350SD, SDL and S350 Engine Problems http://mbca.cartama.net/showthread.php?t=25313&highlight=s350 Originally Posted by GeorgeMurphy From my files - some a little dated: At a recent Tech Session I had a chance to speak with Tom Ischler, who is a TechRep for MBUSA. I asked him to speak with me not as a representative of MBUSA, but as one car guy to another. I asked point-blank: What is MB's position on the longevity (or lack thereof) on the 603 engines. His responses were rather illuminating. He indicated that the "bent rod" syndrome and the premature cylinder wear problem were actually the same problem at different times in the life of the engine. I won't do justice to his explanation of the issue, but he broadly stated what MB believes to be happening is that the 603 experiences severe detonation due to the lower cetane fuels used in North America. In Europe, 60 cetane is not uncommon. In US markets, 50 cetane is very rare, and low-40's is common. This leads to detonation (pinging, were it a gas engine) after the piston has passed TDC in the ignition cycle. This detonation leads to the bent rods that many 603 owners have noted. The rods, once bent, subtly change the angle of the piston and this is what leads to the "egg-shaped" cylinder syndrome where the oil consumption increase becomes noticeable. What's interesting is that a compression test (hot or cold) will not absolutely indicate a problem bent rod; compression may still be within acceptable limits in spite of impending or existing internal damage. As a semi-static test, the compression is within spec even though the rods have begun to collapse. A compression leakdown test is flawed for the same reason; it is typically conducted at TDC when the piston is beyond the cylinder deformation. The reason that MB pulls the head as a diagnostic action when 603 problems arise is to determine if the problem is related to unsatisfactory maintenance (i.e.: scoring of the cylinder walls due to poor maintenance). Of course, once opened up the cylinders can be measured to determine if the "egg-shaped" syndrome has commenced. Anecdotally, he mentioned that placing a known-good rod next to a "bent" one does not reveal an obvious problem. The bending does not appear as a flexing of the rod, but it can be measured. Finally, I pointed out to Tom that I had never known a 603 owner who did not experience the oil consumption problem within the first 100K or so and that MB seemed to be very evasive about owning up to the design flaws. He stated that the policy was that owners complaining of 603 oil consumption problems were handled on a "case basis" (taking into account the maintenance history, owner history, etc...). There is, apparently, an MB form (that all Zone Reps have access to) that must be sent to MBAG to approve an MB-covered engine replacement. Tom stated that he had never heard of a request for replacement that had gone all the way to MBAG that was denied. He also stated that at 800/FOR-MERC, processes had been put in place to handle complaints related to the 603 engine. From official Mercedes sources, this is what we know: In October 1990, shortly after this motor (the 603.970) went into production, MB revised the configuration of the head bolts in order to strengthen the entire assembly. When the 1992 version (the 603.971) went into production, changes were made to the head gasket. Clearly MB was concerned about the ability of the head and gasket to withstand the greater stresses caused by the increase in displacement. Of course, essential to the motor's viability are the capacity and integrity of the cooling and lubricating subsystems. In search of the best explanation for our problem I have combed through the archives of the various on-line discussion groups of the MBCA and several other groups. I have obtained and searched through the AllData CD-Rom containing the Technical Service Bulletins (TSBs) for my particular model year. One of our members has shared with me an 'unofficial' acknowledgment and explanation given to him by an MB Tech Rep. The most specific material that I have received so far comes to me from a concerned member. It consists of a service advisory (I'm not sure of the precise title) contained on microfiche. It appears under a group captioned "Removal and Installation of Engine, Crankcase (block), Cylinder Head, Crankcase Ventilation." It is numbered 01-93101 and captioned "Engine Smokes Blue, Makes Knocking Noises, Runs Unevenly, Valve tappets are noisy with engine at operating temperature." It relates to engines 602.96, 603.96, and 603.971 (produced up to April 1, 1994). This particular bulletin was revised October 1996. It describes the cause of these problems as "Insufficient sealing of cylinder head gasket in area of cylinder head lateral oil channel near cylinder no. 1" and describes the remedy as "Inspect combustion chamber to determine repair, using boroscope if necessary, and replace cylinder head gasket." It cautions that prior to re-installing the cylinder head, there should be a careful inspection of the cylinder head lateral oil channel, the removal of any burrs, and the lightly camfering (sp?) of the edges from the lateral oil channel to prevent splitting of the head gasket sealing edge. Soon thereafter, in December 1995, with a revision dated February 1996, a "Service Tip" was issued, numbered 03T95121, captioned "Limited Availability of Optimized Pistons" for Model 140.134 with engines up to serial number 603.971-12-018446. (I suspect that there were none manufactured thereafter; these were probably sufficient for the balance of the 1994 model year, and the very few distributed as 1995 models.) The service tip advises that "A very limited availability exists of optimized pistons with piston rings for use as remedy against oil consumption complaints." The tip directs the mechanic to "verify related engine components are in correct working order and engine control systems are functioning correctly prior to ordering or installing these special pistons; verify no abnormalities or wear patterns exist with cylinder bores; ensure cylinder bore honing is visible and normal." It goes on to recommend reference to certain specific literature and work instructions, but I do not yet have them. I have also reviewed a Technical Service Bulletin, dated August 1994, that advises of the availability of cylinder sleeves in the event one of these engines is rebuilt. These bulletins speak volumes about our problem. They confirm the legitimacy of our complaints - excess oil consumption, mechanical noise, smoke, uneven running. They demonstrate that enough of these problems had been brought to MB's attention, relatively soon after introduction, that engines had been torn down, specific problems had been found, and solutions (albeit partial) had been proposed. They identify a likely cause - defects in or obstruction of the lateral oil channel. The admonition that cylinders be closely inspected is particularly significant, since it confirms what several of our members have experienced - cylinders that have become out-of-round. =================================== Since last I wrote I have found some data that is of interest, i.e. the number of cars sold in the U.S. with this engine. The numbers are as follows: 1990 350SDL 855 1991 350SD/SDL 3,914 1992 300SD 1,131 1993 300SD 1,005 1994 S350 672 1995 S350 425