clogged with semi hard black goo, and might have had the beginnings of a bent rod. It drove like a dream with bags of torque and reasonable economy, an excellent interior. I eventually sold it along to BC and bought a new Magnum.

I don't think there is a safe mileage to get past and I don't think MB ever truly solved the problem. they built it maybe six or eight years and eventually stopped building it.

I'd buy one if I could get a really clean one cheaply enough to put in a nice tight 3.0 liter motor and not be underwater.

I would probably roll the dice if I could get it for 1/2 that. Unlikely though, I Googled the phone number and it is a local dealer. They are asking NADA high retail. They will probably sell it to someone who doesn't know anything about the reputation.

They have that stupid vacuum wastegate for one, several of them seem to have the ridiculous ARV in the turbo outlet, different prechambers and injectors (which are actually a bonus in this case), I'm sure there's other things too. More vacuum gadgetry = more headaches.

It seems like a lot of the '91 350s have ASD. Not sure if they made it a standard feature right before they discontinued the car or what. '91 was a weird year with a bunch of 350SDL exclusive parts and options.

I have owned a 1990 350 SDL and had no problems relating to the engine. I do have issues with the monovalve which I replaced on the recommendation of a mechanic who was "clairvoyant" and knew that this was my problem (not).

At this time engine rod issues can be solved with the 3.0 liter lower or short block. Having to possibly deal with this at some point should be reflected in the cost of the car though. Really kind of a white elephant model in todays market.

All the S class models with the 3.5 liter engine, so both 126 and 140 models. I think the cut-off for the 3.0 liter engine in the 126 is 1987?

The root cause seems to be faulty head gaskets + weak connecting rods. The MB replacement engines have improved head gaskets and rods.

If a car doesn't have a documented replacement engine from MB, it will need a new head gasket and if you want complete insurance to make the engine as long-lived as possible, replace the connecting rods as well. Keep all documentation to prove this work has been done in the event you want to sell the car or the engine later on.

Another very reasonable "upgrade" is an OM606 turbo engine from a '98 or '99 E300 Diesel, but keep the OM603 3.5 liter injection pump and associated throttle linkage. OM606 has 24 valves and an intercooler, so a big jump in power compared to the OM603, and better fuel economy.

I did a lot of thinking about the issue of the Rod Bender along with some pretty smart fellows and believe the issue was more due to the block being compromised by the larger bore of the 3.5 version. The flexibility of the block would precipitate partial failure of the head gasket allowing in enough liquid until the rod is bent by a partial hydrolock.

it only takes a bit over a teaspoon of liquid in the combustion chamber to fill it and cause partial hydrolock.

My roommate has a 1991 W126 350SDL as a daily driver. The original 3.5 engine died and it was replaced with a 3.0 from a 1987 W124 300D, which was a good choice.

It has ASD and I just got done rebuilding the tandem power steering pump. Keep in mind that rebuilt tandem pumps are VERY expensive, and I don't think you could buy a rebuild kit if you tried. My roommate and I scoured the internet for a long time and everyone that said they had a kit ended up coming back saying that they are no longer available. We finally found a place that had two older stock kits left and bought them both.

This one came stock with a parallel-flow condenser (it actually has a part number in EPC). Overall, it's a nice car, but it has a few parts that are impossible or expensive to buy new, and the same goes for finding the parts used.

For example, the plastic coolant reservoir is special to the 350SDL as it's skinny and long. Expensive. The radiator is specific to the 350SDL and it's not available new ANYWHERE for any price. So, you have to repair the old one, install a used one, or have one fabricated.

If you buy one, be prepared to replace the block or entire engine if it suddenly fails. Also make sure to have extra money on hand for those 350SDL-specific parts as they can be pricey. The transmissions are also prone to losing reverse due to having springs that are too heavy in the reverse clutch pack. All that aside, it's probably one of the best W126s made, and will likely be the most valuable model due to the low production numbers and remaining survivors, not to mention they sip fuel unlike the big V8 models.

Are you sure? I’ve only seen ARV in ‘87s and ‘86s with a trap oxidizer. I hear not all ‘86s had a trap oxidizer. There’s no trap from ‘90 so they shouldn’t have ARV either. 140 SDs don’t have ARV. Certainly my ‘93 SD didn’t have ARV.

Are you sure also about boost control? IIRC 90-91/.970 don’t have a MAP sensor so they can’t have vacuum boost control.

Sixto
98 E320s sedan and wagon

Not 100% on any of it, information seems to be hard to come by due to the low production volume. I don't own a 350 and don't plan to. I can confirm that '86's came without the ARV and trap oxidizer, mine's one of them, and a late production '86 at that. Not sure what the big differences are between '86 and '87, but the '87's seem to be more common despite lower production numbers. Weird...

I've owned a 1990 350SDL for 18 yrs. It just rolled 200,000. I bought it with 95,000 miles. Factory rebuild @ 75,000. The car is magnificent.
My only failure was a crack in the power steering pump mounting.

