Yes, thank you I am aware of all of this, that is why I asked if it was possible for a battery to hold the proper voltage but not be pushing out enough amperage.

since this battery had low voltage, I am wondering if it was bad off the shelf, and even though it is stamped 'ok' by the guy at the counter of a McParts store, and seems to be holding proper voltage, that it is not putting out enough amperage to crank the starter over.

@barry, thanks let's see if I can cover anything I have yet to mention.

I have tried it with the glow relay in and out of the circuit. I also tried it with the alternator leads off, to see if it was a problem up front. Neither had any effect.

It really does feel like a bad starter. Cabin lights are all nice and bright, until I try to engage the starter. There is a little click, and the cabin lights will remain dim as long as I hold the key in the 'start' position.

When I had the starter tested, the bog boss had t come over to position the ground (where the small violet wire connects with a screw). He said something baout it being 'broken' I thought it was just that I left the screw at home thinking that if I bought a new one I would need the screw. He sort of threaded one jaw of the alligator clip into the hole, and like I said, it tested good.

He said it sounded funny, but that it was extending, and shrugged and said something about it being from an older model maybe sounding different than he was used to.

All that said, I think I will go and try the other battery tonight, and then tomorrow try and tackle the engine spin thing.....


EDIT: OK, I swapped the battery out from the red car and the same thing happened. So I left the key in the start position as long as I dared. It sounds like the solenoid is clicking, but I am not 100% sure.
I am sure, though, that that led to some insulation smoke and VERY warm wires. Won't do THAT again! So it seems like there is a short and it is at the starter.

The ground off the negative battery post was warm and the cable to the starter was warm. Nothing else was warm, including the starter itself.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Battery good? Are you sure? Are you sure the power is getting to the starter?

Starter good? Wires from battery clean and tight?

Solenoid good? Both wires clean and tight?

I think you have a loose or dirty connection between the battery and the starter or body ground from the battery to the inner fender. Check that out.

You know some starters will turn if you tap them with a hammer a few times. I'm talking about sharp raps with the wooden handle not hard enough to bend the housing.

So, I used a battery that was able to start the 240D parked in the same garage, and the guy at the McParts store says the new battery is good.

Same outcome.
Not sure about the starter electrical at this point, but it did Pass a bench test.
I think the solenoid is clicking, but not 100% sure. The post but not the solenoid gets hot if the key is left in the start position
All wires are clean and tight - for sure.
Haven't tried the tap trick yet....but right now I don't think it's the starter motor....that spun and extended at the bench test.


BTW, after really pushing some current and getting those wires warm, I dropped the battery back in the red car and it started up in less than one turn of the strater motor as usual....so I think the battery is fine.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

Empirical test(s) for batteries:
1.Testing the Electrolyte (In each Cell) with, a fully charged battery.

2.12.75 is a fully charged 12V.

3.Load test with at least a 500 Amp carbon pile tester.

[Swapping batteries around under Full Moons only confuses the Issues.]

HOT Cabling IS High Resistance (Or a Dead Short).
YOU HAVE ONE OR THE OTHER!!! [Maybe Both]

(I suspect you also have a BAD reman Starter.)

(AND an Overly Optimistic Voltage Meter.)

[Look at the Rocket Scientists working at the Automotive Big Box Store who
tested your "Starter",You know you wouldn't let them work on your MB.
Why do you think they're capable of testing a Starter?]

The quickest way for you to define your problem would be to put a Direct Current "AMP CLAMP"
on the Cable that gets HOT and see what the Starter is "Drawing" (If at All).

The Electronic "Gee Whiz" testing Box that Advance Auto uses will easily tell Y'all What's What.
Cables and Hall effect clamp hook up under the Hood without disconnecting ANYTHING...
AND It's the closest I've seen to Idiot proof.

__________________
'84 300SD sold
124.128

I am with you on the starter. The starter is reman, but came with the car....
The problem started with the glow relay engaging randomly while driving.

The car became slightly harder to start, until one day I stopped on my way home from work and car wouldn't start again. Battery was low. Recharged it and was able to run again, recharging about every week or so.

So the starter could have failed coincidentally, or because of the constant glow cycling?

I think I am going to go buy the only reman Bosch starter I can find in town, and give that try. If it has the same problem, I can just return it.

But I think you and Barry have it - I am thinking it is a bad starter that the McParts guys somehow were able to overcome during their bench test.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

SOLVED

Bad starter solenoid. New starter works. Still not sure how it passed the bench test.

__________________

Current Mercedes
1979 maple yellow 240D 4-speed

Gone and fondly remembered:
1980 orient red 240D 4-speed

Gone and NOT fondly remembered:
1982 Chna Blue 300TD

Other car in the stable:
2013 VW Jetta Sportwagen TDI / 6-speed MT

I had a situation where I drove my Volvo Diesel to a Relatives House and when I left there I had a normal start.
I stopped to get something to eat and when I went to Start nothing happened.

I had a Volt/Ohm Meter in the Car and the Battery showed 12 Volts.
I scrounged up some Wire to see if I could jump the Starter Solenoid and found that I barely got a spark. I moved the Wire up to the Battery and still barely got a spark.

Catty Corner a crossed the Street was an AutoZone and I bought another Battery and with that the Car Started normal.

There must have been some interior damage to the Plates of the Battery that allowed it to produce 12+ Volts but just a trickle of amperage.

So you Battery can have 12+ Volts but still be no good.

__________________
84 300D, 82 Volvo 244Gl Diesel

As I understand it, batteries are amp supplying devices that have a more or less stable voltage.

As the battery goes from fully charged to fully drained, an internal equivalent resistance can be calculated. A fully charged battery will have very low internal resistance so will supply a large amount of current. But, as the battery discharges, the internal resistance increases which limits the available maximum current output.

Your 12V reading on an, essentially, dead battery is a reflection of this effect. No load, you get 12V but put a load on it and it can't supply the current so the voltage drops waaay down.

__________________
Codifex
1981 240D ChinaBlue (Got her running with a donor engine.)
1983 300DTurbo w/sunroof.
1984 300TD manual sunroof. (Electrical Gremlins)