Hello, I have a 1980 300SD that I have a couple questions about. First is the rear defrost - all circuits check out and there is power reaching the plug at the window - strangely there is about 5 mm of green gel like liquid along the entire base of the window. Is it possible for water to get between the layers of glass? Is there anything I can do to restore this? I am hoping for a solution before I have to replace the entire window which involves a lot of $$$! Another strange thing it does is during cold starts it does not want to start at all, it takes ALOT of cranking and will fire on 3-4 cyl while cranking then after it "catches" it will continue to run this way until revved to 2500 RPM. after it is warm even after a day of sitting it will start perfectly, runs smooth and everything is good. Temperatures up here are -40 to 30F in the winter months. Now that I have a block heater it starts as if it were warm, but the thing that concerns me is power is not always available and I don't want to end up stranded. I have replaced all glow plugs, no excessive blow by, diesel antigel, new optima batt, adjusted valves to a bit looser than spec, rebuilt my injectors, adjusted pump timing, and there is very little chain stretch. Only thing I haven't looked at yet is the starter which could be in need of replacement soon. One thing that has me concerned is when I replaced the glowplugs there seemed to be excessive carbon buildup in the GP holes ie when I screwed in the GP's there was resistance and a squeaking sound (not coming from the threads). Is this normal for a diesel engine? Is there a treatment of some sort to remove excessive carbon? any information would be helpful! Thank you - William

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1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4

The rear defroster I don't think I have any suggestions for, but as for the hard starting....have you checked the glow plug relay to make sure it is glowing the plugs long enough? Sometimes they will go bad and not glow for long enough. You should be able to glow for 20 to 30 seconds or so, even after the light may have gone out, and then hear the relay click off. In such extremely cold conditions, I would repeat the glowing 2 or 3 times by turning the key off after hearing the relay cut off and then turn the key back on, before turning the engine over. Minus 40 degrees is pretty extreme, so I wouldn't ever expect instant, warm-weather kind of starting from an older MB under those circumstances.

Hope this helps,
good luck,
Mike

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1979 300 SD
350,000 miles
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1982 300D-gone---sold to a buddy
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1985 300TD
270,000 miles
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1994 E320
not my favorite, but the wife wanted it

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If your SD is equipped with an EGR, you might consider plugging the EGR vacuum (perform search). This should considerably reduce carbon buildup in intake manifold and cylinders. Check GP relay and starter. Motor must reach 100 RPM to start and a weak starter won't get it done, especially in the cold.

There no EGR valves on the W116 SDs. For the carbon in the GP holes, you can use a allen head (6mm) I believe, to scrape that stuff away. What weight oil are you using and is it really getting down to -40 out in Colo.? As for the "firing on 3 or 4 cyl," you may just have bad compression in one of the cylinders. My SD does the same thing. The engine runs like it's miss firing, to use a gasoline term. I can smell diesel coming out the tailpipe. Once the engine is warmed up, she idles smooth. This is simply because the heat from the other cylinders has made it sufficently hot for the low compression cyl. to fire.

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1999 MB SL500 (110,000 mi)
2004 Volvo V70 2.5T (220,000 mi)
2014 Tesla Model S 85 (136,000 mi)
MBCA member

I have found a temporary solution to my problem - I just set my remote starter to start the car every hour when I have no 120V supply available! This will work for the next couple months until I move to a warmer climate!~ kinda a cheesy way around the problem but hey it works for me! as for the glow plug carbon removal I will try this but is it bad to break large chunks of carbon loose into the cylinders? And yes, for a couple of weeks there we were down to at least 40 below up here in breckenridge, that could have been windchill but that's what the thermo read in the morning! Some of our gasoline vehicles wont even start in this but that's just due to neglect. As for the defrost I think ill just go yank a good rear window out of a junkyard car and hopefully it will work, but for 30 bucks I think its worth a shot! - thank you for your replies ~ William

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1983 Mercedes 300SD
1987 Mercedes 300SDL
2001 VW Passat 2.8 AWD
2007 OM642 Jeep WK 4x4