An all aluminum radiator specific to the 126 350SDL is readily available for $272. The overflow tank is $190. ;)

Where are you finding the radiators for sale? It will be the first time I've ever seen one available. $190 isn't too bad for a coolant reservoir. I've seen them at well over $200 before. Even over $100 used.

https://www.*********.com/gbproducts/WC/6243-01034899.html?utm_content=YN&utm_term=1990-1991+Mercedes+350SDL+Expansion+Tank+Genuine+90-91+Mercedes+Expansion+Tank&utm_source=google&utm_medium=ff&utm_campaign=*********+Google+Base&gclid= EAIaIQobChMIx8vf3pGF2AIVSEwNCh16tQwiEAQYASABEgLH_fD_BwE&ad=47433948732

Oh, wow! Those must have just become available. Very custom-looking, but it seems like they are a direct bolt-on and without the awful plastic tanks. Thanks for sharing. My roommate's 350SDL has a large area that was filled with JB Weld and replacing the radiator would be a good idea.

There are lots of threads in the forum about people not being able to find radiators, so they've been using universal-fit ones and fabricating brackets.

I own a 350SDL, well hybrid, motor from 300SDL. My guess OEM failed as tech told me who had maintain this car for 15 years for the previous owner.
When I was replacing headlight/lights switch, so I found no bulb for ASD system in my cluster, since I removed cluster to replace this switch.
I put bulb and light will not go away. I guess it doesn't work or disconnected since motor from the 300 SDL - OM603.961. Look at my signature. But car pulls nice when it warm up.

this guys got two of them

https://newyork.craigslist.org/lgi/cto/d/1991-mercedes-benz-350sdl/6416095172.html

https://newyork.craigslist.org/lgi/cto/d/1991-mercedes-benz-350sd/6415768764.html

I can't seem to load the website for the expansion tank
www.*********.com $196.48

google 1990 Mercedes 350sdl expansion tank;)

They look clapped out.

It's the "They run forever with no maintenance for 1 million miles!" guy again...

I don't want to hijack the thread, but i logged on tonight with the same question in mind, as i found this car in Houston.

https://houston.craigslist.org/cto/d/1991-mercedes-350sdl-turbo/6420105471.html

European Delivery Benz, Euro seats (no leather), looks like it is in mint condition. Trans rebuilt, but nothing on engine.

My dad wants to have a Bug out Benz, that he will drive very little, but can start up if an EMP goes off. he can either go all out and get this nice beauty or go ultra simple with a 240D manual (like me :))

Where does it say the tranny was rebuilt?

Well... maybe that was another car that i confused this one with. Sorry and good catch.

The owner of that car is a member of this forum. I think the name is HoustonM3?

It looks like a very nice car. There are some posts about it, as well as an ad somewhere in the for sale section.

-Chris

It is a very nice car....and sooooo tempting. I really like them but still don't want to pay a lot for one due to fear of the rod bending issue. I don't know why I am attracted so much to the riskier ones, I've considered a 6.0 Powerstroke as well.:(

The 6.0's can be fairly reliable engines if you correct the stupid crap Ford messed up, or buy a later one with a lot of the bugs worked out. The one to avoid at *ALL COSTS* is the 6.4. That thing was a turd from day 1.

Supposedly the #14 head is supposed to be unreliable, but so far mine's lived a hard life and still going fine.

On the other hand, the SL is supposed to be a reliable engine in a reliable chassis, and I've yet to take a trip in that car without something breaking or having some sort of breakdown. It's never left me stranded, but it sure spends a lot of time sitting waiting for parts. I've had the car for 19 years and never completed a journey without incident.

Reliability is all relative and subjective...

That Euro might be a 3.0. I don't think the 3.5 was sold anywhere but in the usa.

The SDL was a US/North-America model only. The 3.5L replaced the 3.0L in the 1990 models (hence the 350SDL badge)

So, you think its a 3.0?

They might get it looking like that. If it runs well with no noticeable issues (probably does), someone will be tempted.

Unless the engine was replaced with one from an earlier vehicle, it will be a 3.5

I knew that car looked familiar:
http://www.peachparts.com/shopforum/mercedes-cars-sale/385420-1991-350sdl-smoke-silver-creme-beige-velour.html

350SDL
 

Wow, that looks like a well kept example. I soooo miss mine. I still have the totaled car with an engine that had the top end rebuilt shortly before its demise...:cool: Temptation!!!

I wouldn't be afraid of it, but I would have to have it fully checked out for that kind of money. I'd probably prefer a 1990 350SD instead. No real reason to have the long-based model to me.



.

I agree about having it checked out. Does anyone on this forum know of any local mechanics that could perform a thorough PPI?

From all the reading I have done in the lat few days this does not look like a problem that can be forecast. It can be fine one day then show symptoms the next, and go quickly downhill from there.

Sounds like a eurospec to me.

See post #41 with a link to the car's discussion on this forum. It's a 3.5.

I never heard of velour seats being optional in the us. Never seen them in anything but a euro car. Looks like its a 3.5....too bad.

I'd kill for cloth seats in my SDL. I absolutely hate leather seats, especially in the summer. When you're already hot and climb into a 180˚ car, hot leather pressing the sweat against your back and keeping it there is not a pleasant feeling!

Interesting, first I'd heard that. Makes sense, especially if you live where 100˚ days are not uncommon. I'm guessing the one reliable way to get them would be to source them in Europe somewhere, and that wouldn't be cheap (Capt. Obvious to the rescue). Reason I even think of it, I gather that one could get a used OM606 more easily in Europe than here. God only knows how much that would cost all together.