Mercedes Benz problems

Mercedes Benz C250D

My experimentation on my Mercedes Benz C250D started after I was totally and utterly disappointed by the lack of commitment and utter incompetence displayed by a "diesel mechanic" who came highly recommended —by my brother of all people. When I initially bought the C250D she started with difficulty, besides the  injectors were a bit noisy. This wasn't too huge of a problem, because once she started, she would continue to start and drive perfectly normal throughout the day. However, if left overnight, air would somehow seep into the fuel line and the struggle to get the engine started resumed the following morning.  To alleviate this problem, I went and bought a can of "Spanjaard Quick Start" spray for diesel engines; in order to get the engine started for the "first start of the day"... everyday!   It's what I needed to do and was willing to do, to overcome her "morning sickness".

Spanjaards Quich Start Spray

 My dad had a fleet of BMC diesel trucks for several years, so my elder brother who subsequently qualified as a diesel mechanic and I were assignment with the responsibility of fleet maintenance.  As such, I was exposed to truck and car engines and general mechanical repairs for several years, in fact throughout my high school career. During this time I learnt much about the internal combustion petrol engine, indirect injection diesel engines, injector pumps, injectors, spill timing, glow plugs and working of the Otto engine and so much more. 



 However, even though I understood mechanicals fairly well and was pretty much able to do all my own repairs; I disliked always smelling like oil or fuel and detested that my hands and nails always looked dirty, even after I had cleaned them thoroughly. I therefore preferred outsourcing my mechanical work to a qualified mechanic or two. Always thinking that they could or rather would do a better job than me. But boy, was I wrong!

The replacement set of injectors with complete threads

One day, whilst driving  my Mercedes Benz C250D I got the very distinct smell of diesel inside the car —which definitely wasn't normal. So I popped the bonnet; and on further investigation found a pool of diesel inside each of the "Injector wells". The  "Injector well", closest to the firewall was almost completely full whereas the amount of diesel in each of the other four, varied towards a lesser amount. I suspected the leak-off pipes had become brittle or had reached their end of life hence not seating properly. Ostensibly the cause of the air leak that prevented the engine from starting in the morning. 

The injectors that were in the engine. Look at the rightmost injector
- the treads are all damaged with only 4 left as opposed to 7

I really didn't fancy doing the the job myself,  so I consulted by brother  who suggested I should take my Mercedes Benz C250D to this "highly recommended diesel mechanic"  mentioned above. My elder brother was my first choice to do the repair and he could quite easily have repaired it for me. However he had fallen from a scaffold onto protruding bolts whilst working on a ship and permanently injured his spine. He therefore couldn't do any physical work in a bent over position.  For the sake of brevity, I'll call the mechanic Joe.

My initial contact with Joe was somewhat moronic. After I explained about the "morning sickness" and the diesel in the injector wells and the noisy injectors, he gave me a song and dance about having to remove the injectors. Adding that they would have to be serviced, and that they needed to be pressure tested, blah blah blah and the repair cost would be R5500.00. Ending off  that it would take four days. I felt he was a a bit expensive but since Joe didn't know that I knew exactly what needed to be done, I gave him the benefit of the doubt and the go-ahead. Especially considering that he was one of my brother's fellow diesel mechanics. 

Engine with replaced Injectors

I later came to realize, it was the mistake of my mistakes. I might as well have distributed my cash among the street beggars because I would at least have felt that I had gotten more bang for my buck than the flack I received in return from Joe. Four days later, I went to fetch my car and it wasn't ready. His excuse was that Mercedes Benz agents only had 3 copper Injector Heat Shield Washers in stock and that he needed 5, promising that I could get my car back in within a week. I eventually got the car back; and the very next morning the C250D wouldn't start —and in the process I drained the battery. Some  "Spanjaard Quick Start" spray later and a jump start got  the C250D going once again.

