Alternator or Battery or ????

[Mart]

I just replaced the battery and the alternator, both with new GM units.

On my drive to work today the volt reading was 13.5 all the way, until I got off the highwaythen it went down to 13.3, by the time I got parked it said 13.0.

What else could this be, I know that when things are hot the voltage might be lower but this is wierd. And things are hot in Toronto right now (34Celsius of 94 F)

I was thinking maybe the belt or tensioner, I know the tensioner is close to the limits, and when I replaced the alternator the pulley was a slight bit smaller than the one on it.

Is there anything else electrically that I should check. The car sat for a week after replacing the battery and did not lose a volt.

HEEEEELP

 

[WhalePirot]

Does your car have the underdrive pulleys? Some sets include an alternator pulley to keep the unit spinning fast enough at idle.
I am not sure you have a problem, yet.

 

[Mart]

The new alternator actually has a smaller pulley the the old one did, which would explain why the tensioner is looser.

Do those sets usually have a larger Alt pulley?

 

[WhalePirot]

I don't think there is a 'usual' with kits. If I were to opt for a set (which I won't) I'd also choose to get the alternator pulley.

A smaller drive (crank) pulley turns all the accessories slower, lowering the output of the alternator, power steering, etc. The only way to increase alternator output is to also mount a smaller pulley (or rev the engine), assuming the voltage regulator is okay.


edited for a boo-boo. :confused I think I need more sleep. I apologize.

 

[Mart]

Thanks alot WhalePirot, I think I'll change the pulley.

I have a new tensioner coming tomorrow and I believe the heat is affecting the belt with the old tensioner.

This afternoon I got into the car to come home from work and fearing the worst, thinking she would be dead or really rough because of the low voltage, she fired right up and got up to 13.8 on the way home.

I just hate worrying about things so replacing them is a comfort.

Thanks
Mart

 

[jiangtao]

I have a question about the tensioner. If it might be going bad would it make a noise? I have noticed the past few days a noise {can't describe} coming from up front. I have also noticed that my volt reading is about 13.7-13.5. Before, it was 14.1-14.2. It hasn't been any hotter than when I first noticed the noise than before. Thanks!

 

[G Winter]

I have two 1989 Rivieras. We are having hot weather as of late and have notice that the voltage on both cars drops after they are driven for awhile. After setting for half hr or more most of the time the voltage is back up. The voltage is normally about 14.2 ,when hot it goes down to the high 13s . Anything electrical is not as efficent when hot if I remember my electronics correctly. Also , once an alternator gets to a certain rpm which isn't that high the output don't change much. An altenator puts out full capacity at quite a low rpm. With the smaller pulley on the altenator It will turn higher rpm. Belt slipage could be a factor, but it takes a lot to make a serpentine belt slip.

 

[WhalePirot]

I believe the heat is affecting the belt with the old tensioner.

Ummm, I'm not sure I buy this.

she fired right up and got up to 13.8 on the way home.

That should indicate battery charging.

I have a question about the tensioner. If it might be going bad would it make a noise?

The pulley on it might.

I have noticed that my volt reading is about 13.7-13.5. Before, it was 14.1-14.2.

This is more a function of battery charge and system electrical load level than temperature. I do not know if the voltage regulation includes alternator temperature, which might be reduced on hot days, to protect the unit. Maybe C4C5 Specialist or another knows. The voltage should reduce as the battery gets more fully charged, while driving. There is a LOT of excellent info on this under older threads. SEARCH, SEARCH.

 

[tyrel]

I would not place too much reliance on the voltage readout, for some reason they are sometimes inaccurate. In fact, the service manual for my car suggests replacing the entire dash display if the voltage reading is inaccurate!

If the car is otherwise running okay, I wouldn't worry about it, because charging problems will manifest themselves pretty quickly. If you're really worried, a digital voltmeter is $20 at Home Despot or SLowes or Radio Shark, you can test the system yourself and get a much more accurate number.

 

[tyrel]

I have a question about the tensioner. If it might be going bad would it make a noise? I have noticed the past few days a noise {can't describe} coming from up front. I have also noticed that my volt reading is about 13.7-13.5. Before, it was 14.1-14.2. It hasn't been any hotter than when I first noticed the noise than before. Thanks!

Anything with a bearing in it has the potential of going bad. Any mechanic can diagnose bearings with a stethoscope, you can do it too, they are cheap and Sears has them in stock. Best money I ever spent. Just remove the serpentine belt and listen to each belt-driven accessory, if it catches or grinds, bingo there's your bad bearing. The stethoscope comes in handy for so many weird noises on the car.

 

[Mart]

Well I replaced the whole idler arm and pulley, things seem much quieter and smoother now, After all of the reading done many people say the bolt holding the tensioner on is a different thread, not so on mine and it looks original.

It took about 15minutes to replace.

Oh well everything seems good now.

Thanks guys
Mart

 

[Mad-Mic]

i run a crank pulley only, stock alt pulley. my theory is i wanna make horsepower and if i'm overdriving something that i'm trying to underdrive in order to scavage more of that parasitic horsepower is defeating the purpose. so in that respect i get a best of 13.7 above 1000 rpm and at idle 12.7 volts or so. been running like this for a year now but between this time i have lost a replaced AC Delco atlinator that failed at 40k miles and i also lost a batter that had unknown miles on it. if memory serves me right i think the paperwork on the battery was either 95 or 97 so it was old too. 10k miles later autozone lifetime warrenty altinator and a red top optima in it's place and she's good to go.

rule of thumb. you don't have a problem unless your voltage drops below 13.2 under engine load. at 1000 rpm and more your altinator is charging. your car is firing off thousands and thousands of amps and needs an energy sourse other than the batter so the altinator is always charging about 1000 rpm. if the drop happens slow then it is the altinator. if it won't start it's the battery. easy to figure out