1982 300D-T

Same thing y'all have heard a million times before. I was having trouble keeping my battery charged, it would die after a few days.... it just wasn't getting charged. I checked my voltage regulator after I took the old alternator off and it looked fine, the things that stick out were worn but not dead. (I think it was the original alternator from 1982!).

I do take quite a few short drives, so I thought it prudent to upgrade the alternator.

Upgraded my alternator to a 120 amp model. Install went fine. Soldered new connections, checked all fuses, cleaned and checked all connections/wires from battery to alternator to starter and transmission to ground. Battery light is fine, comes on at key turn and then goes off, never comes back on. Voltage is good/same as battery at the end of the connections and at alternator when off, little blue wire to alternator shows 1.65-2 volts with key turned on but engine off. I have an upgraded Beru glow plug relay with extended glow and upgraded glow plugs, so my glow cycle takes 2 minutes or so (see below - it pulls quite a bit for the 2 minutes but switches off as it should). I have tightened my alternator belts to make sure there is no slipping. The new alternator has the same pulley as the old 55 amp model. I have done the below readings with 2 different batteries; I got an Optima even though the old Interstate was fine because the only rust on the car was a little bit under the battery - when I addressed that I wanted to get a battery that would never do it again. So I was able to try both good batteries and rule that out. With the multimeter I don't see any draws that would run the battery down by themselves...it just doesn't seem to charge enough.

My readings are below.

Off totally, battery voltage --- 12.85 volts
Initial Glow - lasts 2 minutes or so with my upgraded relay --- 12.3-12.4 volts
Idle - Glow Plug relay off, Electric Auxiliary fan off --- 13.4 volts
Auxiliary fan only --- 13.23 volts
Auxiliary fan and Radio ---- 13.2 volts
Auxiliary fan and Headlights ---- 13.1 volts
Auxiliary fan, A/C on high ---- 12.50 volts
Auxiliary fan, A/C on high, and Radio ---- 12.5 volts, maybe 12.45
Auxiliary fan, A/C on high, and Radio and Headlights --- 12.35 volts

My problem is that here in Texas the Auxiliary fan is on a lot AND I have to have the A/C on, so for the most part I'm going to be at 12.50 volts according to the readings below...which I don't think is going to cut it. However, these readings may be fine for all I know - I did not do all of them with the old alternator, these are readings done with the new 'upgraded' alternator. I have not driven the car with the new alternator for fear of having it die, so it is untested in the 'real world'.

Is there a way to charge more?? Any thoughts on how I can be above 12.5 with the things on that need to be on for my climate?

Sorry for the small novel here.
Thanks in advance, I know questions like this are tedious. And believe me, I've searched and searched the forums and can't figure out what to do. The goal is to be like some posters I have read that state they are at 14.1 volts at idle.

Best Regards,
Hugh
Austin, Texas

You want close to 14V alternator output measured at the battery posts with the car idling and no heavy loads turned on. Glow, AC, lights pull measured volts down. I've had a new out of the box Bosch voltage regulator be bad.

You want to load test your battery and bench testing the alternator. Parts store will do both tests with parts installed. Battery test conclusions will be accurate. Alternator not necessarily so unless you pull (isolate) it. One clerk insisted that my alternator was bad when the grids were pulling. Alternator that tests bad could be the regulator regardless of visual brush inspection.

I would be tempted to install a new voltage regulator instead of pulling the alt because I like having a spare regulator and easier than pulling the alternator

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

1. Is your voltmeter accurate? Try another.
2. What's the voltage at driving RPM, say 2500?
3. Is there a good ground between the alternator and chassis, and between the battery and chassis? Clean all connections, coat with dielectric grease.
4. Try a replacement battery -- it could be pulling the voltage down.
5. Where did the "new" alt come from? Not all rebuilders are created equal.

BTW - 55 A should be pretty reasonable for those cars. You're not running fuel injection or ignition systems, just accessories.

What, exactly, are you afraid is going to "die?"

Did you test the battery?

Do W123 automatics have a rear pump (which would permit roll starting the engine with dead battery)?