Slightly pissed, I took the car back to Joe. Enroute I smelled diesel as before and stopped along the road, only to see that my black plastic rocket/cylinder head cover wasn't replaced and that each of the wells were partially filled with  diesel. I was furious, because in exchange for my payment, at the very least I expected Joe to fix this problem, as well as the no cold starting problem and he did neither. Joe wasn't in that day, so I dealt with his son Abe. He asked me to leave the car with him and that he would relay my complaint to Joe. Three days later I phoned Joe to get a progress report. I was told to collect my car the following day. 

On my arrival and in Joe's absence, Abe told me that the C250D wasn't done because the local Mercedes Agents didn't have the required thickness leak-off pipe in stock and that they needed to fetch the correct thickness from the Mercedes Benz Agency in Somerset West. Three days later I got the car back and it appeared that the leak-off pipes problem was fixed. However the no cold starting problem persisted which I only came to discover the following morning. Once again, I took my back and when I arrived that Joe's workshop they were in the process of moving to a alternative premises. Joe then asked me to give him a few days to settle in and bring my car to the new business premises. 

Two weeks later I took the C250D back and told Joe about the original no cold starting problem which he then said he would fix. Following day I got a call from Joe, saying that he checked every connection and that would have to replace all the transparent pipes at a cost of R1500.00. He assured  me it would solve the problem, so once again I gave him the go ahead. Three days later I got the car back. I then checked on the repairs that were effected, only to discover that the transparent diesel pipes looked like they weren't replaced. So I called Joe to inquire why he had charged me R1500 and didn't replace them. He replied that the transparent pipes were replaced, but with a "good second hand" set. 

I wasn't really unhappy because I was under the impression that I was paying for a new set of pipes. The following morning, the no cold starting problem was back. In fact it was never fixed, so once again I relied on the quick start spray  to get the engine going so that I could take it back to Joe. After haggling over the age of the car and the unknown pressure of the injector pump, Joe suggested that he fit an in-line electrical fuel pump to siphon the diesel from the tank, making it easy for the injector pump to get to the required pressure. All I can say is that I paid another R750.00 for the in-line electrical diesel pump and labour and it didn't solve the problem.

Electric fuel pump that wasn't needed in the first place

Whilst driving the car, I could hear a very high pitch whistle emitting from the engine but couldn't initially identify it, but after seeing the top of the engine was wet with diesel on switch off, I knew it had to come from some where. I then dried the top of the engine, covered it with brown paper, started it  and monitored it.  After a few minutes, I saw the oily marks of the diesel appear through the brown paper above the injector closest to the firewall.  I found that there was a very aerosol-like fine spray squirting from the injector well. On closer inspection, I heard that the high pitch whistle was coming from the injector and realized it was caused by the spray escaping from the cylinder. So looking down the well, I saw the bottom of the injector well covered with a wet black coal-like crusty substance, and knew I had it had a case of "black death".  

This problem commonly occurs with  Mercedes diesel engines when one or more of its injector seals leak. This "black death"  problem can arise when an already used heat shield washer is fitted or inserted upside down (wrong way round) or the injector isn't sufficiently torqued or the injector seat is damaged. As a result, uncombusted diesel and exhaust gases escape past the injector seal, or rather forced out of the cylinder by exhaust compression. This forms a black coal-like hard to remove crust in the injector wells , which will only get worse if not remedied. Installing heat shield washers upside down can damage the injector seat causing it to leak. The only way to correct this problem is to ream out the injector port with an injector seat cutter, insert a new heat shied washer the correct way and torque it to recommended tension.

The 5 heat shields and their used counterparts- correct way up

The 5 heat shields and their used counterparts- wrong way up.

This revelation required me to take the car back to Joe because they had removed the injectors and refitted them. By implication, this was plain bad workmanship. A week later I got my Mercedes Benz C250D back. There was no evidence of "black death" but  two weeks later it returned. By that time I just had enough of Joe because he had my car for a total of 84 days and my C250D was now in a worse condition than when I initially took it to him. I then decided to take my  car to another mechanic who was willing and eager to fix the problem but when I related my woes and told him about my misfortune with Joe, he was hesitant. Apparently he knew Joe fairly well and said they often loan one another's specialized tools, then added he doesn't have the specific spanner for my injector and therefore cannot do the job.

