kalyna

I have a 98 chev silverado 5.7L which I am having problems with the charging system. I am on my 5th alternator in the past 18 months,
my mechanic has checked the tensioner pulley, changed the serpentine belt, checked all grounds, and changed the positive cables to the alternator and junction box, I also changed the battery. When the truck is cold the guage is showing just over 14 amps, after it warms up and I have the heater and lights on it drops down below 13.5 while idling, it will come back up to 14 when I am driving. When it drops my lights dim, so I know it's not the guage. After about 5 minutes of running the alternator gets so hot that you can hardly touch it.
My mechanic has basicaly given up, any ideas would be appreciated.
Thanks.

cardoc

Good evening
A very hot alternator is one working too hard possibly due to a bad connection somewhere in the circuit.I would first try a voltage drop test between alt, battery,engine block , chassis etc.
Hook the pos lead of volt meter to engine bock,neg lead to battery neg post bolt.With eng running,loads on volt meter should read less then 1/2 volt.Same between alt pos and battery pos post.Use meter in like fashion to ck all current paths.I'am assumming quality alternaters testing good when installed,proper rated output for vehicle,new battery tested good etc.Alternators do get hot but with-in reason.
Good luck and good night
Cardoc

qldit

Good Evening Gentlemen, it may be an idea to determine what that alternator amperage rating actually is.

I would expect the battery voltage to drop at idle like that under load conditions and increase when the engine speed is increased, but the alternator temperature is indicative of the load being excessive for some odd reason.

In some cases a defective battery can cause this, it may be worth trying yet another battery.

I would expect that alternator should be the 100 amp type but lesser amperage alternators can appear as the same profile.

Generic after-market replacements are often not the best items.

Others will have different ideas.

Cheers, qldit.

Raylo

It sounds like your voltmeter readings are normal. And the heat issue could be deceiving since these vehicles develop and maintain pretty high underhood temps. I have a 1994 Chev Z28 that gets very hot underhood and the alternator is always very hot to the touch after running awhile. But it is still the original alternator and I have never had a charging system problem. These things are hard to figure. I had a 1987 Z28 that went through 3 alternators for no apparent reason. Defective alternator design? A bad diode supplier? Who knows?

I would double check the alternator's rated capacity and maybe get a bigger one if available. Also I'd do a current reading to see if there is an unexpectedly heavy load. If so, you'd have to track it down, which could also be a challenge.

mack1

Hi kalyna,
Would you be confusing volts with amps? I haven't seen an ampmeter on a dashpanel in years and those dumb symbols are confusing. It's normal for a volt meter to show 14 volts and less when idling. The actual voltage should be 14.7 volts while charging to get current to flow backwards into the battery. You can measure this on the battery posts while idling fast.
I agree with what both cardoc and qldit posted. If you are actually pulling that much current, a wire should be getting hot somewhere. You might be able to track down the problem by feeling of the wiring harnesses.


Sorry raylo, you slipped your post in while I was making mine. I like your post also.

Hope you find a fix.
Mack1

Raylo

Agree Mack. I just assumed he said ammeter when it is really a voltmeter. The numbers are right and ammeters never had detailed scale numbers anyway. BTW, the last one I saw was on my 1966 Mustang. I kinda miss the ammeter and the car.

PilotKINW

Sounds like you may have a grounding problem - my guess is that your fuel gauge has been off a little and other anomalies have been rearing their ugly heads.

Check your firewall to cab connections (never an easy undertaking) and make sure that there is no corrosion there, the grease that the factory installs does harden and corrosion can set in. It usually begins in the tail-light connections and after a few years, works its way throughout the vehicle.

Check all of your grounds, throughout the chassis and engine compartment.

Basementgeek

PilotKINW: Hi and welcome to the forum.

I hope they got it fixed by now as this subject was started some 16 months ago.

BG