Hi all
I have a question to the respectable members of this form.
I recently bought an old 1967 200D diesel OM621 diesel , about a year ago . to make long story short the engine is supposed to be about 60K miles (I can't verify this but prev. owner claims the car been parked in his neighbor's backyard for more than 20 years ).
I've managed to drive my 200D for about 7000 miles so far,once she started she runs good , smooth idle, does her 80 miles per hour, 30-32 miles per gallon ,45 psi oil pressure, compression test approx. 3 month ago seems like all 4 cylinders give more than 300 psi ..
my question regarding cold start; seems like it is quite hard to start the engine up sometimes the start is relatively easy , just 2-3 cranks after long preheat , but sometimes it doesn't want to start at all and only after long cranking with starting fluid eventually and a lot of frustration it starts... (now she is doesn't want to start without starting fluid at all)
for example I could start this car during the day without problem now lets say she is parked for 2-3 days so it is almost impossible to start after that. but the hot engine starts up right away...
seems I've checked that ever I could , all the lines , changed filters. tried to run her from the small fuel container in the engine compartment instead of fuel tank, valves adjusted, serial glow plugs changed 4 month ago , no any difference in cold start whatsoever
every new day is a big puzzle: cold start or not to start at all.
I realize this is a 40 y.o car .. I don't mind working on such a dinosaur diesel so any advice would be greatly appreciated
Thanks for all the inputs

I'm going to guess that you have a small leak that is allowing air to get into the fuel system. I know you already checked the fuel lines, but it's probably a really small leak that you missed. Since you don't have fuel leaking out, I would further speculate that the leak is on the suction side. Since you've already tried running it from a container instead of the fuel tank, I'd concentrate my inspection on the last bit of line going to the injector pump, and also check for a leak on or in the pump itself. It may be helpful to pressurize the fuel system in order to help find the leak.

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Whoever said there's nothing more expensive than a cheap Mercedes never had a cheap Jaguar.

83 300D Turbo with manual conversion, early W126 vented front rotors and H4 headlights 400,xxx miles
08 Suzuki GSX-R600 M4 Slip-on 22,xxx miles
88 Jaguar XJS V12 94,xxx miles. Work in progress.

If the 621 is like the 616 and 617 all of the lines after the lift pump should be pressurized. I would try changing all of the fuel lines. They could probably use it anyway. Those old braided hoses are almost impossible to find pinholes in.

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1979 240D- 316K miles - VGT Turbo, Intercooler, Stick Shift, Many Other Mods - Daily Driver

1982 300SD - 232K miles - Wife's Daily Driver

1986 560SL - Wife's red speed machine

Those old 621's could be tough to start even when they were new.

I think the biggest problem is the starter does not turn it over fast enough.

I am 90% sure that a starter from a 300D turbo would fit on there. Perhaps someone on the vintage forum could confirm or deny that.

Keep an eye on your compression. From 68 on, there was some bad metal in the engines for a few years. Cylinders would out egg shaped. I think most 67's were OK, but I don't know exactly when that problem started.

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Palangi

2004 C240 Wagon 203.261 Baby Benz
2008 ML320 CDI Highway Cruiser
2006 Toyota Prius, Saving the Planet @ 48 mpg
2000 F-150, Destroying the Planet @ 20 mpg



TRUMP .......... WHITEHOUSE
HILLARY .........JAILHOUSE
BERNIE .......... NUTHOUSE
0BAMA .......... OUTHOUSE

After the car has been sitting for a few days, and you know it will be hard to start, try bleeding the fuel system. Crack the bleeders on the fuel filter and on the injection pump and prime the system before you start it up. Mine had the same problem, and it eliminated other problems from the equation. The original engine in my '67 was rubbish. It was severely worn out at a fairly low mileage. Everything inside it was pooched. It may have been due to a lack of maintence, but I've also heard of bunk engines of this vintage.

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1967 200D FINTAIL (in service)- 86K
1983 VOLVO 244 DL (daily driver)- 300K
1988 VOLVO 244 DL (ice racer) - 345K

hi everybody ,
thanks to all for the input. I've bought the new fast glow plugs approx. a week ago, bosch 0250201010 , had some time to test them. Now the engine starts much better , however some cranking is still needed. I wired these GP to the same point after resistor on the firewall as the old GPs , just without ground on the GP #1. Seller indicated that these plugs need 9V DC. I've checked the voltage after the resistor and it is about 6V (as far as I understand for the old serial plugs). I left everything as it is for now; on top of that I do not have the time relay , I just utilized the existing pull knob.
so my guestions:
1. what is the correct voltage for these fast GPs ? I have 10V before the resistor so I can wire the GP without it ...
2. do I really need a time relay ? lets say if I keep the knob pulled 30-40 secs. or more can I damage these new pencil type GPs ?
thanks,
Ruslan

