If the battery reads low voltage after a long drive it either doesn't hold a charge or is not getting a charge. The stock alternators do not put out full rated voltage at idle. I don't think the relay is the issue. It sounds like your car starts every morning is this correct? Is the battery soft in the morning or does it start normally. If it starts normally what was concerning you? The voltage? Me thinks you may think there is a problem when one does not exist but I've been called a pessimist more than once. You can just throw an alternator in there for fun and see if anything changes. If it doesn't help at least you can move on to something else.

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'70 F100 shortbed
'82 Diesel Westy
'83 Euro 300TD
Curtlo Viper
Yeti ARC
Surly long haul trucker

It all boils down to the type of pre glo relay you have in your car. The description you mention after starting your car matches mine exactly. I have a 96 E300d, and depending on temperature, the relay will stay engaged anywhere from 30 seconds to two minutes. I have a Scanguage attached at all times, and my voltage figures match yours to a tee. I tried to search the name you provided, but could not get any hits. Hope this helps.

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96 E300d

Yeah, if I can get 14 at idle, I don't need a new alternator. It was typical autozoo tech who was just telling me what the computer said.


The car starts every morning if I start and run it every day. If I leave it for two days (which I am doing now) It usually won't start. I have dropped the "car off" amp draw down to .13 amps. I have now left it for two days and I'm going to see what my battery volts are after two days and then see if it cranks. If I try to start it tomorrow morning and it doesn't start...its straight to autozoo for a new battery (hopefully a nice warranty covered battery).

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

Its the updated 65amp. When I bought the car it had a 55amp.


I pulled the brushes on my 55 and my 65 amp and they are both plenty long.

So I'm probably just going to delete my amp and box of 8's in the trunk permanently. that was drawing about 1/2 an amp all the time. It was nice having the low end...but I'd rather have a dependable car.


Idle rpm is about 5-6. would you suggest tightening linkage to up the rpm, or is there an idle adjust screw? I know I don't have the knob...I think those came out in 85 or 86.
Connections are nice and clean. I undid and redid the connections to be sure. Took out and inspected the regulator and brushes. They looked great.


I'll see if I can't find the part numbers on the stock relay and the afterglow relay and confirm my relay. My car should be able to handle an afterglow relay if I'm charging correctly and my battery is fresh....I typically drive about 2 hours a day on the highway. Plenty of charge time for the superdon.

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

The duration of the glow cycle is subject to a number of possible variables and is certainly not guaranteed to be exactly 35 seconds.
Only if you don't understand what it means.

sounds to me like a bad ground somewhere, maybe due to botched wiring from all the add-ons. ground is off then charging voltage will be off, couple that with other/extra loads and you have an issue...

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Current Diesels:
1981 240D (73K)
1982 300CD (169k)
1985 190D (169k)
1991 350SD (113k)
1991 350SD (206k)
1991 300D (228k)
1993 300SD (291k)
1993 300D 2.5T (338k)
1996 Dodge Ram CTD (442k)
1996 Dodge Ram CTD (265k)

Past Diesels:
1983 300D (228K)
1985 300D (233K)

I agree the 35 seconds is not set in stone, but it's NEVER 12 seconds... unless something is broken.
even understanding what the light is for is fairly useless. for the general user, it's just an indicator of glow function and a reminder to wait before hitting the starter. ya gots to wait for the full cycle on cold mornings with older motors, and generally that's 35 seconds.

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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 190D 2.5Turbo
1987 190D 2.5-5SPEED!!!

1987 300TD
1987 300TD
1994GMC 2500 6.5Turbo truck... I had to put the ladder somewhere!

Cold start glow plug light usage.

My light glows different lengths based on engine temp. Stays on almost no time if the engine is warm....stays on a really long time if its below freezing and I didn't plug my block heater in.

Is the light tied into the glow plug relay? There would have to be something that tells it to light up for a certain amount of time. It could be as simple as whether the thermostat in the coolant is open or closed...to a complete seperate engine temp sensor.

You guys talk about "those who understand it". I would like to join that club.

The "TWUTGPR" club


Botched is a very good word to describe the wiring of this car when I got it. I have since made it worse...and now...it is only slightly less worse than when I got it. But from even worse to less worse is an improvement. But I think the ground is fine. I get 14 volts at idle after I have been going a while. Fully charged battery + warm engine + low load.

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

On your model, the duration of the glow light (and the glow cycle on some timer versions) is a function of ambient air temperature at the timer. There is no engine temp input to the timer.

No. The light is controlled by a solid-state device that is part of the timer assembly. The relay itself powers only the glow plugs, when energized by the solid-state device. The light does not provide a direct indication of relay operation.

0.13 amp draw with the key off is too much and part of the problem. Start pulling fuses and see which circuit it is.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

HA! it was a .58 originally. At this point it has to be my Sony Xplod Bluetooth radio. I've been considering installing that into my 95. Looks like thats what I'll be doing.

I checked the voltage on the battery. 12.00 even...wait...12.05 after sitting for a day and a half. I don't like that either. I'll do another test with the old sony tape deck installed after I check it's off amp draw.


So.....if I lose two glow plugs will my indicator light still light up?

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77' 300D, "Cartman" SOLD @ 150K (didn't know what I had)
83' 300SD, "The Superdon" 325k+ @ 28mpg
95 E320 wagon, "Millennium Falcon" 231k+ @ 24 Mpg
95 E300D, "Sherley" 308k @ 33.69 Mpg, currently anticipating a head
99 Suzuki Intruder "Trudy" @ 45 mpg

12 V on a battery after 2 days is not good. A 0.13 amp draw should not bring it down that low in 2 days! Alternator not charging properly? Belts loose? Bad battery? Get a cig.. lighter voltmeter from Radio Shack and watch it while you drive and report the results. You should see 13 to 14 v depending on the electrical loads.

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85 300D turbo pristine w 157k when purchased 161K now
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked

I'm pretty sure you have an alternator that uses an "exciter" circuit to make the alternator charge at lower RPMs when you first start up. If that circuit isn't intact, the engine will have to be revved-up to RPMs one would normally see while driving to initiate charging. This might explain why you see normal charging voltage only after driving for a time. I also think you have a weak battery.

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-Louis

'87 300D Anthracite

Have you load tested the battery? Have you measured voltage after sitting for a day with the battery cables disconnected?

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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.

Just like every other alternator in existence.


If the field excitation circuit is not intact, no amount of revving is going to move any electrons.


You don't agree with the "afterglow" theory?