On mine with the Connector Removed from the Alternator and the Ignition Key on and the Engine not running I get slightly less than the Battery Voltage; not 1.65-2 Volts as you indicate from the Blue Wire. (Shown in the Pic by the Blue Arrow and Blue color.)

The Blue Wire goes to the Battery Charging indicator Light. From what I have read the Battery Charging Indicator Light Bulb needs to be 3 Watts.

When the in the Ignition switch is off I get no Voltage at the Blue Wire.

The Double Read Wires always have Full Battery Voltage.

My Alternator charges normal and I have never had a dead Battery for 4 years now. So I believe my voltage readings at the Blue Wire must be normal ones.

Attached Thumbnails

 

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84 300D, 82 Volvo 244Gl Diesel

Yes. But towing is the prescribed tactic.

First off, thank y'all so much for the suggestions, your expertise and your time.

I bought the rebuilt 120amp alt from a rebuilder in California called Eagle Electric 1. I have called him twice since and he has been extremely helpful. I still fear something is wrong with the alternator, but he is nice and if I get to the point of wanting to try another one I suspect he will work with me to get that done.

Junkman, I was trying to avoid pulling the alternator off again. I did not know the parts store could try a load test on the alternator while on the car and I'll pursue that. Even if it is not conclusive I'll give it a go. I will also have them test my battery to be sure.

I too thought of just trying a new VR, as my car does get brighter headlights when I rev the engine - I have read that that means the VR is not doing its job properly (but please correct me if I am wrong). Is the VR definitely bad if the headlights get brighter when I rev the car, or is that normal?

spdrun,

1. I have two multimeters and they both give the same readings.
2. I don't know, I will check - good idea.
3. I took every single connection in the charging system and all grounds off, cleaned it, scotch-brited it, and coated it with dielectric grease before I reinstalled it. I've also checked the end of the connections with the meters and they all read as they should except for the questionable reading at the blue wire with the key turned to the full 'on' position (but engine off).
4. I have also tried 2 batteries that are good (I have not had them tested which I will do at a parts store, but the Optima is only 3 months old and the other battery was working like a champ before I put in the Optima). I have 2-amp charged each battery for a couple of days before the tests. They both reached correct fully charged volts when I metered them after charging them.
5. See above - I wondered the same thing and can't be sure I got it from the best rebuilder, but he seems to know what he is talking about and uses only new Bosch parts and regulators on his rebuilds (for the parts that need 'rebuilding' anyway).

Diesel911, I think I had read a previous post of yours where you stated the same thing about your blue wire and that is why I put it in the original post. I was worried about mine being so low relative to yours but don't really know how to troubleshoot the low reading on the blue wire - where is it getting the 12 volts from (when the key is on)? Is it a bad connection through the cluster wiring or what? My bulb works fine, but I might replace it to be sure if you think it might help. Maybe I took my reading with the connection (blue wire to alternator post) connected and that might explain it - I will try it again with the wire unconnected to see.

tangofox007, I was afraid the battery would get low due to insufficient charging, stranding me somewhere if I drove it to a destination - low battery = not starting, which is what I meant by 'dying'. Sorry I was unclear. The 2 batteries seem perfect, but I do need to get them tested at a parts store to be sure.

Thank you all for the suggestions and ideas, I am very grateful.

Thanks agin,
Hugh

HR, where did you get the 120 amp alternator?

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the sooner you start... the sooner you'll get done If it ain't broke, don't fix it.. Its always simpler to tell the truth...
2007 Honda Accord EX
2007 Honda Accord SE V6
96 C220
97 Explorer - Found Another Home
2000 Honda Accord V6 - Found Another Home
85 300D - Found Another Home
84 300D - Found Another Home
80 300TD - Found Another Home
Previous cars:
96 Caravan
87 Camry
84 Cressida
82 Vanagon
80 Fiesta
78 Nova
Ford Cortina
Opel Kadet
68 Kombi
Contessa

I'm curious if you've made any headway. I'm also in TX, in Austin, and am having precisely the same issue. It's been a real head scratcher.

We've checked and cleaned all of the connections, tried higher amp alternators, and kept our eye on the battery's health. But the same thing keeps happening. Always in extreme weather, though.

My readings are nearly identical to yours.

Chip