hi again , some updates. I've installed the fast glow plugs and hooked them up without firewall resistor (10V feed currency), It seems like the car began to start much better now ... but still sometimes I just can't start her up . this weekend was relatively cold, 39F at night, so I had no luck to start in the morning.. but this morning temperature was almost the same , ~ 40F , I primed the pump before actual cranking and engine started easy.. this leads me to believe that there is some air leak somewhere ... I've checked all the rubber hoses from filter to IP pump, replaced the fuel hose to primer pump and return, tighten all clamps, replaced prime pump... I've noticed that when I push prime pump it takes several pushes until pump starts to pump fuel ... so my question is what else could be wrong with mechanical prime pump, I've replaced that notorious part but maybe the whole prime pump body ,which bolts on to the IP pump needs to be replaced or maybe the valves inside it leak the air or fuel back to tank? or maybe the partial solution would be to buy a universal electrical pump and install it before prefilter ?
thanks for the replies .

First off, DO NOT USE ether (starting fluid) with glow plugs unless the glow plugs are unhooked. This may cause serious damage to your engine. Ether should only be used as a last resort.

Now, as far as the fast start glow plugs, I don't know if the resistor on the firewall is needed with those. I can tell you that with the original style, bypassing the resistor will cause a glow plug to burn out faster.

There are one-way valves in the inlet and outlet of the delivery pump on the side of the main injection pump that are available seperately. Could be that they are leaking back and causing a lose of pressure in the system. I seriously doubt the delivery pump itself is bad. It is also possible that the main injection pump has internal leakage from normal wear or the injector tips are leaking relieving pressure in the injection lines.

These engines can be very difficult to start when around the freezing mark or lower. Engine block heaters are a big benfit at this point. On diesels, the faster you can get the engine to turn over, the better. If the engine has a lot of wear, it could be low on compression, making it harder to start. You might also try adjusting the valves, as I have heard tight valves can make the engine start harder (I assume due to lose of compression).

Hi,
Instead of the glow plug resistor use a 50A fuse

Fuse A000 545 25 34
Fuse Box A123 540 04 50
Did you replace the 3 metal loops between the plugs with wires?
http://dieselgiant.com/mercedesdieselloopglowplugrepair.htm


I had the same problems and that`s what I did:
---Replaced ALL the rubber fuel lines from engine to tank-easy task,they were 40-y`s old anyway...the small feed line from the tank to the feed line had different diameters on each side and had to be bought from the dealer and was pain to replace...just leave it.)
---Removed and inspected the lift pump.Changed the original hand pump with the new style one,tightened WELL. Checked and cleaned the 2 valves,some rusty particles from the tank,the 2 o-rings were o.k....Removed and checked the relief valve on the inner side of the IP...
---Got rid of the original aluminium primary filter assembly and installed a transparent ordinary Mann ..
---Checked all nuts and bolts on fuel lines,filter,pump...
However,after priming the hand new hand pump(what a difference!) there was still some air in the primary filter...tapped it hard,primed again(all this several times) until no air was visible in the filter.Now even after a month the hand pump is firm...
Before reinstalling the lift pump,rotate the engine by hand in such a way that the IP cam lobe is not in contact with the lift pump plunger for easier tinghtening of the 2 nuts...And change the oil in the IP .Total costs: appr.25$
P.S. You do not need a time relais.Keep things simple.You don`t need the resistor either...Just get the correct gauge wire..And the fuse..

thanks for the info .
yes I've manufactured some new wires for the pencil glow plugs, It seems like it is a good idea to install 50 amps fuse.. I gotta do this . I have installed a new type hand pump as well so I noticed that when I push it I hear some air leaking noises during those pushes .. maybe it is normal ??!! pump is brand new .
Vox_incoognita , you mentioned this relief valve on the inner side of the IP, where is it ??? seems I can't find it. thanks a bunch for the explanation.
P.S the most upsetting thing that non starting engine followed by the drained battery normally happens when you in a rush and really need the car.... my MB may start very well , lets say weeks in a row but on one particular day .. . it is very frustrating in deed .. after that everything back to normal.

Just quick update on my cold start problem. I've followed all the advices on this thread: fast GP , fuse , replaced hoses , cleaned up all valves, new battery wires , some more tinkering . It seems that the my OM621 began to starts much better .. but all over the sudden winter came ... temperature dropped to 26-27 F so I started to experience the same problem again. morning start became a frustration again. so decided to take more serious actions. to make long story short , installed the new timing chain (old one stretched about 4-5 degree ) the camshaft (it came out the old one has pretty much worn lobes) . Now I see the huge improvement in my cold start drill ... engine starts after 4-5 cranks and at least she starts all the time ... so far.. (cant say anything yet about colder temperatures )
b.t.w. does anyone knows what is average life span of OM621 camshaft ? 60-70K more/ less ?
thanks ,
Ruslan