I own a 1997 Expedition - 4.6 liter. I let it sit most of the past winter about two weeks at a time. I have been having trouble starting it. The battery is only 2 years old (Sears Gold). Although it has been sitting most of the winter I still do not think it is a bad cell but suspect the alternator. When I get it ovet 3,000 RPMs, the battery indicator light comes on. When below 3,000 RPMs, the light goes off again. Could it be that the seprentine belt is slipping at high RPMs or could it be a bad alternator? Thanks....Ed

 

Did the battery discharge while it was sitting.

A battery can freeze if the charge get low or it is allowed to go dead resulting in damage to the battery.

Are the battery terminals clean?

http://www.cdstandbypower.com/contac...t/pdf/7953.pdf

Allowing a battery to discharge without occasional boost charges can lead to sulfation...

http://www.parkeryamaha.com/index.as...on=Custom&ID=3

 

Is the battery leaking anything?

 

The battery wont cause the battery light to illuminate, if that makes any sense?
When the battery light comes on, the alternator is not functioning correctly or more appropriately, a charging system problem exists. It could be the alternator going bad or the belt slipping do to a bad tensioner or a worn out belt. Also check all your connections for tightness and corrosion. Look for the easy stuff first.

 

Thanks Tomlin, I just learned something.

 

the brushes on the rotor may be floating at the higher rpms. they are made of carbon and wear over time. the powder made by them wearing also clogs them up.
you really cant repair alternators. they are just replaced. before you do though, have it tested.

 

Thanks all. The battery is not leaking. I wil check the belt and see if the connections are tight. I guess 10 years of service is pretty good for an alternator - I will have it tested.

Ed

 

Another clue is an alternator is designed to produce power at low rpms and the engine need more electrical power at high rpms.

The old DC generators would produce less power at low rpms.

 

I understand how that works, I was thinking that if the battary was leaking that it may be a possibility that the alternator was over charging.