Can anyone explain in specific electrical terms why an MB Diesel will not start immediately with a jump when its battery is totally dead.

Does a dead battery "draw" so much current charging when connected to a 14v source that there is insufficient current to engage the starter?

I'm sure that the current draw of the starter makes a difference...years ago the starter in my Toyota Corolla looked like a hobby kit motor...about the size of your fist. But in my 123 diesel, the starter is a moose! I'm sure it is very easy to jump a corolla, but not an MB Diesel.

Is it a function of the gauge of the jumper cables? I recently read on a forum post somewhere from an MB Diesel owner that with 1 gauge jumpers (very thick copper conductors) he "could jump his car even if the battery is dead without having to wait for it to charge".

Is it because most cars have small batteries and can't provide sufficient cranking amps to meet the demand of an MB Diesel?

In my own experience, I recently had a dead battery....came back from a business trip to the airport where my 123 diesel wagon was parked, and the battery was so dead that it barely caused the dash lights to flicker. A guy who worked for the garage came over to give me a jump with a brand new Ford F250 pickup and a set of 20 foot 4 gauge jumpers, and it would not turn over my starter immediately..we had to let it run while connected for about 10 minutes...basically giving my battery a quick charge...before it would turn over.

If you had a dead battery,and needed a jump, couldn't you just disconnect the pos. cable on your own dead battery and connect the jumpers and expect your car to start immediately? Then just reconnect the pos. cable?

Finally, with certain vehicles, I understand that you can damage your alternator when jumping....something about the diodes?...can anyone explain this? Who's at risk, the car getting or giving the boost?

Thanks,

Mark

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1984 300TD Wagon, 407,800 mi (current daily driver)
1985 300DT Sedan, 330,000 mi (gone to that great autobahn in the sky)

Its the jumper cables. You need a thicker gage to support the current. Your toyota engine IS a hobby motor compared to these things. Also if its cold and oil is not synthetic its gonna take alot more to turn it over. The battery acts like a capacitor as well and will need a charge.

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

I have no issues jump starting the 300SD from either the BMW or the Jeep.
neither of those cars has a robust charging system as they have alternators in the 35 amp range on the CJ and maybe 65 amps on the 528.

I just connect the batteries together (I know that is not the approved method), start the donor car and then crank over the MB. I think you are having issues where the glow plugs are taking too much power. You need to wait about 45 seconds for them to fully glow and shut off before trying to crank the engine over.

I also have THICK cables I bought from Sears years ago. I think they are 2ga or at the least 4ga.

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You can't just trow the cables on and start cranking. You need to let your battery be charged by the jumper for a few minutes before you try anything.

Even the smallest jumpers will work if you let your battery charge first.

Pretty much a combo of all the factors you listed.
-dead large capacity battery puts a big load on the supplied jump.
-heavy duty diesel starter, another big load.
-cheap small gauge wire jumper cables don't carry enough current.
-charging system capacity of jump vehicle. On most vehicles they are sized to supply the needs of that vehicle, not 2 vehicles. Some service vehicles are the exception.
I have had some luck letting mine "charge" on the other vehicle's system for a while and then trying to crank the engine.

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'83 300D Turrrbo 295K miles

It all depends on the source. If you have a very large battery as the source or a 500 amp starter/charger, the source is sufficient.

Correct.

1 or 2 gauge cables are excellent for the task. However, the clamps are the real determining factor as to how successful you'll be.

A smaller battery will generally provide sufficient voltage for a much shorter period of time. If you can get it started in five seconds, any battery will do.

The problem was not the battery. Getting sufficient current through the clamps is the issue. The 4 gauge jumpers are marginal for completely dead battery.

This wouldn't be advisable. Most batteries are not completely dead and you'd be relying compltely on the cables.........usually not sufficient due to the clamps.

If you connect the cables in opposite polarity, you can certainly damage the alternator and may damage other circuits in the jumped vehicle.