PeachParts Mercedes-Benz Forum - View Single Post - Which Mercedes diesel engines should I stay away from?

Jeremy5848 · #77 07-31-2011, 01:57 AM

Quote:

Originally Posted by okto

Jeremy, what car have you been looking at? Maybe if you've been working on a Mini it looks roomy, but that is one big engine shoehorned in there. It hits the firewall at the back, and there's about an inch and a half to the radiator in the front, not to mention how everything exterior to the block is Tetrised in.
Look under the hood of a W123 and tell me the E300D's engine bay is "roomy".

I'm also mystified as to why you'd want to ditch the bulletproof DOHC 24V 606 for the less-reliable SOHC 12V 603.

Okto, you make some interesting points with which I will find it hard to argue (but what the heck . . .). Yes, the I-6 engine hits the firewall but so does the I-5 in the W123 model 300D (but there's not much back there to work on anyway). My '85 300D (CA version) had a pretty busy engine compartment, especially on the exhaust side. At least the trap cat forced the turbo to be up where you can get at it; in the 124 chassis the 603's turbo is buried. Overall, comparing pictures of my '85 and '87 300Ds, both are crowded on the right side and roomy on the left side. Interestingly, my 606NA is the opposite.

The main advantage of the OM617 engine is that it has the air intake and exhaust on the right side, leaving the left side relatively uncluttered. In the 60x engines the IP is lost under the intake manifold and the glow plugs are similarly buried. The 606NA is quite clean on the exhaust side -- dropped tools on that side fall to the floor, or would if the belly pans were off -- but it's pretty crowded on the intake side, much more so than the 603 engine in the 124 chassis.

I suspect that the relative roominess of a 123 engine bay is a function of which engine is in it. I don't have a good mental picture of an NA 61x because I've seen so few but the 617 turbo in California trim is very crowded on the exhaust side, more open on the intake side. Either way, it seems to be a very "busy" engine with wires and hoses and linkages all over the place. The 60x engines just seem cleaner, making the engine compartment look less cluttered. Maybe that's what I really was thinking of when I said "crowded."

As for the relative reliability of the 606 vs the 603, it's mostly a matter of the alloy head learning curve at Daimler-Benz. The later 606 engine got all of the improvements that were gradually introduced in the various versions of the 603 head. Additionally, the 606NA engine is less stressed than the turbo 603. [Did Europeans and other who got 603NA engines have the same problems?] A 603 with a late-model head and head gasket should be just as reliable as a 606. Both are similarly vulnerable to overheating, I suspect. I haven't heard bad things about the 98-99 turbo 606 so they must have learned their lesson.

In any case, my preference for the 603 turbo over the 606NA is not so much for reliability as for performance and DIY-ability. The W210/OM606NA is much more electronic than the W124/OM603 turbo and the 98-99 turbo 606 is even worse. In California, '98-up diesels even have to be smogged (biannually)! One of the great joys of an older diesel is not having to smog it. The turbo 606 is even more powerful than the turbo 603, of course, but I've never driven one. It would be interesting to put a turbo 606 in a 1995 W124 chassis but I think the electronics are difficult to eliminate. Pity.

It's late. I'm tired. Good night.

Jeremy