I have been noticing my voltage being on the high side when first starting my car up. It is usally around 15 to 15.5 then settles down to 14.5 once the engine is warmed up. Is this normal or is my alternator starting to die. I have 69k on the car and am still on the original alternator.
Thanks
Tony

 

If your gauge is correct, 15 or higher is too high. Optimum is 13.8 - 14.2. I'd use a digital multimeter to check the voltage. It's possible that your alt. can be going but before I'd get rid of it, check the voltage with the meter to confirm.

 

Mine does the same. Sometimes, the needle on the gauge flickers back and forth between 12 and 16 (and the backlights on all the instrumentation, most noticeably on the digital display, fade in and out in sync with the needle jumping back and forth). I might go to autozone and see if they can check it for free. I think they can do that. C4 alternators look extremely easy to change. Are they? I haven't tried-there may be something I don't know.

 

Hi all. Yes the alternator is fairly easy to change. The one tricky part is belt tensioning. Get yourself a belt tensioning tool (the one I have is fairly long with a kind of y shape on each end with a hex barrel nut in the middle). I put the tensioner between two pulleys and then slowly adjust the body of the tensioning tool with an open end wrench. I am sure there are other ways to tension the belt properly and get the alternator bolted down but this works best for me on my 87.

 

Sounds almost perfectly normal. Are you getting these readings off your digital gauge? Normal is 13.8 to 14.2, a tad higher right after engine start is nothing to worry about. I rather doubt you need to do anything other than drive it.

 

Check for a loose or corroded battery cable.

 

I recently tightened a loose battery terminal on an 87 buick, and the voltage at the battery terminals dropped 1/2 volt.

Reason is that the alternator/regulator does not receive proper voltage feedback from the battery, so it 'thinks' it needs to increase the voltage.

So, chances are your alternator/regulator is fine (unless you ignore this problem too long).

Also, have the battery tested, and if it is 3 years or more old, consider replacing it. Older batteries, especially ones that have been allowed to fully discharge a couple of times or have remained at a partially discharged state for extended periods, will build up sulfate on the plates, which reduce their effectiveness as well as causing the alternator/regulator to increase voltage during recharge.

Also, if you do not drive the car regularly, consider a battery tender. It will extend the life of the battery and save your alternator/regulator by reducing how much amperage it must generate (and associated heat/wear & tear) to recharge a partially charged battery.

Our cars have a small parasitic (constant) batttery drain, which can be larger if there are problems in the electrical systems.

Also all batteries have their own self-discharge rates, which further contribute to a strain on the alternator if the car is not driven frequently.

Lastly, if replacing the battery, all batteries are not the same. A true 'maintenance free' battery (what most of our cars came with) has a slightly different chemistry and require a slightly higher charging voltage which matches our alternator/regulator.

This slightly higher voltage can shorten the life of regular batteries, so consider a few dollars spent now can be worth it in the long run.

 

GM says alternator output voltage can be as high as 16 volts and be in specifications. Your 15 volts upon startup won't harm anything although it is on the high side. More normally the alternator output voltage is 14.7 volts cold which drops to 13.7 volts hot. To see if your dash voltmeter is correct, I would measure the voltage at the battery terminals, engine running and compare it to the dash voltmeter. The dash voltmeter measures the voltage after the ignition switch and there is normally 0.3 volts drop across the ignition switch terminals, so the dash voltmeter will be 0.3 volts lower than the battery terminal voltage.