Disaster struck - 350sdl threw rod!
 

Any thoughts or advice for us . . . ?

Realizing the problems encountered with the 1990 350sdl engine, my family has enjoyed driving a car we bought from the widow of its original owner.

The 350sdl had 196K miles on the odometer when I took it home. The condition of the exterior and interior was exceptional. The engine started without hesitation and with no smoke from the exhaust. It accelerated smoothly and proved to be an efficient and strong engine.

Three years later, at 232,754 miles and without warning the engine threw a rod last week. The engine is beyond repair.

The options we face include:
1) scrap the car even though we do enjoy driving it
2) replace the engine and accept the cost as part of enjoying this car.

Are there other options?
Any thoughts and suggestions will be appreciated.
If you feel we should replace the engine and can offer any advice for sourcing the replacement your advice will be welcomed.

Thanks in advance for your guidance!

Mike

Most folks recommend finding a 3.0 liter OM603 and dropping it in place of the 3.5 liter rod destroyer. Some even recommend using the head from the 3.5 liter, especially if you find an OM603 with a cracked head.
That is what I would do....
Search on here for "rod bender" and you will be reading for hours. Sorry for your troubles, they are a nice car with a flawed engine.....

If you like the car otherwise and it has no serious unfixable problems like rust, I would put a 603 3 liter engine in and keep it. You won't find a new car to match it.

What do you mean threw a rod? These engines bend rods but they don't often throw rods. A thrown rod suggests improper lubrication or some external factor. Bent rods are believed to be a design flaw.

Regardless, you are where you are. The least costly alternative, IMO, is to locate a good 3.0 liter block to replace your 3.5 liter block. It's a straight swap - everything that attaches to the 3.5 block will attach to the 3.0 block. Make sure you get a 3.0 head gasket!

Next would be an OM606 conversion. You have a choice of non-turbo from a 95-97 E300 or turbo from a 98-99. It's mostly a drop in deal if you keep the injection pump from the 3.5.

Or you can blow up to $10K for a new 3.5 block from the dealer or Metric Motors.

This will only be cost effective if you do it yourself. If you pay someone to do it, they will insist on a new 3.5 block because they don't want to warrant a potentially faulty used engine.

Sixto
87 300D

Jimmy, Jeremy and Sixto: Thanks for responding!
 

I will explore your suggestions! It will be interesting to hear my mechanic's response to them.

I do agree that it will not be cost-effective to have my mechanic replace the engine and will likely do it myself . . . with the help of two very capable cousins.

And . . . yes, Sixto, you are right. It is rare to throw a rod in this engine and would be great to explain a lack of oil as the cause. However, the night before, while topping off the windshield washer reservoir, I checked both the coolant level and the oil level. The coolant was fine, and I added 1 quart of oil to the crankcase. The oil level was fine when I backed out of the garage the next day.

What is most confusing is that the oil pressure gauge indicated the oil pressure was fine as I pulled onto the interstate . . . one mile before it threw the rod.

I wish we understood.

Thanks again, gentlemen!

Mike

Its rare but it happens, even on the ever so durable 616 and 617 it can happen without warning, especially when up in the very high miles category....something can just decide to let go.

I'd swap in a 603 3.0 liter engine as others have said....then it would last a long long time.

Scrapping is for picked over parts cars. Even with a blown engine, somebody would want to buy it as-is. Scrapping an otherwise good car is a waste.

what part of SC are you in?
I may be close enough to lend a hand.

UPDATE - After 5 months.
 

In November - 4 months after my first posting - we installed a new engine in my 350sdl. It took 4 months because finding an engine to rebuild was not easy and working only on weekends stretched out the entire project.

In August, I found a wrecked 1990 350sdl that had only 160,000 miles on the odometer.

Over the next couple of months, the engine from that car was overhauled. We honed the cylinders, replaced the connector rods with the more robust upgraded rods from Mercedes, all new bearings, rings, gaskets, cleaned injectors, ecteteras.

In November the "new" engine was installed in the car and started. When first started only 3 of 6 cylinders were firing. After considerable "coaxing" and replacing 2 injectors, 5 of 6 cylinders are firing.

The engine starts without hesitation and accelerates smoothly when entering the freeway. However, cylinder number 3 will not fire. The third injector was installed in cylinder 3 last night, and it had no effect at all.

When sitting at a stoplight or idling in the drive, cylinder 3 does not fire and a very pale blue smoke comes from the exhaust. When pulling away from a complete stop, voluminous clouds of that same pale blue smoke pour from the exhaust until the vehicle has passed 15mph.

We plan to:
1) test compression on cylinder 3
2) check the injector pump that supplies cylinder 3

Pulling this engine in order to replace rings in cylinder 3 is a big job that I would rather not have to do.

Any other suggestions?

That's what I did.

I bought a '86 SDL that threw a rod cap. The rod then broke a hole on each side of the block. Had the car shipped from Washington to to Michigan. I'm about to put the engine back together. (Once I get my sons 240D engine rebuild running, maybe today!)

All that smoke is probably the raw fuel boiling in the exhaust.

Have you tried swapping the allegedly offending injector to another cylinder and seeing if the problem follows it? Also, trace all your fuel lines and make "double-danged" sure they are connected in the correct order. This from my own personal experience of getting them mixed up upon reassembly.

Open the fuel line at the #3 cylinder and see if fuel squirts out with it running. If not, Injection Pump problems. If so, and you've succesfully eliminated the injector, the next step is to pull the cam cover to look for a collapsed lifter or check compression. You can also do a quick-and-dirty compression check, crank the engine with the stop lever down and listen for an uneven crank of one cylinder without compression.

Did the block receive a new bore and then honing, or did you just hone the "oblong" bore? Reused pistons? This is problematic with an engine prone to ovaling cylinders.

When my oil consumption reached an unacceptable level I decided the engine was about to go. Ovaling is common in the 350sdl. After considering the cost of parts and my labor ( I have the facilities for such an overhaul) I found it cheaper and more cost effective to purchase a rebuilt motor from Mercedes.
We installed it a few years ago. The product was worth the cost.
You may see the installation at www.scaffolding.com/mb

3.0 is the answer. don't scrap a good car, find a good 3.0 engine.