1979 300td

I'm trying to put together a forensic scenario for my rather serious, and seemingly multi-factorial, starting troubles of the past month or so. I think the only sensible explanation involves a (filament, wired-in-series) glow plug failure AT THE END OF the first start with a fresh battery. I'd like to get a sense of how likely this is, if anyone wants to weigh in.

Thanks!!

If a glowplug burns out with the install of a new battery the old battery was probably pretty weak and wasn't giving the GP the amps it should have been getting. Otherwise you have something wrong with the GP fuse, relay or bus wires between GPs or the gorund. You could also have tired glow plugs. I'd make sure you are getting 12 volts to the first plug and that the ground is grounding properly. I belive the series plugs loose 1.5 volts at each plug, so you should get 12v at the plug nearest the firewall, then each plug after that will be 1.5 volts less than the previous one.

Also if you change all your plugs I highly suggest putting in the pencil style plugs. Do a search here on converting from series plugs to parallel plugs and you'll find all you need. It's a simple mod. Put in the large bodied parallel plugs and put a wire connector between each plug and remove the ground. I did this on my 240 and it works great. Much better start ups.

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Use Bosch glowplugs and burnouts will be extremely rare.

X2 you will never regret doing this, I promise

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1985 Euro 240D 5 spd 140K
1979 240D 5 spd, 40K on engine rebuild
1994 Dodge/Cummins, 5 spd, 121K
1964 Allice Chalmers D15 tractor
2014 Kubota L3800 tractor
1964 VW bug

"Lifes too short to drive a boring car"

Whatever you do dont use autolite.

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1995 E420 Schwarz
1995 E300 Weiss
#1987 300D Sturmmachine
#1991 300D Nearly Perfect
#1994 E320 Cabriolet
#1995 E320 Touring
#1985 300D Sedan
OBK #42

You mean "Ought to Light"?

Yeah I agree, Bosch!

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RRGrassi


70's Southern Pacific #5608 Fairmont A-4 MOW car

13 VW JSW 2.0 TDI 193K, Tuned with DPF and EGR Delete.

99 W210 E300 Turbo Diesel, chipped, DPF/Converter Delete. Still needs EGR Delete, 232K

90 Dodge D250 5.9 Cummins/5 speed. 400K

Gone and still missed...1982 w123 300D, 1991 w124 300D

I have an arm-chair analysis:

With the series-arrangement, all glow plugs are supposed to have equal resistance, then each plug gets equal voltage, which creates equal heat.

If one plug is weaker than another, it will have higher resistance, which will mean higher voltage, and higher heat. As the wire heats, its resistance decreases, which increases the voltage and heat further.

Therefore, replacing one or more glow-plugs will naturally create a disparity between them, so that some are getting too hot, others not hot enough (typically a new one will have lower resistance). The weakest ones are always getting more heat until they fail.

The best scenario is to replace them in sets, so that they are all the same resistance and none will have significantly higher voltage than any other. Of course buying a new set might justify simply buying the "pencil" style that work in parallel.

The newer style all are parallel, in which case all get the same voltage, regardless of resistance, therefore they don't kill the weak one and longer life should be the result.

Your set probably had a weak one (or two), and the additional voltage/heat of the new battery was what put it over the edge.

For the math behind this:

In a series arrangement, the current is constant through the entire circuit.

I=E/R or current=voltage/resistance. Since the current is constant, as the resistance increases so will the voltage (if R doubles, E would double also to maintain I as un-changed). P=IxE or Power (watts or heat) = Current x Voltage.

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Gone to the dark side

- Jeff