300D Glow Plugs & Injectors.

[John Green]

I personally change my old looped GPs to a new looped GPs set. Even though the old set was working but I have to re-glow them couple of times to get the engine started. Ifoud no difference with the new set. I give you my word for it.

OK, fair call. I will go and do some research reading my Service bulitins and on the EPC to see if there is a MB upgrade for these. It would be kind of strange if Bosch have found a better system and MB have not gone with it........

These glow plugs are wired up in series like the loop style ones or do you have to modify the loom...?

[MB300D81]

MB have upgraded to the pencil GPs in later models 1981 on wards. They used in parrallel but used a smaller thread GPs.

These glow plugs are wired up in series like the loop style ones or do you have to modify the loom...?

No they are wired in barrallel. This is why if one fails the others will still get power to them. Just like in the later models 81 on wards.

See photo...

The earth wire at the end. Is no longer needed with these GPs. They are earthed from the block.

Regards

[Tony From West Oz]

John,
These would have been created after MB changed to parallel pencil type GPs. This is not to say that MB weren't aware of them or did not provide a service bulletin, but it would not have been a priority if they came out after the change.

There could also have been other problems which this change overcame.
I do not know whether:

• the injector spray pattern checked
• the valve clearances done
• injection timing checked
• compression checked

in the diagnosis of this issue, but the actual fault may have been due to one of these, and the new style GP was able to provide the additional heat to enable ignition when the engine was cold, overcoming the actual cause.

I do not have problems starting my early OM617 (with series GPs), although my GP relay in not present and I need to push button to activate the GPs, so perhaps I compensate for a similar issue.

This is not to say that this upgrade has no value, on the contrary, I believe that from Fitian's experience they are definitely worthwhile (I have ordered a set for one of my 300Ds).

Regards,
Tony
edited to hopefully fix the list and to correct spelling from "indefinitely" to "definitely" - Tony

[MB300D81]

There could also have been other problems which this change overcame.
I do not know whether:

• {*}the injector spray pattern checked
  {*}the valve clearances done
  {*}injection timing checked
  {*}compression checked

in the diagnosis of this issue, but the actual fault may have been due to one of these, and the new style GP was able to provide the additional heat to enable ignition when the engine was cold, overcoming the actual cause.

I do not have starting my early OM617 (with series GPs), although my GP relay in not present and I need to push button to activate the GPs, so perhaps I compensate for a similar issue.
Regards,
Tony

Tony,

You own/drive 2 x 300D so I am sure you know that GPs will only make a difference to starting the engine.

the injector spray pattern
the valve clearances
injection timing
compression

These things will affect on starting the engine but they will also affect on the engine performance while driving for sure. So if you are losing power or blowing smoke then it can not be GPs. While if it is hard to start the engine from cold and if you have to run the GPs cycle twice to get it started "hold the button for longer in your case" then this points the finger at GPs more than anything else specially if the car runs well after it starts.

If you install the new set of these GPs on your 300D where you have no timming relay, You better use a stop watch to test how long it takes to start the engine with the old style and compare it to the new style.

Cheers

[Helga]

Hello Sean,

Just wondering if you are noticing ANY differences since fitting the new injector tips? From what I have read they are usually said to make a big difference but if yours weren't bad to start with, no reason why new ones should make any improvement I suppose.

Did they cut down on the smoking much? Helga has been worrying me a bit of late in the amount of smoke she blows at the lights and when first moving off. I took her for a good run on the expressway down to Wollongong yesterday and left her on oil for when I got back home. I checked her out idling in the driveway and there was virtually no smoke in that you really had to get at the right angle with the light to see it and then it was just a slight haze, not the pall of a good size wood fired BBQ it had been just hours before. I also noticed it had more of that pleasing diesel clatter sound to it so maybe a part of scheduled maintenance should be a good highway run although I drive the thing everywhere flat out anyway so I'm not sure what the difference is!

Which tips did you fit to your car? Were they the Bosch ones or something different?

I still have the loop style plugs and don't seem to have any trouble with them. I can now start on oil from cold if need be which I couldn't before. Apparently the timer on my plugs burned out at some time before I got the car and was replaced by a button I can manually hold on for whatever time I want. I find this very useful and when I get a car with a working timer, I'll certainly wire in a manual button as well!

[pangit99]

Well to conclude this thread, the old girl made it to the snow and back admirably:

The roof box was for the luggage (and skis while we were there), and the boot was full of 150L of WVO, which was nearly enough for the entire trip! Even with this heavy load and me + 3 passengers it ran great on the Hume Highway, cruising at 110-120km/h. Going up the steep road to the top of the mountain (with slightly less load, as I left the WVO and luggage at the hotel in Mansfield) was also a breeze.

While I was there I used pump diesel in the startup tank and WVO mixed with some home heating oil in the main tank. Temps got down to around -2C, but I didn't leave it on the mountain overnight. It started no problems at the end of each day after 8 hours at the top of Mount Buller.

I've only just refilled the startup tank with 100% biodiesel and this morning (which was quite cold for Sydney) it started in a couple of seconds after one glow. Much better than before. So I'm pretty sure the new injectors have made a big difference there. The pencil style glow plugs also must have helped, but not so noticeable before I changed the injectors.

Apart from that I've not noticed a huge difference. Less smoke when running on WVO, but no noticeable improvment in power or engine noise. Not that it was bad anyway. But I'm glad I did it, as I'm pretty sure they were the originals (judging by the state of them and how hard they were to remove/take apart!)

