115 Glow Plug Upgrade
 

I'm looking to upgrade my '69 220d to parallel glow plugs...

I've read of some people not using a relay with the parallel plugs by doing the following:
short out the glow indicator
replace glow plugs with Bosch 0 250 201 044 (Duratherm)
remove the resistive wires between plugs and replace with low resistance wires
remove the ground connection

I know this setup won't give me extended glow after startup but I'd rather give that up and save the cost of the relay. Another option would be to use a W126 relay I procured and do the cheap man's afterglow by removing one of the wires from the relay.

Anyway, I'm looking for any success stories related to the above. There seems to be a lot of info on relay-based upgrades... I really need some input on the old style pull knob based upgrade.

Have you thought about an under-dash toggle switch for the upgrade GP system with its own wiring harness independent of the rest? This strikes me as path of least resistance, skipping the pull knob GP switch but keeping the pull knob idle adjust function intact. The only prob would be that you might lose the salt-shaker/hornets nest GP indicator in the process though.

But the real question is why the upgrade.... Are pencil plugs really that much better then loopers, or is it alot of hype and just a matter of cutting down on waiting time to start the engine?

I'm convinced its a big upgrade. Thinking theoretically, in the loop system a whole lot of power is wasted in the resistive lines, glow indicator, etc.

From the feedback I've seen on relay based loop -> pencil conversions, the difference is huge. I've read a couple of posts on the pull start loop -> pencil conversions and people report much reduced glow cycles (~30 sec down to ~10 sec).

Your suggested setup would require a relay... the benefit it would provide is manual controlled afterglow. My glow indicator lights very dimmly anyways... it is pretty useless so losing that functionality is no big deal.

Also looking for a Bosch p/n for the glow plug to glow plug wire shown below... 3 required... can anyone help?

I keep reading about this upgrade. I like the idea of having a parallel system so if one plug burns out, the whole system doesn't die, but I'm not sure I want to upgrade.

What does the relay in the kit do as far as timing? Does it actually activate the glow plugs for a period of time, then shut them off (like on the newer diesels), or is it merely to handle the switching of the electrical load? Do you still have to hold the start knob in the pre-glow position or would the system click on and off automatically?

I think the series system is 50A where the parallel is 80A, so I could imagine without a relay, you will destroy the pull-start switch. But I wonder if you could get away running the conversion glow plugs with a simple Radio Shack relay to handle the switching, an 80A fuse, and some homemade wires to connect the plugs.

And would you actually have to remove the coil/glow plug light in the dash? It would still operate in series with the parallel plugs wouldn't it? Might lower the current a little but I can't imagine it would be much. Maybe it would actually help the plugs last longer.

-AC

good point on the current... didn't realize the parallel system was 80A. Where did you get this number from? The relay itself is rated for 80A but there may be some marging built in to this number. BTW, I don't think you can get an 80A radio shack relay.

I know there has to be someone out there who has done this conversion...

The other thing I've been thinking about is to use the output of the glow plug light in the dash to activate an external relay (I have a GP relay I pulled from a 126 300sd)... not sure how the high resistance of the GP light in the dash will affect operation of the relay...

Actually I probably have the amperage numbers wrong. I was just thinking about the fuses I've seen on newer 240D's - with the series system I think it used a 50A fuse and with parallel, 80A, so the actual current drawn would have to be less. I think our 4-cylinder W115's still use basically the same 1938 technology as the original 160D - there were no relays back then, so they had to find some way of handling the high current of heating the glow plug elements at 12v (it was probably even 6v with the really old cars).

There are some other threads about glow plug replacement on 220D's and older 240D's if you search the archives.

I've also heard that you are supposed to use a special reamer to clean the threads and holes when you replace glow plugs...anyone know where to get one of these?

-AC

Did you look at the pictorial?

http://dieselgiant.com/mercedesdieselloopglowplugrepair.htm

nice link... it is helpful but doesn't cover the older pull knob glow plug switch. my 220d does not have a relay.

If the glow plugs are changed to fast glow then will it interfere with the indicator loop glow plug on the dashboard? Aren't they different voltages?

I removed the loop and shorted it with a short piece of 12ga Romex copper wire (solid wire, not stranded). I'm only getting ~9V at the plugs when cycling... I'm thinking there is a big I-R drop from the battery, through the dash switch, through the shorted glow indicator, and to the glow plugs. I have a relay that I salvaged from a 300sd and will be installing this soon... it will be triggered by the output of the starter knob (which used to drive the glow plugs directly).

Power is a V^2 relation so I figure going from ~9V to ~11.5V will give me a ~60% increase in power (and heat) at the plugs...

Regardless, yeah, the indicator function goes away and without the relay it is a pain to determine if you have any open glow plugs (they aren't isolated from one another).

Does the glow plug system work even if the dash GP is left in place?

Out of curiosity how many seconds of glow time are required with the existing configuration jumping the dash plug you have on your 220?

The dash glow plug is resistive and in series with the other glow plugs (at least while cycling the plugs... I think it is taken out of the circuit when actually engaging the starter).

Let's assume that the indicator light has a resistance of 'R' as do the glow plugs. The plugs are in parallel making their equivalent resistance 'R / 4'. Assuming zero resistance elsewhere (not really true... see my pervious post about 9V), this would mean that the total current is ~ 12V / (5R/4) = 9.6R A. Getting rid of the glow indicator increases the total current to ~ 12V / (R/4) = 48R A. Big difference.

Anyway, this was the logic that I went through that said, yeah it makes a big difference. The 12Ga romex fits perfectly in the glow indicator spot (near the same diameter). Get a small piece at a hardware store if you don't have any handy at home.

My glow time decreased significantly... from ~30 sec (series) to ~15 sec (parallel). With winter coming I'd like to push things even further (hence my plan to use a relay).

Cheap Relay
 

When I went to manual glowplugs on the 300SD I used a $10 lawnmower starter relay this handles the current of five plugs and has been in service for some 5 years, I never did get around to hooking up the idiot light BUT the healthy clunk of the relay tells me that something is about to happen.

Happy Starting


Steve

bosch duraterm
 

pdxwaker,
Hi, not did dig up old posts, but did you ever complete the conversion of your 220d to the parallel, pencil style system? If so where did you hook up the green wire? I am in the process of doing this upgrade at the moment and am stumped by the limited directions, or maybe its my limited electrical ability:D ! Anyway, any help would be greatly appreciated.
thanks eric
1968 220d