Is it my battery or the alternator??

[baker462]

hey all.. I am new to this!

here is the secnerio..

I got a 1973 280c the other day. it was running fine.

it has been running and starting fine everyday so far (about 5 days)

I drove it to work at 05:30am thursday and parked it. I just got back and when I tried to start it there was no power! (i verified that nothing was left on, lights etc...)

The weather has been cold. it was -20 to -25 (celceus) for the last 2 days here.

I got a boost, and it started right away. I turned the lights on, and heater and started to drive it.

I made it to the stop lights and had to stop. (about 1km away) when the light turned green, i accelerated, started to make my right turn, and it died!

I got another boost, and kept the heater, lights etc off and drove home fine!

when I got home and turned off the car, i tried to start it again, and there was power, but not enough to start it!

so..
would the alternator be dead?(how would I check this)
would the battery be frozen?
or is the battery just dead? (as in wont take a charge anymore)

any thaughts? where to begin trouble shooting..

Thanks in advance

[GermanStar]

Could be alternator woes, but check the battery first...

[Djenka018]

I guess it a simple thing to go to one of the battery retailers and ask them to inspect the gravity of your battery. That test will indicate batt condition and you will know for sureif replacement is needed or not.

At -25Celsius probably only very good batteries would crank for long.
Your batt may be good enough for sunny side of the world but not for Canada weather.

If batt is in decent condition than you may have problem with alternator not charging at all or not charging enough. Again, in Afrika that is a free check by same place that is seling batteries. BTW, sometimes belt that drives alternator causes poor charge (and a helluva sqweek).

[baker462]

hey all, thanks for the input.

another thing i noticed this evening was this..

when i turn the key, the battery light lights up bright red (engine not running) before actually starting the engine.

once it is started it goes out.. like it should..

if the engine is idleing, the light is VERY dimly lit (just faintly lit) if i give it some gas, it goes out completly. (untill the engine goes back down to idle)

so it seems to me that the rpm's need to be higher for the light to go out completly..

any suggestions now?

[wbain]

How old is the battery?
Is the fluid level correct?
Did the battery freeze? If so, get a new battery.
Is there any corrosion around the battery posts?
Is the top of the battery clean?
Are the wire clamps tight and clean?

[cargibbs]

From the symptoms you describe it sounds like a worn alternator. Check the belt condition and tension. Clean the battery terminals with some emery paper. Chances are you are driving around in the dark all the time with radio, heater fan, lights on and your tired alternator is not keeping up with it all.
Good luck and have a nice winter.

[ctaylor738]

Here is a post that I did on another board about this very problem. I would be it's the regulator.

Pagoda SL Forums - Alternator & Voltage Regulator Explanation

[Mercedes Benz of Florida]

If your near an Auto Zone, Discount Auto Parts or near equivalent up there in
Canada ( eh? ) they test for FREE
Alternators
Starters
Radiator Caps
Batteries

Run it to them and see what turns up
Its quick and cheap ( free )

Afterwards you'll have to see what your "wallet" says to your mind about
what to do....

Good Luck

[otm646]

Grounds, Grounds check them twice. just take a peek even if you have found your problem. compound failures are possible.