Strange problem on a 93' 300 TD non turbo.
Sometimes, engine cold or warm, after starting the engine, 5 - 10 seconds later, the glow plug light lights up again and goes out when the GP relais cuts out. I mesured the glow plug resistance at the plug on the relais.
The values were from .45 Ohms for No 1, untill .70 for No 6. I think those differences are due to the different length of wiring.
Well, I did a search on this topic and found out that checking this way the GPs don't tell everything. A current draw mesuring with a battery charger would be better yet. But for the moment I don't have one strong enough and with a decent Amp meter..
So what do you guys think about it : replacing the relais ( the easiest way ) or the glow plugs or worst scenario, both.
Before you start questionning : the car starts allways excellent, warm or cold and we had 10 days temperatures below 0° C.
Thanks in advance!

Danny

Hello 95300YDT-A
Save money, do the glow plugs first.
Have a great day.

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Saving money?

I should think replacing the relais is the cheapest solution.
Will be replaced in 5 minutes by myself.
The glowplugs equals (6 of them) the price of one relais but are NOT a 5 minutes job. More of an half day's work ( if everything is going well and I don't break to mutch). I know by experience : the plastic high pressure retainers will be brittle and to be replaced as are the fuel return lines and god knows what other stuff : gaskets, other "retainers", etc...
Well, the good news is : my Indy is of good will and will loan me a new glowplug relais. So I will be able to check out the difference and I'll find out what to do...
One thing is for shure : if that damned manifold has to come of, I will be replacing ALL the glow plugs (what I never do with my 603). Just don't want to take it of 6 times !!!
Thanks for your reply anyway,

Danny

The relay rarely fails. I believe the light coming on after start is on purpose - read the owner's manual about that!! I think it's telling you a plug is bad. You are correct though, change all 6 plugs at the same time. Someone just posted a nice tutorial here:

Finally - Step By Step Glowplug Change - '98-'99 E300!

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Gsxr,

That's good advice. I will reread the manual about this "behavior" and will replace all six GP's when the manifold cames off. That's something I don't have to do with my 603. Untill now I only had No 4 or 5 bad and with the right tools it took 5 minutes to replace!
The topic you mailed I read it when I did a search before mailing this thread.
Our Benz-brother is earning an Oscar nomination for that posting, I hope ?
Or at least a Welldone Job ?
Thanks for your reply anyway !
Greetings,

Danny

Hi Danny,

A good test of glow plugs is as you say, by measuring the current they draw. I used an ammeter from an old car that used a Dynamo (remember them?) You cant get enough current from a charger for this test, so just connect the ammeter between battery + (or the common input wire at the GP relay) & each glow plug in turn. these old meters usually read about 30-0-30. each glow plug shoud take about the same current, maybe 10/15 amps. Any that are different are probably faulty. I take your point about plugs being hard to get at, Mine is a 5cyl 605, easy access to plugs.
Hope this helps
Peter

Thanks Peter,

That's a good tip about that Amp meter. Yes I do remember them.
In fact there is still one on an old tractor that is hanging around here.
I am going to try that only because I am curious.

Danny