Ok, I have a completely stock Ford Alternator. It looks to be from the mid to early 80's....How many amps should it be putting out? I find that as long as I dont run my electric fan, I'm doing just fine....but if I have the fan running, the battery is toast......Would a 60 amp alt do the trick? Or should I go with a 75 amp?

 

Ford had many different alternator outputs, so it's going to be hard to determine. If it's from the 80's, I would not think it is any lower than 55 or 60 already.

What you need to look at is the belt tension and the idle speed. You really do not need the fan unless you are idling and going slow around town. Going down the highway provides enough airflow for cooling. So we need to look at the times when it is needed.

Idling in hot weather is where it's going to get tough. Most manufacturers realize this, especially if you are running air conditioning. So most cars and truck increase the idle speed when the ac is on to help with cooling, to turn the compressor faster, and also help the alternator keep up. Even if you installed a 100 amp alternator, you will never see any increase in output if the alternator is not turning sufficient rpms.

 

I will know for sure what RPM it is idling at in about a week. Thats when I will be getting my Tach in the mail. However, it SEEMS to be idling around 900-1000 RPM. That should be MORE than enough to keep it going I would think. I went to the local parts store (schucks) to see if they could test the thing on the truck, but the kid told me that iif I couldnt start it, they couldnt test it. I told him that it was fine to start, but it might not start right this minute because it was warmed up and the fans had been running, so the battery might be low. He said (this is funny) If the alternator was not working right, the truck wouldnt run. I had a good laugh at that one, and tried to educate him a bit about how the battery will keep it running for a while longer after the alt goes out and that the battery will recharge it's self overnight if it wasnt too far gone....He wouldnt listen to me. His loss. I still have to get it tested though. The majority of my driving is around town and traffic here can be a REAL bear.....Seattle traffic is some of the worst in the nation next to new york and LA.

P.S. I put on a volt gauge, but it is only reading 12 volts where it is located. When I hooked it up to the battery direct, it read around 12.5 - 13.

 

I was going to say you can check it yourself. Read the voltage on the battery with the truck off. Then read it with the truck running. The voltage should be higher with the truck running. That means it's charging.

Then read the voltage with the fans on. If it drops below 12, you are draining the battery.

And I would think you should be able to get about 13.8v with the truck running and the fans off.

Do a little testing and see what you get.