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  #1  
Old 06-12-2010, 01:54 PM
okyoureabeast's Avatar
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Excessive carbon in glow plug hole

I recently had my #4 glow plug go out and attempted to replace it. As far as my records show this plug is original from the factory.

Much to my sadness it was stuck in place and I almost rounded the hex bit forcing it out.

I heated the plug with Map gas and PB Blaster (in that order) and still no luck.

Today I drove the car to get it up to operating temp and I left the can of PB Blaster in the freezer. Sure enough soaking the glow plug in cold PB Blaster did the trick and I heard that reassuring crunch that I broke through the carbon.

My problem is though I can just barely see into the hole and it is coated in thick black carbon. I would like to clean the hole out, but I am unsure of what to use to avoid damaging the prechamber (I think this is what it is called).

Could anyone offer advice? I read in an earlier thread that simply getting a small brush in there to scrap off the gunk as well as cranking the engine to blow out the rest is a good way to do it. But the junk is really caked on so I don't want to venture any further without some sound advice.

Thank you for your help and sorry for the short story.

Edit:For those interested, I went ahead and use PB blaster and a pipe cleaner. Seemed to do a good enough job to clean the threads. Eventually I would like to get a reamer, but that will happen later on in life.
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Going back to the original post: "Can you get the vac to blow instead?" No. Vacuums are low pressure so they by nature "suck" and nature abhors them.
1984 380SL

Last edited by okyoureabeast; 06-12-2010 at 03:00 PM.
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  #2  
Old 06-12-2010, 03:00 PM
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They make a Glow Plug Reamer to clean out the Carbon from the Holes and it will not damage anything.
You can buy one, make one or if you are in a hurry there are some alternateive methods to cleaning the hole.

A Factory Made Glow Plug Reamer has a 7mm Reamer on the end of it. So anything that size or smaller ought to be safe.

Also Autolite Glow Plugs are simply awful; after 6 months use I barely got 2 of them out of my Cylinder Head as the Glow Plug Tips had swollen at the end.

Monark Glow Plugs are not as bad but also do not last (they lasted about 1-1/2 years in my car).
Bosch or Beru Glow Plugs are the best with the Bosch ones being the easiest to find and the least expensive of the 2

When you install the new Glow Plugs put some Never-seez type compound on the threads.

Also if you have to remove the rest use something with 6 points on it so you will not round off the Hexes.

Putting the PB Blaster in the Freezer was inovative!

See what you can find below concerning cleaning the Glow Plug Holes.
DIY Repair Links
http://www.peachparts.com/shopforum/diy-links-parts-category/

http://www.peachparts.com/Wikka/DoItYourSelf
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Old 06-12-2010, 03:02 PM
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Thanks Diesell911. I just edited my post when I saw your response. I replaced the glow plug with a Bosch one I got my Napa.

I don't have enough money for a reamer right now sadly, but like I said PB Blaster and a pipe cleaner did a good enough job to clean off the threads.

I have the glow plug installed comfortably in and my indicator light is happily orange now
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Originally Posted by Yak View Post
Going back to the original post: "Can you get the vac to blow instead?" No. Vacuums are low pressure so they by nature "suck" and nature abhors them.
1984 380SL
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Old 06-12-2010, 08:13 PM
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Quote:
Originally Posted by okyoureabeast View Post
Thanks Diesell911. I just edited my post when I saw your response. I replaced the glow plug with a Bosch one I got my Napa.

I don't have enough money for a reamer right now sadly, but like I said PB Blaster and a pipe cleaner did a good enough job to clean off the threads.

I have the glow plug installed comfortably in and my indicator light is happily orange now
There is more to the story. Carbon build up shortens the life of the Glow Plugs. It allows heat to be trasfered into the Cylinder Head insted of heating the Air in the Precombustion Chamber.

I hooked up a Single Glow Plug (the Glow Plug was not in the Engine) to an Amp Meter and found that it maxed out my 60 amp Ampmeter and aver a Second or so as it got hot it settled down to about a steady 16 amps.

What I concluded from this is that if something conducts the heat a way from the Glow Plug it will continue to pull the higher amps. I think that is what shorten the life of the Glow Plugs.

In the Pic between the Red Bars is the area the Carbon builds up in. You can see how Carbon build up that actually contacts both the Glow Plug Tip and the Cylinder Head can conduct heat into the Cylinder Head.
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Excessive carbon in glow plug hole-zy.jpg  
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Old 06-13-2010, 12:08 AM
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How in the world did you get a new plug back in? When mine were tight coming out, they were impossible going back in without reaming the hole. I'm glad I did a search before forcing the plugs back in because they may not have come out the next time. The reamer I bought from Diesel911 works great!

BTW - what does freezing PBB do?
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Old 06-13-2010, 12:57 AM
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Well Adam thats what happens when you run your motor on coal dust & peanut shells or was that coal shells & peanut dust?

You are luck that you didnt leave the end of the GP in the hole !! Best remove and inspect the others if they will come out.

I suspect the cold climate & a number of short runs may contribute to the build up. Some may suggest that using bio-diesel may help keep things clean, I have no proof one way or the other.
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1984 300D 500k miles
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Old 06-13-2010, 03:11 AM
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Quote:
Originally Posted by TchTchr View Post
How in the world did you get a new plug back in? When mine were tight coming out, they were impossible going back in without reaming the hole. I'm glad I did a search before forcing the plugs back in because they may not have come out the next time. The reamer I bought from Diesel911 works great!

BTW - what does freezing PBB do?
I got a small wire brush and sprayed it with PB blaster to clean off the gunk on the threads.

I have no idea actually why it went back in so easily. In fact the little guy went right in without any hesitation.

I ran my engine up to operating temperature and then used the cold PB blaster to cause the metal to slightly shrink back in against the hot engine. I have no idea if this worked, but i got it out so i don't care

@Layback, yeah living in the Northeast sucks. I wish I could go to your land down under with my 300D. There were a ton of mornings where the engine was struggling to start from out of spec valves. I'm guessing this is part of the reason it was hard to get out.
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Originally Posted by Yak View Post
Going back to the original post: "Can you get the vac to blow instead?" No. Vacuums are low pressure so they by nature "suck" and nature abhors them.
1984 380SL
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  #8  
Old 06-13-2010, 03:14 AM
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Quote:
Originally Posted by TchTchr View Post
How in the world did you get a new plug back in? When mine were tight coming out, they were impossible going back in without reaming the hole. I'm glad I did a search before forcing the plugs back in because they may not have come out the next time. The reamer I bought from Diesel911 works great!

BTW - what does freezing PBB do?
Thanks!

What I got from his post was that he got the Engine and Glow Plugs hot and squirted the cold PB Blaster on the Glow Plugs to cool and contract them.
I am not sure if the cold part helped or not but it is well documented on the forum that stuck GPs often come out easier when the Engine is at operating temp.
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