I always knew that if you want something done properly then it best to do it yourself. So that's exactly what I decided to do. I went online, found the requisite injector spanner and ordered it on e-bay, and it was delivered within 40 days. It is described as  1/2" drive, 22mm Diesel Injector Socket Tool For Mercedes Benz OM604 OM605 OM606 ... 1993–1995 W202 C 250 D. 

Assembled engine with replacement injectors.

Within two days, I had the injectors out and replaced them with another set, taken from a complete C250D engine I subsequently bought. It didn't take me long to identify the air-leak that initially caused the morning sickness. I turned out to be a hairline crack in the diesel pre-heater so  swoped it with the pre-heater from the other engine. Now that the fault that plagued me all the time was fixed, I discovered Joe and Abe left me with a new one. They had stripped the tread of the injector closes to the firewall because after I replaced the injectors the high pitch whistle was back. 

Mercedes Benz W203 starter problem

Mercedes Benz W203 starter problem

About 2 months ago, my Mercedes Benz W203 C180K Kompressor's starter motor started slipping when attempting to turn-over  the engine. On average the bendix drive slipped twice for every three tries. Then it progressively got worst, requiring several more attempts before it would finally engage.  My wife was at her tethered end and refused to drive the car unless I fix it. So I planed to do so the upcoming weekend, encouraging her to use the car until then.  

However, as fate would have it, I was forced to fix it much sooner than I anticipated. My wife drove into a Fish Hoek garage for fuel and when the attendant was done, she started the car but nothing happened, the starter didn't turn over, it was silent,  not even a click. After a few more attempts she gave up and phoned me to relate the above mentioned problem, so I grabbed some tools and jetted to her rescue. 

On arrival, I checked that the starter fuse was OK and  I knocked the starter relay with a screwdriver handle a few times, but without success. Then I asked her to turn the key, while I knocked the starter with a ball pane hammer a few times, but to no avail. It started to get dark so I phoned for a roll-back and had to car taken home. The following morning I started my diagnoses. 

Mercedes Benz W203 C180k SAM with its
water proof cover removed.

I suspected that the starter was faulty but wasn't willing to remove it, not until I made sure it wasn't anything else that caused the same symptoms.  So I removed the SAM cover and once again systematically checked all the fuses with a multi-meter. I even switched on the ignition and checked for voltage on either side of every fuse just to make certain I didn't get an ohms reading through some other circuit previously. It all seemed fine, all the fuses were OK. 

Next I pulled out relay the S - starter relay, removed its cover to inspect its contact to see if it wasn't burnt and checked its solenoid for continuity. It seemed fine, but I wasn't convinced that the relay per se was OK. Now since a relay is a electro-mechanical active device I needed to test it, to see if it performs as it should. A relay is just a remote switch, implying in order for it to switch, it must be remotely controlled by a voltage originating from another switch contact. In our case, when the ignition switch is turned on, it sends power to the the relay solenoid which then activates the relay.

Mercedes Benz W203 C180k Starter Relay with the
 diagram clearly visible on its cover

The diagram on the relay cover, shows where each of the terminals  connects to, but it doesn't follow international relay convention. On the diagram, the terminals are marked as 1 and 2, 3 and 5, with 3 and 5 being the physical switch, 1 and 2 being the solenoid winding. In the above image,  the pin marked 3 would normally be marked as 87 and the pin marked 5 would normally be marked as 30. Have a look at this relay. 

These pins carry the load which is normally Open-Circuit and only closes when its solenoid winding is energized.  The pin marked as 1 would normally be marked 85 and pin marked 2 would be normally marked as 86. Be that as it may, this relay was probably an after market component, even though it sports the Mercedes Benz emblem on the other side. It worked fine even though it was a fake Mercedes Benz relay.

