Just changed glow plugs on an 85/300TD - PeachParts Mercedes-Benz Forum

Mistel · #1 11-18-2007, 09:39 AM

I just changed the glow plugs on my 85/300TDT. I am not much of a mechanic, but I managed to do it and the car started first try! I wanted to tell other novice mechanics like myself that it is not that hard. I took the fuel lines off with a 17 mm wrench, I think that you have to remove them. Even with the lines off the last plug is tough to get at. To reattach, I put the all the lines on finger tight first, then tightened the bottom nuts, cranked it over a bit to try and get some of the air out of the lines, then tightened the top.

Peter

kerry · #2 11-18-2007, 10:15 AM

Good work! It is possible to do it without removing the injector lines. In fact there's a thread on here polling whether members remove the lines or not. Did the ones on my SD last week without removing the lines. It just takes a little planning and a willingness to get the back of your hands scratched.
Hint: jam some rags down between the IP and the block to catch those little nuts holding the wires on when you drop them.

cestes · #3 11-18-2007, 10:27 AM

I tried mine last weekend... I managed #1 and #3... Then I read that it's easier if you remove the fuel lines!

Good tip about the rag... I dropped my wrench at least 5 times down between the block and IP. I used a hook made from a coat hanger to fish it out!

#4 11-18-2007, 10:47 AM

Yup, you can do it either way. I never take off the fuel lines, but you do have to squeeze your hands in pretty tight spots.

charmalu · #5 11-18-2007, 12:19 PM

A little anti seize on the threads helps, especially next time removeing them.

One of those magnets on a stick work wonders retrieving those dropped little nuts. amazing how they seem to disappear

.

sometimes it`s hard to get a 17mm wrench in to loosen the fuel line nuts, so I use a flare nut crows foot.
I have the official MB 17mm wrench to remove the fuel lines, and it was starting to spread open. some one realy cranked down at sometime.

I use 2 washers on either side of the wire, then the nut. I have had the center of the glow plug shaft turn when the nuts don`t want to give. Iam sure it damages the plug inside.

I just take off the fuel lines, just easier for me. then it is all about me when it`s my rear under the hood

.

My two cents worth.

Charlie

pawoSD · #6 11-18-2007, 12:23 PM

I prefer to do it with the lines on....makes it more painful.

And, no rags to catch the nuts....just to make it more tedious and stressful.

vstech · #7 11-18-2007, 03:19 PM

I have done it without a scratch with the fuel lines on. the tip I have is to remove the steel line seperators. that is what will scratch up your hands...

lws1 · #8 11-18-2007, 03:45 PM

Quote:

Originally Posted by Mistel

I just changed the glow plugs on my 85/300TDT. I am not much of a mechanic, but I managed to do it and the car started first try! I wanted to tell other novice mechanics like myself that it is not that hard. I took the fuel lines off with a 17 mm wrench, I think that you have to remove them. Even with the lines off the last plug is tough to get at. To reattach, I put the all the lines on finger tight first, then tightened the bottom nuts, cranked it over a bit to try and get some of the air out of the lines, then tightened the top.

Peter

What kind of a wrench did you use to get the glow plugs out? a ratchet? a regular wrench? if so, which end? I gave up the first try because I could not get the 2 that I tried to turn. Someone suggested trying it while the engine was still warm and am going to try that. But really, what's the best wrench when they are in there solid? I don't know that they have ever been changed, 135,000 miles on my car. - Thanks, Lance

Mistel · #9 11-18-2007, 04:32 PM

What I used, and remember I consider myself a novice, is the closed end of a wrench to loosen it. My thinking being that it will grab the GP better, and be less likely to slip off. To get the GP out the rest of the way is a pain with a little wrench, but I found it tough to get a ratchet and socket combination that would fit. The GP is too tall for a short socket, then not much space with a deep socket. I think there is something called a wobble attachment that I believe would work. Maybe more knowledgeable people will chime in.

Peter

#10 11-18-2007, 05:00 PM

Quote:

Originally Posted by Mistel

What I used, and remember I consider myself a novice, is the closed end of a wrench to loosen it. My thinking being that it will grab the GP better, and be less likely to slip off. To get the GP out the rest of the way is a pain with a little wrench, but I found it tough to get a ratchet and socket combination that would fit. The GP is too tall for a short socket, then not much space with a deep socket. I think there is something called a wobble attachment that I believe would work. Maybe more knowledgeable people will chime in.

Peter

I use a short box wrench to get them started, then an open end wrench, then just spin them out with my fingers.

pawoSD · #11 11-18-2007, 05:18 PM

Either Wednesday or Friday/Saturday I am replacing the relay and all five glow plugs on our 300D. There's something screwy with the current setup in there. it looks good (all stock/normal)....the plugs "test" good, but....it sputters and kicks when its cold out, and very much dislikes starting when its below 30F. It fires right away, but it feels/sounds like at least 2-3 of the cylinders don't fire right away. And a lot of white/black diesely exhaust in the first 15-20 seconds of running when cold. None of that when its over 50 outside. Engine has great compression. After the initial 15 seconds of being upset, it will idle smooth and solid, no stalling or sputtering. Almost no detectible blowby.

Heres the odd part. When you turn the key to glow position, the light comes on, for about TWO seconds, then goes right out. The relay stays on however, but clicks off after about 10-12 seconds. Wayyy too early. In my car (with the afterglow modern relay) it will stay energized for up to 45 seconds before cranking and then 2-3 mins after it starts, same on my dads car with a MB normal relay. (minus the afterglow) And, mine lights the glow plug light longer on cold days (a lot longer) than on warm days, same for the other car. The 300D blips it on for 2 seconds no matter the outside temp.

My guess is that the relay is just plain worn out. We'll see how the new kit, with 5 new bosch duraterm plugs + the modern afterglow bosch relay....works out. Hopefully very well. And I hope the plugs come out ok....

#12 11-18-2007, 05:47 PM

Quote:

Originally Posted by pawoSD

Heres the odd part. When you turn the key to glow position, the light comes on, for about TWO seconds, then goes right out. The relay stays on however, but clicks off after about 10-12 seconds. Wayyy too early.

Sounds like a relay problem to me, the "afterglow relay" is definitely the way to go.