One tip for anyone thinking of doing the same - I followed the guide on the Dieselgiant website, but I couldn't take the injectors apart by clamping the hex portion in the vice and using a 22mm spanner on the upper portion. They were way too tight. So I simply turned them upside down and clamped the 22mm part in the vice, using the 27mm deep socket with a breaker bar on the hex portion. Easy! You just have to be careful the socket does not touch the nozzle tip and damage it (mine just cleared it).

David I'm pleased to hear your "Italian Tuneup" helped with Helga! The nozzles I bought were Bosch ones (made in India), which I think are the only ones you can get in Oz these days.

[lockiedog]

I'm looking at changing the original series glow plugs on my 1976 300d to the parallel pencil glow plugs.

I am going to change the wiring from the 80 amp fuse to the glow plugs (so that its in parallel, without the resistors and not earthed) and keeping the rest of the existing loom and relay.

Pervious posts in this thread forum members have done this modification and I am wondering long term how has it worked? Was it worth the "upgrade". Did the original relay hold up or is it suggested to convert to a manual switch under the dash? Over time has the longer glow time of the "older relay" system burnt out the pencil glow plugs prematurely?

Where have people sourced these glow plugs from? I have recently confirmed that this Bosch part number 0250201044 is current but Bosch Australia don't carry them, they can get them but are very expensive (Quotes this week have ranged between $180-$225 for a single glow plug). There are Bosch sets of 5 on ebay from the states for US $107 plus postage.

https://www.ebay.com/itm/Set-of-5-Diese ... Sw-ctbepgq

Then there are also Bremi sets of 5 with wiring for US $129 plus postage

https://www.ebay.com/itm/MERCEDES-300-D ... 0005.m1851

Any experience or suggestions would be greatly appreciated

[John Green]

https://www.ebay.com/itm/Set-of-5-Diese ... Sw-ctbepgq

Then there are also Bremi sets of 5 with wiring for US $129 plus postage

https://www.ebay.com/itm/Set-of-5-Diese ... Sw-ctbepgq

Same link twice?

[lockiedog]

https://www.ebay.com/itm/Set-of-5-Diese ... Sw-ctbepgq

Then there are also Bremi sets of 5 with wiring for US $129 plus postage

https://www.ebay.com/itm/Set-of-5-Diese ... Sw-ctbepgq

Same link twice?

My mistake, I have edited the second link and should be right now.

[mathuisella]

I thought the older style plugs and the new ones weren't compatable. Forgetting about the wiring for a moment, the main thing they aren't compatable is because the holes in the head are larger for the older style plugs, so the new pencil type won't fit in and seal properly ?

I'm happy to swing a new pencil plug your way to test this if you like :)

Here's me when i was cleaning up plugs on the old yellow 240D, they just seem to be more chunky than the newer pencil type.

ox4zh.jpeg

https://www.youtube.com/watch?v=kUgO6Stx27I

[Tony From West Oz]

There is a pencil style GP for the pre 1980 OM61x engines.
Have a look at this ebay listing:
https://www.ebay.com/itm/MERCEDES-300-D ... SwlyJaFwqj
Here is one from Mercedes shop https://mercedessource.com/store/early- ... ersion-kit
There may be others which are cheaper.

[lockiedog]

I have actually fitted the pencil GP in replacement to the old loop GP. They do make a huge difference.

The old control unit "relay" in the old models pre 80s is designed to stay on longer compared to the later models because the GPs on the late models are fast glow plugs.

The old relay will get the pencil GPs to stay on a little long wich is even better.

I am now able to start from cold much easier then when I have the looped GPs.

The reason I dug up this old thread is because its all been discussed previously if its possible and how to wire it up etc but I am just wanting to hear from forum members personal experience's with the modification long term. Does the original relay hold up or is it recommended to bypass the relay and have a manual switch under the dash for pre glow timing? Do the glow plugs hold up (longer glow time of the old original relay burn out pencil glow plugs prematurely)? Was the modification worth it?

I posted two links in my previous post to ebay suppliers of these glow plugs one is the same as Tony just shared. The other one Tony shared is to Mercedes source which the glow plugs are of the Monark brand, doing a little reading on US sites you quickly find a lot of complaints about these Monark glow plugs with people experiencing failure within months due to poor quality.

In the 60's-70's era Loop style glow plugs wired in series were common in diesel engine's (auto, marine, Ag) With the advancement in technology in the late 70's a shift to pencil style glow plugs wired in parallel was seen. Glow plug manufacturers began to supply pencil style glow plugs that could replace the loop style glow plugs in older engines that were originally designed for loop style glow plugs. As like the om61x series engines loop style glow plugs are generally larger in physical size and have larger thread diameters hence why manufactures began to supply pencil style glow plugs with large thread diameters to fit into older engine's. It became a fairly common modification for farmers to do to their tractors with benefits being quicker starting, smoother running from start up, less smoke on start up and being wired in parallel if one glow plug failed the rest would still work.

[tsharkey]

I read somewhere those older style relays are worth a fortune. If that's true I would sell it and wire in the new style relay. Should be fairly straight forward as it wants

Input
+ve Heavy Gauge from starter (you will have that)
+ve Ignition on run \ start (Fuse 12)
+ve start (From Neutral Start Switch)
ground

Output
+ve Light into cabin - You were adding a line for the switch anyway
Line to Glowplugs (I have one of those spare)

Diagram attached

That way you will get the diagnostics off the relay when the plugs start to fail.