Mercedes Benz W203 C180k starter solenoid continuity test

With my multi-meter switched to ohms, I checked the solenoid winding and as you can see, it measures .3 of an ohm. The solenoid winding is connected to the multi-meter with 2 dog clips that is connected to the multi-meter's leads. In the image below, I'm applying 12 volts to the relay solenoid with the dog clips connected to the switch and the relay activated as it should. 

Mercedes Benz W203 C180k starter relay solenoid switching test

Mercedes Benz W203 C180k SAM with the Starter relay 
and fuse in the top left hand corner

Satisfied that the fuse is OK and that the relay was working as it should, I needed to bypass the relay, thinking that the Ignition switch may not be sending the required voltage. So looking at the image below, the relay in the far left corner, sitting behind the red fuse is the starter relay, which I reinserted. Mercedes Benz agents are fully aware of the starting problems Mercedes Benz owners are experiencing with the cars. 

So they've even published a bulletin, recommending that when their techs receive a job card with Engine Not Starting / Starter Fuse Malfunctioning, that the 15A fuse F52 which may be blown on the Signal Acquisition and Actuation Module (SAM) should be ungraded to a 20A. 

This issue affects the following sub-types of the Mercedes Benz W203 chassis:- 203.040 / 203.052 / 203.054 / 203.056 / 203.061 / 203.064 / 203.065 / 203.076 / 203.081 / 203.084 / 203.087 / 203.092 / 203.261 / 203.264 / 203.281 / 203.284 / 203.740 / 203.747 / 203.764. Essentially Mercedes Benz W203 C-Class C180, C200, C230, C240, C280 and C320 year models ranging between 2000- 2008. 

Mercedes Benz W203 C180k starter relay removed
and replaced by a link between its load contacts

As can be seen in the above , I subsequently replaced the starter relay with a thick black jumper lead, now occupying the place of the stater relay connected to pins 3 and 5 of the removed relay. With this thick black jumper in place, the starter should turn if its not faulty when I turn the ignition key. Unfortunately nothing happened, though proving decisively that the starter was indeed faulty. 

So I got out the tools and removed the starter after I had checked that the started solenoid voltage was present when the ignition was turned. Due of limited space between the bell housing and the car body, I needed to joint 2 long extensions together with a swivel adapter in between for flexibility. Then added a second swivel adapter between the extension and the 15mm spline socket, all attached to a power bar to remove the two long starter bolts.

Faulty Mercedes Benz W203 C180k starter with solenoid screws undone

After removing the starter, and cleaning the grime from it, I struggled to undo the starter solenoid screws and ended up damaging the screw heads. I then resorted to an impact-driver but to no avail because the screw heads were just too damaged. I  painstakingly hammered each screw with a cold chisel and  eventually I got them loose. Luckily I had another starter from which I could salvage three screws that were in perfect nick.

Mercedes Benz W203 C180k starter completely dismantled.

Opening up the starter was quick and easy, only to reveal that two of the four brushes were completely worn down to its very last, and two dangling copper wire braids that were attached to brush graphite at some time in the not so distant past. The brush module was clogged with grime and to make any sense of what I was dealing with, I had to clean it up.  

The faulty Mercedes Benz W203 C180k brush panel fouled with grime

So out of curiosity, I cleaned up the debris to reveal the following. One of the springs were broken and slightly worn away. A small piece of one  of the brushes survived along with the brush holders, non of which were usable because the new brush panel comes as a complete unit. The fact that the brushes didn't make contact with the armature any longer was the real reason why the starter wouldn't turn-over. Besides, it very miraculously and very surprisingly continued working until its brushes were beyond end of life. Lucky me...

Disposable parts of brush panel

Brush panel backing plate with braid wires still attached

As can be seen in the image above, the brush panel still has two bits of braided wire that was once attached to brushes. Using a stick I further removed the rest of the grime out of the field coils and wiped it down with a solvent in order to restore it to its former glory. 

The Mercedes Benz W203 C180k field coils in the process of being cleaned.

