Dear ah-kay,
Just to let you know, I did not blame my son, I could never, thank you for your concern for him, what a decent person you are!
Sincerely, Dana

Typical don't like the message, kill the messenger. I'm sorry you feel that way but the fact remains, your car won't cold start without functioning glow plugs regardless of the ambient temp.
From everything you describe your GP relay is not getting any power and the first thing you should be checking is the GP relay fuse. Keep cranking it like that and you're just dumping more unburnt fuel into the engine oil.
Good luck

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CENSORED due to not family friendly words

Do not quite understand what ah-kay meant about there being no valve adjustment. At least on my 1981 300sd which has about the same engine as you, mine was quite hard to start for a while. Once it fired I had to keep the accelerator down to keep it sped up until it really caught on.

Had the valves adjusted and that never happened again.

OP has an 87 300TD with OM603 engine. This engine has hydraulic lifters that automatically adjust lash. It doesn't require valve adjustment although the lifters have been know to become sticky and cause a ticking sound. That still wouldn't impact compression.

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That is very interesting. I had no idea. I have the 617 engine.

Appreciate the correction.

Thanks. I should have given more details in my first post.

I think the root cause of the no start is electrical, not mechanical. You need a ohmmeter to do the tests on the GP relay.

1) First check the GP fuse inside the box, visual is not enough, measure continuity.
2) remove the big plug, measure the female connectors one by one to chassis for continuity to make sure GP is good.
3) the GP relay works on current balance circuit. It is not perfect. It may turn on the GP light with 1 GP out, sometimes 2, definitely not with 3. Sometimes it is good enough to detect 1 GP out and turns off the light.
4) most of the time, car will start with 1 GP out. In this instance, the car won't start so my guess is that you have more than 1 GP failure. This is my experience.

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Not MBZ nor A/C trained professional but a die-hard DIY and green engineer. Use the info at your own peril. Picked up 2 Infractions because of disagreements. NOW reversed.

W124 Keyless remote, PM for details. http://www.peachparts.com/shopforum/mercedes-used-parts-sale-wanted/334620-fs-w124-chasis-keyless-remote-%2450-shipped.html

1 X 2006 CDI
1 x 87 300SDL
1 x 87 300D
1 x 87 300TDT wagon
1 x 83 300D
1 x 84 190D ( 5 sp ) - All R134 converted + keyless entry.

This is confusing. Do you mean it won't start or won't even grind? "Turning over" can refer to the engine merely cranking, starting or otherwise.

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Te futueo et caballum tuum

1986 300SDL, 362K
1984 300D, 138K

tjts has actually (IMO) given you the best advice. But it seems you're not receptive to it.

My 1991 250TD had starting issues after our snowpocalypse here in Texas in February. I started a thread. I considered and applied the advice given.

http://www.w124performance.com/service/w124CD1/Program/Engine/602_603/15-4000.pdf

My car starts with no problem now.
The advice given was very close to what's been suggested.

We troubleshot the glow plugs and sent it to our local mechanic to do a glow plug overhaul as we have no history on the glow plugs maintenance we figured it couldn't hurt. We do not have our voltmeter with us so the shop is getting this job. We got Titan started with a slight spray of starter fluid, Thanks Diesel911 and drove it to the shop, we figured the money we saved on the tow we could put towards the glow plugs. Thanks to everyone on the forum for all of the help, you are very knowledgeable and we really appreciate you taking your time to help!. I will let you know what the shop says. Sincerely, Dana

When the Glow Plugs are out the carbon needs to be reamed out of the holes or otherwise cleaned. A Mechanic that does not normally work on Mercedes may not have a Glow Plug Reamer. If they have not already done the job you could ask about that.
Without a coupon Harbor Freight store volt/ohm meters are around $7 each.

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84 300D, 82 Volvo 244Gl Diesel