Starting issues
 

This is on the 1980 300 cd 617 n/a
Car is the daily driver and needs to go every day.
Lately I have been having a strange starting issue.

Problem:
Lately the car has been turning over real slow. I mean like 6v tractor slow or timing way advanced on a big block slow. The kind of slow you get before the battery starts clicking. But it still somehow starts. Runs fine after starting.

Block heater plugged in and works fine
Glows work fine test fine
New Bosch battery last march
Battery before starting sits at 12.3 volts
Battery with car running and no accessories on is at 13.7 volts
Battery cables are tight

Other observations:
The other night on a long trip the headlights seemed dim. If I turned off the heater blower they got noticeably brighter. Sometimes the heater seems to blow better then others on the same settings. Which had me thinking alt or voltage regulated but I can't consistently replicate the conditions.

Also the car had been starting strong but seems to do this slow thing when it snows. I am thinking maybe moisture from the snow has something to do with it??


Any help would be great my brother already hates this car the last thing I need is for it to leave him stuck at work. My guess is starter or some real weird electrical gremlins. Anything common come to mind?

Recommend you have a load test done on your battery. A load test simulates the effect on the battery by the engine being cranked. Any good auto parts store, independent repair shop, Pep Boys, Sears Automotive will be able to do this. A load test can also be performed on the starter.

12.3v is a bit low for the battery with the car off, and anything under 14v is low for the car running. Seconding having the battery tested for free at a parts store.

Twelve point three volts with car off is too low. First check is to reach Down and see if you can turn the alternator fan blades by hand. If you can the belt is too loose.

Good point about the alternator belt (s). If they are properly tensioned then while the battery is being tested have the alternator output tested also.

How did I miss this! Yup the belt is loose I will tighten it and see what happens. Not going to call it "fixed" but this could definably be it!

Thanks

Actually depending on which one of the Mercedes Manuals you read a good charging rate can be as low as 13.3 Volts another has it as 13.4 Volts.

What I would think would be revealing is to unplug the Glow Plug Connector that Goes to the Ignition Switch at the Glow Plug Relay (you need to remove that particular connector because otherwise while the Starter is cranking the Glow Plug Relay is on) and put your Volt Meter probes on the Battery Terminal and see what the Voltage drop is when you first start to crank.

Recharge the Battery and do the same with the Glow Plug Connector back on and again whach to see what the Voltage drop is.

You also cannot discount that it could be the Starter itself if the Battery turns out to be OK.

Metal shrinks when its cold. I would replace the starter with one from a turbo, if the brushes are very worn, when it cold and the metal has shrunk...they may not be making good contact...then the old grease in the starter turns to a rock when its cold. I would also install thicker gauge cables. And as was said have the battery tested.