Prior to this starter problem. I had the Oil Cooler replaced which you can read about in the previous blog page. I suspected that oil had dripped down onto the starter, seeped inside and mixed with the worn-off brush particles to form a sludge. Considering that the Oil cooler sits directly above the starter, there was no other reason for the thick oil-like substance that's visible on the stick above, to be inside the starter. 

The Mercedes Benz W203 C180k field coils after its been cleaned.

With the field coils all cleaned and shiny. I started the repair process by buying a new bendix and a new brush panel kit. The part numbers are as follows: Bosch part number 1006 209 801 and Bosch part number 1004 336 526 respectively. It is also clearly visible on the respective packaging.

The new Mercedes Benz C Class W203 bendix

The new Mercedes Benz W203 brush panel 
with the brushes side up.

The back side of the new 
Mercedes Benz W203 brush panel

The old bendix drive had virtually no friction or rather resistance on rotation, so comparatively it was easy to determine that it was definitely faulty. Besides it is the only item inside the starter motor that can produce the slipping sound. Surprisingly, as can be seen in the pic below, the teeth of the bendix  where it meshes with the teeth of the flywheel weren't worn off at all. 

The new Mercedes Benz W203 bendix on the shaft and the old and worn 
Mercedes Benz W203 bendix below.

Fortunately the armature wasn't damaged in the process, and a few light strokes with a piece of  emery cloth rendered the brush contacts shiny and smooth. There was no visible wear on the armature shaft either, because the bronze bushes were impregnated with oil which dripped into the starter. 

The Mercedes Benz W203 armature before cleaning 
and the solenoid after testing it for continuity.

Reassembling the starter was quick and easy because everything just slipped together. The bendix slid onto the shaft and the fulcrum slid into its guide, all of which slid into the field coils without any fuss or bother. 

The Mercedes Benz W203 bendix assembly with the fulcrum 
balancing on top of it.

Getting the new brush panel onto the armature was simple because of the disposable plastic  guide that keeps the brushes the exact distance from the armature contacts to just slip it into place, as can be seen below.

The new Mercedes Benz W203 brush panel seated onto the armature.

The disposable plastic guide just about to pop out of place

With the rear cover in place, it was time to fit the grease cover.

Mercedes Benz W203 Bendix drive assembly ready for assembly

Mercedes Benz W203 Bendix drive inserted into casing and ready for assembly

Mercedes Benz W203 starter assembled 
but in the process I chipped a piece off the casing.

Assembly complete with screws torque to correct tension

Starter fully assembled ready for testing

Starter fully assembled Mercedes Benz W203 starter ready for testing.

Earth jumper cable connected on the body of the Mercedes Benz W203 
starter  and 12V connected on the solenoid supply side.

As can be seen the battery voltage sits at 12.27 Volts prior to testing

Multi-meter connected to battery supply shows that the voltage dipped
just under  11 volts when cranked.  As can be seen the green dog clip is
 connected to the solenoid and I'm touching the other end to the  the 12V supply,

Mercedes Benz W203 starter was fitted and car started first time

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W203 doesn't start, does not crank. / Mercedes won't start. / Merc W203 starting Problem. / How to remove starter motor of c180 kompressor W203./ Mercedes benz starter motor problems. / Fixing A Mercedes-Benz That Won't Start./ Engine won't crank over with the starter. / Why is My Mercedes having a starting problem? / Mercedes Benz starter motor problems. / Mercedes Benz starter problems. / W203 mercedes benz won't start. / Mercedes Benz W203

MERCEDES BENZ W203 C180K OVERHEATING

Mercedes Benz W203 C180 Kompressor

My wife is a merchandising agent and needed a larger car or at least one with larger boot space in which to cart her display boards; so I bought her a 2004 Mercedes Benz  W203 C180 Kompressor Estate with 180 000 km on the clock.   It was exactly what she needed, inconspicuous gun metal grey with light grey seats that folded down giving her the space she desired. Cosmetically, the car was in pretty decent condition and according to the seller, he had just forked out a ton of cash for parts and labour. He had replaced the timing chain and the A and E sprockets and even gave me the invoices for that job, but was selling the car, As Is. It was fitted with new tyres, the rims had been re-epoxyed and the interior was recently valeted. 

