78 300d loop style glow plugs
 

Got a quick question. This car has the plugs in series and the power from the glow plug relay hooks to the #5 cylinder and then on to #1. The #4 plug keeps burning in half. Can't figure out why.
Any similar problems or suggestions?
Thanks.

I'd check the connections to the #4 plug and the #3 plug and make sure the ground on the end is good. You could also do away with the series plugs and put in the pencil style parallel plugs, put in a wires to each one, and remove the ground, and you'll have a parallel style system with pencil plugs. They make pencil plugs that fit. I did it to my 240 a while back and haven't looked back.

X2. Switch to the retrofit pencil plugs. Better plugs, quicker starts. Threads on here give the part number for the plug. No need to switch out the relay.
I have no idea why one plug would keep burning out unless it was getting excessive voltage which might happen if the power was bypassing plugs 3,2 and 1 and going directly to ground.

Ok, thanks. I had removed the toaster style loops loop from and to each plug, cleaned for good connection, cleaned the ground etc, had the system working great and then the #4 plug melted. Scratched the interior of precombustion chamber and blew out with air, replaced the plug again and it lasted 1 day.
The suggestion of installing the pencil style plugs; I've read about them, but how can you not replace the relay when switching to them?
See actually I'm working on a neighbors car, got the inop glow system working and then the issue with the #4 plug started.
I appreciate all the good advice.

Read the old thread. Talk was there was a kit to convert. I haven't located that kit. Some say that the relay (old type under steering column) doesn't require replacement.
Need some input.
Thanks.

X3 on switching to the new style plugs, you wont regret it for a second. You can use your same relay just cut the glow time way down. You should go to a 80 amp fuse also.

Steve; sent you a pm.

Where can I get the pencil style glow plugs with the large thread to fit the head?

i have a complete set of loop style glow plugs never used brand new

Thanks for the offer of loop plugs, but I refuse to install anymore because #4 will melt.
Thanks.

Search for retrofit glowplug part number here and then order them from Fastlane. You'll have to make jumper wires to go from plug to plug and then connect the plug nearest the firewall to the original hot wire from the fuse box on the firewall. Delete the original ground wire at the front of the block. Old relay in 123 chassis will work fine.

kerry states it well. I did this on my 240 without changing the relay. You can change the relay but it's not necessary.

Get them right here, price is good and they support this forum, click on "parts" at the top of the page.

KIT for converting LOOP series GP to hotter pencil parallel system
 

F1101-88322 KIT for converting LOOP series GP to hotter pencil parallel system
http://www.peachparts.com/shopforum/mercedes-parts-reference-library/178765-f1101-88322-kit-converting-loop-series-gp-hotter-pencil-parallel-system.html

A bad injector on that cylinder can burn out glow plugs like that.

Hey thanks to all for the info. Hunter sent me a link for the plugs and the kit. Looks like this is the direction I'll go.
Ya all keep up the good job.
Thanks.