I replaced all 5 glow plugs last night on my '84 300D, two in the dark. A couple of observations for others bound to run into the sudden realization on the first cool morning of the year that they have a problem:

If for any reason you will be pulling your injector lines, or replacing your IP, take advantage of the opportunity and check/replace glow plugs. Sure would have made it a lot easier!

You can, however replace them all in one evening without removing anything. It just takes a little persistence, caution, and not droppping things where you'll lose them. I was concerned that I would not be able to get out #5, due to the oil filter housing, but in fact it may be the most roomy. #2 was a bugger, but a really short ujoint socket extension took care of it barely. Take care.

My dash light works again. It turned out when I pulled the plugs and tested them that three tested bad! And it started really easily this summer anyway. A fourth plug had the end shear off soon as I tried to remove the wire harness (it tested good....darn) and the fifth is now my spare.

Ben

remove the fuel lines to do that. doesnt take very long. makes the glow plugs a snap. the #5 is the only one i can do with them on.

tom w

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[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

I just replaced the Glowplugs on my SDL. Access wasn't a real problem as I had the Intake manifold off for other reasons, so it was one of those 'While you're in there....' jobs

One thing to watch for: When I went to test the completed job - after the intake was back in place - the dash Glow Light didn't come on and the engine didn't want to start. Checked the Glow-Plug relay and found the fuse had blown.
After further investigation I found the ring terminals on the ends of 2 of the Glow-plugs had turned enough when I had tightened them up to just touch the cylinder head and cause a short-circuit. They are insulated, but not completely. Once repositioned and the fuse replaced, everything was fine.

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1991 M-B 560SEL Arctic White/Grey 99,000 Miles
1987 M-B 300SDL Ivory/Palomino 229,000 Miles (sold but never forgotten)
2006 Volvo XC70 Blue/Beige
1999 Porsche Boxster Arena Red/Savanna Beige
1986 Porsche 928S Goldweiss/Brown

bhanson,

I would have done a resistance test first and just replaced the bad GP. That way I would have 2 new GP for spares. Since a GP failure isn't a no run condition and they can be replaced almost anywhere, I replace them as they fail, one at a time.

P E H

I had tested a couple and knew at least one was bad - plus it wouldn't start. I ended up with one spare (theoretically) of the bunch of old ones that tests at .6 ohms.

Ben

Should have addressed the other post too on removing lines. I haven't had the car long and don't know the conditions of any washers or gaskets that would need replacing. If I had a set I think it would have saved time removing the lines, but I felt I had too many variables to be sure, and it got dark before I was finished. I didn't want to find myself with anything leaking.

Should I not have been concerned with those things?

Ben

Well I was going to post a seperate thread on this, but no need now......
I replaced all five of my glow plugs last year, worked great. But now she is starting to act up again. I have to leave the key on an extra few seconds after the light goes out. Otherwise it is a rough start. Do you think I have a bad connection, or just an old relay?? This is a 83 300d 203k. I am worried about what will happen when it gets cold this winter..... That may be in November down here

I read every old thread I could on glow plugs before replacing mine. I read in several instances other people who had plugs that lasted less than a year, which equates to them essentially being defective to begin with.... However, conventional wisdom seems to assert in general they should last a very long time. I also found several people with strong brand loyalty.

I'd test them.

Ben

New glow plugs are nice!

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1981 300D 147k
1998 VW Jetta Tdi 320k
2001 Dodge Ram 2500 141k
1979 300D 234k (sold)
1984 300D "Astor" 262k(sold)
Mercedes How-To and Repair Pictorials
I love the smell of diesel smoke in my hair

Diesel Giant,

WWW.DieselGiant.com in your post not found when I clicked on it.

However when I clicked on my WWW.DieselGiant.com above, the url was found.

Anyone else have the same problem?

P E H

I read somewhere that if you don't ream the glow plug holes, your new ones will not last very long. I thought it would only inhibit performance at worst, but that is something to look into. Does anyone recommend unplugging the battery before this job is attempted? Is blowing the fuse a regular thing?

you do not need to disconnect the battery but by all means disconnect the wiring harness that plugs into the GP timer box. If you measured resistance from each pin in that plug to ground with an Ohmmeter after installing the GPs it would indicate if one had a terminal lug touching the block (ie. shorted)
It is common to blow a fuse if a glow plug shorts internally. They usually fail open like a light bulb.
The old loop style series connected GPs would short to ground if there was a lot of carbon built up and that makes it very important to remove carbon in those type of GPs.
OTOH the "pencil style" or parallel connected GPs cannot short to ground in any way external to the plug body but carbon could be a shunt path for heat making the plug take longer to reach temperature.
The worst case is when a pencil style GP is stuck to a body of carbon that has coked and is holding the GP in, you want to have solvent available to squirt in there and try unscrewing the plug very carefully so as to not break it off inside the head.

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'95 E320 Wagon my favorite road car. '99 E300D wolf in sheeps body, '87 300D Sportline suspension, '79 300TD w/ 617.952 engine at 367,750 and counting!

1983/300CD,

No need to disconnect the battery when working on the GP as long as you keep the key switch turned off. The GP can be energized only when the key switch is in the run position.

I never used a GP reamer and my GP last for years and years and tens and tens of thousands of miles. This is in 617 engines but the newer engines with the long GP may be a different story.

P E H

My GPs all tested just fine -- but the engine wouldn't start without lengthy cranking (ambient 50-55) ..... replaced the plugs & was back to 1 engine rotation & vrooom (or, more exactly, oom clatter). Dash light always worked, plugs always got juice ... That was 6 months ago & no problems since.

estod,

I am suspicious about your GP testing. What was the specific procedure you used?

Did you connect then individually across the battery after you removed them to see if they glowed?

P E H