For the last year, I've been commuting 50 miles each way to grad school. She's a '79 300td and has been dead-on reliable. It even started on the first try when it was -5 F in the dead of winter.

Since Monday, my driving habits have changed and I'm driving 14 miles each way to a new job. Now the car needs a jump to get started in the AM or after work. The battery light does not flicker at low idle either...

The battery, alt and belts are only 3 years old.

When I think about it, it did the same thing before my year of 100 miles/day of commuting. At that time, I assumed it was alternator- so replaced it. The belts and battery were done at the same time and were in need of replacement.

I wonder what's draining the battery? I don't think it's the alternator.

Here's a quick scenario. After work, car was dead. Co-worker gave me a jump and it popped over. Drove home parked in garage. An hour later, she started right up and I went to the gym. After leaving the gym 1.5 hrs later, it started. Drove 5 mins to get some food. Went in and came out 10 mins later. Car dead, so wife drove over and jumped- she popped over easily. I have the car on a charger overnight...

TIA for thoughts on this.

__________________
'07 Yukon 2500
'13 Subaru Outback 3.6R
'13 Orbea Carpe 9-speed

Currently Benzless
Formerly: 300TD, S600, E55, 560SEL

---= The forest breathes, listen.
-Native American elder

you're going to need a digital meter that reads DC current, and you will need to test a few things.
exact battery voltage before you attempt to start the car.
battery voltage as the motor is starting the car.
battery voltage as the motor is running at idle, and at a higher RPM level.

__________________
John HAUL AWAY, OR CRUSHED CARS!!! HELP ME keep the cars out of the crusher! A/C Thread
"as I ride with my a/c on... I have fond memories of sweaty oily saturdays and spewing R12 into the air. THANKS for all you do!

My drivers:
1987 190D 2.5Turbo
1987 560SL convertible
1987 190D 2.5-5SPEED!!!

1987 300TD
2005 Dodge Sprinter 2500 158"WB
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

What exactly is it doing? Nothing? Clicking? turning over slowly?

__________________
1977 300d 70k--sold 08
1985 300TD 185k+
1984 307d 126k--sold 8/03
1985 409d 65k--sold 06
1984 300SD 315k--daughter's car
1979 300SD 122k--sold 2/11
1999 Fuso FG Expedition Camper
1993 GMC Sierra 6.5 TD 4x4
1982 Bluebird Wanderlodge CAT 3208--Sold 2/13

It'll turn slow a few times, then resort to clicking. The headlights (interior dome if door is open) will dim some (dim-sum!) , but nothing dramatic.

__________________
'07 Yukon 2500
'13 Subaru Outback 3.6R
'13 Orbea Carpe 9-speed

Currently Benzless
Formerly: 300TD, S600, E55, 560SEL

---= The forest breathes, listen.
-Native American elder

I'm with VStech. I replaced the alternator in my SD with an Autozone rebuilt. It lasted about a month. They replaced it for free, but the point is -- it only lasted a month. Generally I order quality parts from this site but I skirted away on that one because of shipping (both ways - rebuilt and core). Should have bitten the bullet and ordered anyway. As VStech says, get voltage readings and repost.

__________________
John Schroader
bio burnin' 83 300D, '83 300 SD, '79 240D
"I've never met a man who was good at making excuses who was good at anything else" Ben Franklin
"You cannot permanently help a man by doing for him what he could and should do for himself" Abraham Lincoln

I would check the ground straps and clean also.

__________________
[SIGPIC] Diesel loving autocrossing grandpa Architect. 08 Dodge 3/4 ton with Cummins & six speed; I have had about 35 benzes. I have a 39 Studebaker Coupe Express pickup in which I have had installed a 617 turbo and a five speed manual.[SIGPIC]

..I also have a 427 Cobra replica with an aluminum chassis.

have you tried leaving the earth lead off the battery over night & see if starts then. This would then suggest a slow drain.

__________________
Grumpy Old Diesel Owners Club group

I no longer question authority, I annoy authority. More effect, less effort....

1967 230-6 auto parts car. rust bucket.
1980 300D now parts car 800k miles
1984 300D 500k miles
1987 250td 160k miles English import
2001 jeep turbo diesel 130k miles
1998 jeep tdi ~ followed me home. Needs a turbo.
1968 Ford F750 truck. 6-354 diesel conversion.
Other toys ~J.D.,Cat & GM ~ mainly earth moving

I had the same problem in my '79 300CD. It turned out that the battery was not a sealed unit. I pried off the caps on the battery and it was say low on fluid. I put in some distilled water and all is now well.

__________________
"Life is tough...it's even tougher if you're stupid." John Wayne


Dave
Pawleys Island, SC

'79 300CD

Thanks for the input so far.

It charged overnight and started fine this morning. Now it's sitting in the lot at work. We'll see if starts this afternoon.

__________________
'07 Yukon 2500
'13 Subaru Outback 3.6R
'13 Orbea Carpe 9-speed

Currently Benzless
Formerly: 300TD, S600, E55, 560SEL

---= The forest breathes, listen.
-Native American elder

Can you turn the alternator pully by hand? If so the alternator belt is too loose. Although it should normally squeel a little if so when taking off but not all do.

Also you should have popped one cable off the battery this morning when arriving at work. Not a good place to find you have a battery draining issue.

I was thinking the same thing re: the alt belt -- it was noisy the first AM of no-start. I'll check it.

I work in mental health, so co-workers are more than helpful. Not necessarily mechanical genuises however.

__________________
'07 Yukon 2500
'13 Subaru Outback 3.6R
'13 Orbea Carpe 9-speed

Currently Benzless
Formerly: 300TD, S600, E55, 560SEL

---= The forest breathes, listen.
-Native American elder

^ Agreed.

__________________
83 SD

84 CD

I just put an Ebay 120 amp alternator in. Very happy with the results.

Is this a good Ebay alternator for W123?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

Interesting. If it's the alt, why aren't I getting a flickering batt light?

Should it be 14v at fast idle? I can barely get it above 12v no matter how hi I rev it.

The first time it went bad, I was getting the battery light flicker. I took it to Firestone (first mistake) and they replaced the alt and battery to a tune of $800. This was November of 2006.

I had similar issues last year at this time, but I drove it so infrequently that I chocked it up to a dead battery.

Like I wrote earlier, my driving habits have changed. I was driving 100 miles/day interstate (70mph) Now it 28 miles day, mixed hwy and city driving with lights on and heat blasting.

__________________
'07 Yukon 2500
'13 Subaru Outback 3.6R
'13 Orbea Carpe 9-speed

Currently Benzless
Formerly: 300TD, S600, E55, 560SEL

---= The forest breathes, listen.
-Native American elder

Pull your voltage regulator and check the brushes...

Your alternator is not putting out enough to charge the battery, you should have at least 13.5 volts at fast idle.

However let me ask this first, what kind of glow plugs and relay are in the car? Wondering if the relay is sticking on causing the low voltage..... Just to be sure unplug the GP relay and re-check battery voltages with the motor running.

__________________
1985 300TD Turbo Euro-wagon
1979 280CE 225,200 miles
1985 300D Turbo 264,000 miles
1976 240D 190,000 miles
1979 300TD 220,000

GONE but not forgotten
1976 300D 195,300 miles
1983 300D Turbo 175,000 miles

http://i42.photobucket.com/albums/e3...e485-1-2-1.jpg