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'81 240d
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229 Posts
Discussion Starter #1
So now that spring is here, I'm finally getting around to fixing up my glow system. Perhaps my priorities are not fully straight :banghead:, but hey, better late than never.
Anyways, my car was starting really crappy over the winter. I live in NC, so it never really even got properly cold, but starting it at 40 Fahrenheit was a chore (I'd have to glow 5 or more times, and after that crank it for a while), and if it was anywhere near freezing my the engine would just give me a wheezy laughing-at. I tested my plugs over the weekend and found that I had 1 faulty one, and replaced it and the other 2 factory originals for good measure.

Now of course it's warm out so I can't really tell how much that's improved things, so one question is, how big of a difference does 1 plug make when starting in cold weather?

Also, I wonder if my car doesn't preglow as long as it should. The glow light turns on for 4 seconds, then turns off. If I leave the key in the glow position, do the plugs stay hot?, or do they turn off when the light is off? Should my light be staying on longer than that? If so, would that be a problem with the relay?

Also, does anyone know of a way to test the engine block heater? My manual doesn't mention it and when I plug it in my engine never seems to get much benefit.

Also, just out of curiosity: the MB glow plugs I pulled out of my engine were tapered off towards the end of the pencil, making them bullet-shaped-- but the autolite plugs I replaced them with were cylinders. Do they get worn down over time, or are they made differently now?

And one final question: Can someone describe the circuit the glow plugs are on to me? I see single parallel wires connecting to each plug, and then one common wire going out of the engine block, but I can't figure out how they are connected.

Thanks!:)
 

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1984 €uro 300D NA
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758 Posts
One bad glow did make a difference last winter. Did you ream out the crusted carbon prior to replacement? The GP light is an indicator of a good GP system. It should go out in a few seconds, but as I see it, going out means you can now crank the car but I believe the GPs still energize for a few seconds longer. Maybe up to 15-30 seconds. In the past when really cold I wait a few seconds AFTER the GP light goes out to crank. This added time does help in very cold starting. The block heater if working correctly makes a "woosh" sound. With my car off I can hear the faint noise. It's the exact sound an electric water heater makes once you plug it in. AutoLite glow plugs are junk and problematic. Get the Bosch brand. Each manufacturer has a slightly different pencil tip design which is OK to mix and match except the AutoLites will probably fail first.
 

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1979 280CE
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6,118 Posts
Do you have the old style loop glowplugs? If you do then 1 glowplug will make all the difference. If one plug is bad then none of them will work.

If you have 28 year old glowplugs in that car then replace them all.
 

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'81 240d
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229 Posts
Discussion Starter #4
My glow plugs are parallel wired, so one bad one shouldn't have ruined the rest. My car was carrying 3 MB originals and 1 Bosch-- I replaced all the originals and left the Bosch in.

Thanks for letting me know about the preglow light! I had been turning the key back and forth a few times to keep the light on, but I guess I should just sit and wait. With my hood popped, I can hear the relay 'click' a while after the light goes out, that's probably what I should think about when wondering how long the glow plugs energize the cylinders.

What tool would you use to clean off the carbon deposits? Where should I expect to find them? Should I be nervous about knocking that crud into the engine? I just relish the opportunity to take those plugs back out :crybaby2: but at least they shouldn't be gunked in as badly this time.

Nothing seems to happen when I plug my engine heater in-- does anyone know a common problem that might have done it in? My manual doesn't even mention it.
 

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1979 280CE
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6,118 Posts
have you adjusted your valve within the past one year?
 

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'81 240d
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229 Posts
Discussion Starter #6
I have not adjusted my valves yet. It's on my to-do list for the next few weeks-- although I confess that I'm a complete newbie and if I haven't worked on something yet I probably don't know anything about it. How would that affect starting?
 

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1982 Mercedes 300D Turbo Diesel
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141 Posts
be patient as reaming the glow plugs might take a while and don't worry about what gets knocked in as it will be expelled out the exhaust. you are correct in that the relay clicks when it goes off. about 20-30 seconds is how long my lasts before i hear the click.
 

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1984 €uro 300D NA
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758 Posts
.
What tool would you use to clean off the carbon deposits? Where should I expect to find them? Should I be nervous about knocking that crud into the engine? I just relish the opportunity to take those plugs back out :crybaby2: but at least they shouldn't be gunked in as badly this time.
Another over priced item from mercede$$ource but the reaming tool is awesome at properly re-boring the hole as it removes the carbon.
 

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2013 MINI Copper S Clubman, '84 300CD-weekend car
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10,152 Posts
Another over priced item from mercede$$ource but the reaming tool is awesome at properly re-boring the hole as it removes the carbon.
Over priced like everything else from there.
I have one tho, you're welcome to use it, PM me if interested.
 

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1982 Mercedes 300D Turbo Diesel
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141 Posts
i also own the tool and could loan it out. let me know if you are interested. i'd probably send it via snail mail so might take a few days to get there. PM me and we can make arrangements.
 
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