the mystery continues... - PeachParts Mercedes-Benz Forum

peachykeen · #1 11-05-2011, 01:48 PM

Here's a list of things I've done to improve my cold starts on my 79 300TD high mileage wagon;

- new bosch glow plugs (noticed the difference right away)
- diesel purge last month
- religious use of power service in fuel
- new primary and secondary fuel filters
- 1 or so year old 800CCA battery
- valve adjustment pending -- hopefully this week...I know, this will help a lot...but...

After I just swapped out the glow plugs, I noticed I could now start well to about 30s F. However, I noticed that my battery drains FAST, and then just won't spin the starter fast enough. Just had this happen at 30 F this morning...battery was about wiped out from 2-3 attempts at starting...so I jumped it with my van -- glowed the plugs and immediately one crank and it started!!!

Here's my theory -- I'm either losing juice in the battery and/or the battery is never charging fully while driving? Should I replace my alternator for a bigger amp one? I've had it tested by a local electric motor tech in town and he said that the alternator tested OK, but wasn't 100% but was working...

Here's something too that I think supports my theory -- sometimes when I put a charger on the battery overnight on trickle...the battery seems to spin the starter much faster...so that's what also leads me to think that the battery that size (huge) should have no problem working well...it just isn't getting fully charged by the alternator ...or getting drained somehow...i'm a terrible electrician fyi...

Thanks again for any input!!!

sixto · #2 11-05-2011, 02:05 PM

How long/far do you drive between starts?

Sixto
87 300D

kerry · #3 11-05-2011, 02:18 PM

You need to check the state of the battery with a load test and test the output of the alternator with a multi-meter.

peachykeen · #4 11-05-2011, 02:32 PM

[QUOTE=sixto;2823109]How long/far do you drive between starts?

Thanks -- that is a good question -- sometimes it just quick 20 minute trips to the hardware store -- I know those trips don't fully charge the battery i imagine...

but sometimes, i'll be running errands...start and stop...start and stop...

maybe that might be all it is -- a lot of very short drives..and then a cold morning and the battery is weak..

peachykeen · #5 11-05-2011, 02:42 PM

Quote:

Originally Posted by kerry

You need to check the state of the battery with a load test and test the output of the alternator with a multi-meter.

Thanks -- I've had both checked at advance auto and O'Reillys -- a couple times -- battery checks out fine by both places...BUT, they both found that the alternator wasn't 100% -- but works....I'll check it again though...

if there is ANY weakness in the alternator...isn't that a sign that it could be on its way out? I'm not sure if it is a 55amp or other...what should it be putting out when running?

thanks!

kerry · #6 11-05-2011, 02:53 PM

You might have a current draw on it while it sits overnight. I'd do a load test on a cold morning before you start the car, or at least a voltage test if you don't have a load tester but load testers are cheap at HF.

peachykeen · #7 11-05-2011, 03:59 PM

Quote:

Originally Posted by kerry

You might have a current draw on it while it sits overnight. I'd do a load test on a cold morning before you start the car, or at least a voltage test if you don't have a load tester but load testers are cheap at HF.

OK -- yes, i don't have a load tester -- but I can do a voltage test...I do have a feeling there is a current draw on it --- how the heck can you track down what is doing that though if it is???

thanks!

sixto · #8 11-05-2011, 06:32 PM

Setup an ammeter and pull fuses until the draw stops or drops considerably. Then work through each consumer in the fuse circuit. In a '79 TD I'd start with the antenna.

Sixto
87 300D

layback40 · #9 11-05-2011, 06:50 PM

Quote:

Originally Posted by peachykeen

OK -- yes, i don't have a load tester -- but I can do a voltage test...I do have a feeling there is a current draw on it --- how the heck can you track down what is doing that though if it is???

thanks!

When you get home in the car & are not going out again, remove one of the battery leads. In the morning, just before you start it, replace the lead. See if it starts better. If not, its probably not something drawing down the battery.

When you were told the alt is not 100%, did they give you an explanation? Bad reg? Bad brushes?
What voltage do you have when the car has been running for say 10 minutes & the motor is above ~ 1500rpm?
What is the battery voltage in the morning before you try & start it?
How long do you crank it for to get it to start?
Let us know what improvement you get when you adjust the valves.
Are the earth strap connections clean?

hockeyboysomers · #10 11-06-2011, 12:11 AM

It might sound silly, but did you check the tension on the alternator belt. Over the years I've seen a loose belt cause these symptoms. The belt should be fairly taught, but not too tight, as that would wear the bearings on the alternator. I would check it first and then move on to other possible causes.