I drove the car to work yesterday, and discovered along the way that my alternator wasn't charging. The gage was only reading 10 volts.

It turned out that I lost the alternator belt somewhere, but I can fix that, no problem. What was weird is how the engine was acting when I limped it home with no alternator.

Normally my idle was 900, but without an alternator belt, I was idling at 1300 rpm's - a 400 rpm increase!! Also the engine ran cool......too cool!!

It's a 28 mile one-way trip on a 80 degree day, and the temp gage didn't get above 160 degrees! I have a 160 degree T-stat installed, but it's really weird that the fan didn't kick on even once all the way home! Normally, the fan will start before I even get halfway there.

Now, I know my battery isn't the best because I can never seem to acheive a "full charge" when I put it on my battery charger. Matter of fact, I was ready to get another one in a couple of days. I assume that the alternator was pretty much maxed out all the time trying to fully charge a battery that wouldn't take it.

But - does an alternator really take up that much power?? - Enough to change my idle by 400 rpm's and temps by 60 degrees?? FWIW, I do notice that when I set the idle, I almost have to do it with the electric fan running, because when it starts it drops my idle like 200 rpm's.

I guess what I'm asking...........does this sound normal, or do I have an electrical issue???

P.S. - Sorry, wasn't sure where to post this because it involves cooling, electrical, idle etc...

 

Judging by the lack of any responses, I guess it's normal then??

 

When I swapped out my alternator the last time I turned the car on without the voltage regulator plugged in and i got about the same simptoms as you. Then when I figured out what happened I plugged it in with the car running and I automatically heard the rpms drop to normal. I guess with the amount of parastic drag you gain by not have an alternator the engine turns faster and spins your other accessories faster aswell.

 

If your battery was already weak, you should plan on a new battery AND alternator at same time - usually a bad alternator will ruin a battery - with so much discharge and no input batteries die quickly and irreversibly.

 

The idle on my car drops a good 50 RPM when I turn on the headlights. Over 100 when I turn on the rear window defogger. About 50 from lowest to highest blower speed. Electric fan about 150 RPM.

All that stuff uses power, and the power comes from somewhere. That somewhere is the engine. Take away that load, the speed is bound to go up.

So I'd say, having no water pump and no alt, 400 RPM is probably not abnormal at all.

 

OK thanks!! It just seemed to me like it shouldn't have made that big a difference w/o the alternator belt. I still had the water pump BTW...it's also driven by the A/C belt. Good thing!

I can understand the rpm increase, but how it ran so much cooler still perplexes me.......guess I should be glad the electric fan didn't start on the way home with no belt. It may have stalled then.

I'll get a new battery tomorrow and take a closer look at the alternator.