Overheating 

My wife took the car for a test drive and was impressed by its performance, however the very next day we started having problems. So much for buying a car in condition "As Is". The car overheated, steam blowing from beneath the bonnet and leaving large pools of water behind. After I diagnosed the problem, it was just a sticking thermostat that needed replacement. The thermostat housing is positioned below the timing chain sprockets and I surmised that the mechanic who fitted it, tightened it at an angle and in the process bent its plunger. Obviously thinking the worse, its owner probably wasn't prepared to pour money into this beast, so he sold it off at a bargain price. 

A week later my wife complained that she had to add water daily since the  the "add fluid" signal triggered repeatedly an alarmed her.  I knew there had to be a water leak but couldn't find it, until she phoned me to tell me that the garage attendant said that there was oil in the water. On later inspection, I found a layer of oil in the water expansion tank, but when I opened the oil cap, there was no white sludge in the oil. I was certain it wasn't the head gasket that blew and I suspected that the Oil Cooler had rotted internally. My thinking was that the oil pressure is much higher than the water pressure, and oil could therefore seep into the water but not the other way round. Besides, A and E sprockets, timing chain and Oil Coolers are common problems associated with the M271 engine.

The oil cooler, part no A2711880001 rots inside allowing the
higher oil pressure to seep into the water.

Oil Cooler

The Oil Cooler has four holes in it. An inlet and outlet for water and an inlet and outlet for the oil. Each running through seperate and intermingled veins inside the Oil Cooler. As such the water manages to cools down the oil. However it the veins corrode and the separation is breached, the oil finds it way into the water expansion tank. The Oil Cooler sits in such an obscure place on the W203,  that it would probably be easier to replace a cylinder head gasket than replace the Oil Cooler. To save myself the frustration, I took it to my mechanic who confirmed my suspicions and subsequently replaced it, but two weeks later. Apparently the Mercedes Benz agents didn't have any in stock because it sells out very quickly, hence we just had to wait. We hardly got the car back and the boiling continued. My thinking was that the Oil Cooler was the cause of the problem but it wasn't. It was probably also the reason the previous owner sold the car, knowing that the oil was mixing with the water, drained it and replaced it with clean water before flogging it to me. 

W203 expansion tank 

After a thorough diagnosis, I found that the expansion tank outlet under the hose clamp was leaking and that it had been Pratley Puttied by someone. So I bought a new tank and replaced it, thinking it would solve the problem but it didn't. After replacing the expansion bottle cap which is sold as a separate item, the problem was  finally solved. Ever since the car has been going really well for about four months. Occasionally the started slipped  when attempting to start the engine and I knew it was just a matter of time  before the bendix would have to be replaced.  

Continued here!
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W203 doesn't start, does not crank. / Mercedes won't start. / Merc W203 starting Problem. / How to remove starter motor of C180 kompressor W203./ Mercedes benz starter motor problems. / Fixing A Mercedes-Benz That Won't Start./ Engine won't crank over with the starter. / Why is My Mercedes having a starting problem? / Mercedes Benz starter motor problems. / Mercedes Benz starter problems. / W203 mercedes benz won't start. / Mercedes Benz W203 chassis:- 203.040 / 203.052 / 203.054 / 203.056 / 203.061 / 203.064 / 203.065 / 203.076 / 203.081 / 203.084 / 203.087 / 203.092 / 203.261 / 203.264 / 203.281 / 203.284 / 203.740 / 203.747 / 203.764. Essentially Mercedes Benz W203 C-Class C180, C200, C230, C240, C280 and C320 year models ranging from 2000- 2008.

