Afterglow and the Violet Wire
 

I posted this on the mbz.org diesel list earlier today:

As many of you are probably aware, if you snip the violet wire at the GP relay, you can get your GP's to glow for an extended period after the engine is running. This should theoretically reduce smoke, emissions, and coking issues. The problem is that snipping the wire also forces the GP's to run 'afterglow' even when the engine is warm, which will diminish the life expectancy of the plugs. Many folks have wired in a manual switch to turn off this feature, but I wanted a more 'hands-free' operation.

I installed a thermally switched relay into the GP relay's violet wire circuit. I used an NC (normally closed) relay from a Volvo 700 series fusebox. These are a 5 terminal relay, similar in look to the familiar 4 terminal NO (normally open) versions used in Euro headlite conversions and countless other little projects. These NC relays have an additional 87a terminal to which one side of the violet wire is connected, opposite the 30 common for the other side. http://www.the12volt.com/relays/relays.asp Be careful of other similar 5 terminal relays with an 87b terminal--these are just NO relays with two bridged terminals--these won't work.

I piggy-backed onto the 50 C thermal switch above the thermostat housing on my '87 300 td OM 603, which is apparently designated to assist and smooth cold shifting in the transmission.

When the relay is energized, the violet wire is snipped--afterglow enabled. In this phase, the 50 C thermo-switch has continuity with ground.

When the relay is not energized, the violet wire is bridged--afterglow is disabled. In this phase the thermo-switch has no continuity with ground.

I'll let you know how well this works in real world situations.

That's ingenious! I will investigate this further and will wire up a switch to mine. That is if my relay HAS a purple wire.

I believe all MB GP relays for the OM 616/617 and OM 601/602/603 series engines have a purple wire. All of the later OM 606 engines, and possibly some '90's era OM 603's had an afterglow relay installed at the factory. Try the switch first, then if you like the results, go for the relay option.

Good luck.

I'll just stick with the switch. That way I can keep her glowin when I want. I have no problem with a switch.

This is a great way to add "afterglow" cheaply, although plug life will be less than normal (duh). At next plug replacement time you could get the special afterglow-rated plugs which would help. A full factory conversion (for the 603) is expensive- you need the late relay, plugs, temp switch for the cylinder head, and some custom wiring... $200+ last time I checked. The relay+50C switch trick costs about ten bucks, tops, for a new relay. I've been meaning to do this on my car and haven't gotten around to it yet. Hmmm... maybe this weekend....

:D

Bump! I finally did the install last month, after discovering two dead plugs (only 20kmi old - don't buy Monark brand, stick with Bosch or Beru.) Anyway the mod works GREAT. It's 100x better than simply yanking the purple wire, as it only afterglows when cold. Wish I had done this a long time ago...

:) :)

Cool, need to look at my car and see about it. Would help cold weather starts a lot.

I suggest more folks give this mod a try, as it really does smooth out those cool early morning startups.

Thanks - my 603 engine is particularly cold natured. Starts up instantly and runs smoothly, then within about three seconds when the glow plugs cool down it smokes and rough idles. Less of an effect when I am patient enough to run an extended glow cycle. :) But what it really needs is the afterglow system that MB went with in the 1990s.

I want more direct control so I'll probably go with a toggle switch and indicator light. This is a low current-carrying wire, right?

Ken300D

Correct. You can make it look factory by using a rocker switch in the center console or above the ACC unit, if you can give up one of the stock switches... the fader is often bypassed when installing aftermarket stereos, that's the first candidate, second would probably be the antenna level switch (can be hardwired for 'full up' whenever the radio is on). Or you can get new (or used) wood with extra holes, but that's pricey (and hard to find used). If you add an aftermarket switch setup, try mounting them next to the headlight switch - they'll blend in pretty well over there.

:)

Nice idea. Bosch has incorporated this feature in the new glow plug relays. I think this is the kit that Phil is selling this month for 10% off. About $100 with 4 or 5 new glowplugs.

Yes, but if you have a 116 you are out of luck........the relay is different on those........ :mad: :mad: :mad:

That's for the OM617 engines only. There is no retrofit kit for any OM603's. You have to either do this mod, or build your own kit using factory afterglow parts from 1990-95 model OM603's. That's the preferable method but the cost is ~$250 for the relay, coolant temp sensor, and six afterglow-rated plugs. The 'poor mans' 603 mod with the 50C switch and relay gives almost the same effect for under ten bucks. Hard to beat that...!

:D :D

Potomac had a bunch of used OM603.97 GP relays on ebay last week. Was tempted to go for it as they were going cheap...

another variation of this idea.using a 555 timer ic and solid state relay to give you a fixed duration after glow.this could be packaged in a 35mm film canister.advantage here would be longer life on your glow plugs.details to be worked out