Glow Plug Threads in Aluminum Head

[dkr]

Disclaimer: this is for a VW Tdi, but the same concept as Mercedes. I tried to have my head rebuilt and was told that three of the four glow plug holes were missing threads and it was caused by keeping the glow plugs in for too long. I have heard similar horror stories about replacing glow plugs in Mercedes with aluminum heads. Is there some type of preventative maintenance for this? I have a brand new head I will be installing. I was thinking about putting some grease on the threads, but I wonder what will happen as it melts up each time I turn the car on and solidifies after the engine stops. Would it be better to pull out and put back in the glow plugs every few years?

Thanks,

Dkr.

[Diseasel300]

You can use metallic anti-seize like you'd use on spark plugs. Same concept. Most likely what happened is the GP's were replaced and whoever installed the new ones did it dry or over-torqued them.

[cmac2012]

Whoa, that gives me a wee bit of pause. I've only had my 300SDL about 2 months, I like it, would be nice to get one or two hundred K out of it. The glow plug light only comes on now and then. It starts but is often a tad rough, at least until I take it up to 2,000 for a few seconds. Leads me to think some unknown number of plugs aren't working. I don't know any of the maintenance history. I suspect I should try to put in new plugs soon. I knew there might be difficulty, first I've heard of thread damage for being in too long. But it makes sense.

[Diseasel300]

I had the same issues with my SDL when I got it. The glow plugs came right out on mine, despite looking like something dredged from the Titanic. Stripped threads on the 603 don't seem as common as some others, especially the 606.

Regarding the Glow plug light only occasionally working: See this thread I did earlier in the year: http://www.peachparts.com/shopforum/diesel-discussion/383193-glow-plug-relay-troubleshooting.html

Mine did the same thing yours is doing. Only occasionally coming on, and when it did only for a couple seconds. Long story short, the capacitors were toast. Replace them and it'll likely work properly again. On a cold start you should easily get 5+ seconds on a warm day before the light goes out. Cold days will glow longer. You can always wait after the light goes out for a longer preglow, but if yours is like mine was, the max glow cycle was down to ~6-7 seconds.

[cmac2012]

I've read of the difficulties that one can encounter when changing glow plugs, it's good to hear a good report. FWIW, last night after posting I did a search and found an old post by H2O2 when he was in exile as Zeitgeist saying about the same thing, that the 603s didn't generally have that problem.

And wait, you identified the 3 bad capacitors and replaced them? That sounds like a good trick. I can only imagine that a working relay like that would cost a few pennies.

[Simpler=Better]

#1->Clean threads
#2->Apply nickel based anti sieze
#3->use a torque wrench to install

[Diesel911]

I am with those that recommend the typical Apply nickel based anti seize.

On the older VW Rabbit type Engines (and my Volvo Diesel which is made by VW) there is a thread insert kit for both the Injector and the Glow Plugs. But those would be from the 1980s.

I have had no issues removing Glow Plugs from my Volvo Diesel which also has an aluminum Cylinder Head.

What year is your TDI?

[dkr]

It is a 1997 Jetta MK3.

Dkr.

[Diesel911]

Originally Posted by dkr

It is a 1997 Jetta MK3.

Dkr.

Thanks. The part site I looked at said the heads on them are 10mm. That is skinny compared to the ones on mine.

[dkr]

I put them in the other day with 11 ft-pounds per the manual. It seems like just barely enough to keep them in there. So, what is the deal with the Mercedes ones? Did the MB overtorque them at the factory?

Dkr.