MERCEDES BENZ STARTING PROBLEM

MERCEDES BENZ STARTING PROBLEM

The Mercedes-Benz C-Class 250 TD (W202) sedan  and the T-model station wagon with the OM605 5-cylinder engine manufactured from 1992-2000 is probably one of the rearest cars in the Mercedes stable. The W202 model C-Class cars were the first to display the modern Mercedes-Benz  naming scheme, where the badged numbers are followed by letters. For example C250 instead of 230E or 280SE or190E, etc.

The W202 shape with the "facelift" replaced the original W201 190 series sedan; "Baby Benz" (1982-1993)  though less than 2 million W202 models were produced since its inception. The W202 shape came in a number of engine capacities, with slight difference in their bodies. Below is a list of some of the W202's manufactured between 1992 and 2000 with engines ranging from the 4 cylinders in-line (straight)  engines of the C180 to the V8 of the C55T AMG .

Mercedes-Benz OM605.910 engine

The Mercedes Benz W202 range of Petrol  & Diesel Cars

C180 and the C180T,  
C200 Kompressor, C200 Diesel, C200T Diesel, C200 CDI  
C220, C220T, C220 Diesel, C220 Diesel T,
C230, C230 Kompressor, C230T, C230T Kompressor, 
C240 and the C240T, 
C250D and the C250 Turbodiesel 
C280, C280 (V6) and the C280T (V6) , 
C36 AMG. 
C43 AMG and the C43T AMG 
C55 AMG and the C55T AMG 

However, the only  engine of interest at this point in time is :- Mercedes-Benz C250D 83kw normally aspirated in-line (straight) diesel engine (OM 605.910). Only 44,801  cars with the aforementioned engine were manufactured between 1992-1996. The Mercedes Benz C250D 110kw Turbodiesel  engine (OM 605.960) is essentially the same engine but sports an added turbo charger. Again only 59,772 were manufactured between 1995-2000. These two engines are in fact the little brothers of the Steyr-Daimler-Puch tractor (OM 606.964) 3.0 litre engine which is essentially the four valve per cylinder successor of the OM617 two valve per cylinder engine. An engine proven  to  exceed  500 000 to 1 million miles before needing an overhaul and is therefore considered to be one of the most reliable engines ever produced.

Mercedes-Benz OM605.910 dual overhead cam engine with intake manifold,
valve cover and high pressure injector pipes removed 

This extremely successful Mercedes-Benz OM606  3.0 litre engine, is an inline-six cylinder double overhead camshaft (DOHC) diesel engine sporting indirect injection. Likewise the Mercedes-Benz OM605.910  / OM605.960 is the 2.5 litre inline-five cylinder double overhead camshaft (DOHC) diesel engine also sporting indirect injection. These engines are relatively noisy because of indirect diesel injection yet they are strong and powerful,  with low fuel consumption and excellent reliability. 

Mercedes-Benz C250D diesel fuel seals

Diesel engines have two peculiarities, they are sometimes difficult to start and sometimes difficult to switch off. Both of which are relatively easy to repair. Often times starting difficulty is associated with the glow plugs. Glow plugs are essentially 12V heater elements fitted to the combustion chamber that heats up, to ignite the first sprays of diesel from the injectors. A continuity test between the the engine block (earth) and the glow plug connector node will determine whether any of them are open circuit. Continuity or a low resistance reading (typically between .5 and 4 Ohms) doesn't necessarily mean the glow plug is operational. 

The best test is to remove the glow plug, dip the heater tip into a bit of water and connect 12V to the glow plug using jumper leads. Earth/negative terminal to the body of glow plug and Live/Positive to the connector node. The water will turn into steam even before the glow plug tip glows red. That's sufficient to know that the glow plug is functional. Be careful not to touch the tip, it will burn your fingerprints off . I've encountered glow plugs with good continuity (1.5 ohms) but when I connected the 12V  across them, using  jumper leads, all I got was a spark on connection and no steam nor heat, it was  dead glow plug even though  it had continuity. Also bear in mind, there are three things needed to start a diesel engine.

1) Compression - The air in the combustion chambers is placed under such enormous pressure that it's hot enough to ignite the diesel spay spontaneously.

2) Diesel - Supplied under pressure (115 bar) must be devoid of air bubbles. Bleed off air before attemtping to start the engine.

3) Electricity (12V) - Needed to power the glow plugs , the electronic shutoff valve and the diesel pump. When engine is hot, glow plugs aren't needed any longer since the engine is fitted with a diesel pre-heater.

So if any one of the above three is missing, the car won't start. The assumption is that if the car starts everyday and displays sufficient torque, the likelihood when it doesn't start wouldn't be compression  associated. Diesel engine compression range between between 275 psi and 495 psi,  with typical compression ratios of between 15:1 and 23:1. When diesel is sprayed into the combustion chambers through the diesel injector nozzles - the moment the air in the chambers are under great pressure - it's normally hot enough to ignite the diesel spontaneously. However, when compression is suspect, an average pressure of 300 psi is good but no cylinder should vary by more than 10 percent.  Anything greater than 50 psi difference between cylinders will also cause starting problems,  poor acceleration, diesel knock, excessive smoke and can lead to rough idling. 

The part numbers for the 6 hoses are 605 070 12 32, 605 070 10 32,
605 070 15 32, 605 070 07 32, 605 070 08 32, 605 070 14 32,

Another problem with this engine are the clear diesel pipes or rather its seals that leak,  allowing air into the fuel line causing the injector pump pressure to drop substantially. When this happens, the battery can often be drained before the engine is cranked long enough to buildup 115 bars of pressure. However, a squirt of Spanjaard Quick Start spray into the intake manifold should get her idling. But, this screams very loudly that there is some sort of problem that needs to be solved sooner than later.

The part numbers for the 6 hoses are 605 070 12 32, 605 070 10 32,
605 070 15 32, 605 070 07 32, 605 070 08 32, 605 070 14 32,

So remove intake manifold, check the  glow plugs, test  them as mentioned above. Next remove the six clear fuel lines and check the "O" rings for leaks and if they are wet with diesel  replace them with those  supplied by Mercedes-Benz. I've tried various "O" rings from several sources and believe me, they don't work and always leak. The ones from Mercedes-Benz agents are silicon rubber based, manufactured with a tight tolerance.  Next check the shut off valve for leaks. The "O" ring behind the shut off valve tends to perish because it endures the heat transferred from the engine block to the injector pump. Do yourself a favour and get the right one. It will save you time and money.

Clear diesel pipe attached to clogged filter

Fuel filter cleaned out 

The grime that clogged the fuel line.

Also check the hoses clamps on the fuel lines between the non return  fuel cut off valve and the  fuel heater/exchanger. I had a very minute,  hardly visable, crack in my car's heat exchanger.  Early Mercedes-Benz W202, were fitted with biodegradable wiring harnesses.  Unfortunately, this biodegradable insulation deteriorated much quicker than it was anticipated due to moisture and heat in the engine compartment. I had to replace mine because there was more visible copper than insulation on the wires. So check the harness between the shut off solenoid valve and the ECU for cracks and brittleness; replace if necessary.  Also clean the small fuel filter, its bound to have dirt in it. 

Perished  wiring harness and fuel hoses that needs replacement.

And lastly, check the shut off valve at its ends for leaks, if it does leak, replace the seals. The seals are held in by four pins that needs to be pushed out in order to get to the seals. Unfortunately Mercedes Benz agents do not supply these seals separately. One has to purchase the complete shutoff valve at some ridiculous price which I just couldn't justify. The ones I used were roughly 31.88mm in diameter, slightly larger than the ones that came out. Putting them back was an itch with a B. As can be seen I used a G clamp that worked wonderfully indeed.

Shutoff valve with the seals removed

O rings slightly bigger than the ones that were removed.

 The only way I was going to get the end caps back in place was with a clamp.

Shutoff valve closed with "O" ring on nozzle that fits into diesel pump.