Alternator Overheating?

[jacob dehart]

Ive got a 94 k1500 silverado 5.7 tbi. I have been going behind previous owner with wiring. It is a bit hectic. Most everything works and functions to my knowledge except for the overhead interior light but not too worried about that, and the fuel gauge . Ive had to fix dimmer switch and I deleted aftermarket lights and a trailer break. I have fixed a couple of miscellaneous shorts as well. After doing so i finally got 14.5-15 steady volts on the dash, 14.6 to the battery, junction block, and alternator. Before it would vary from 12-15v. And all of my fuses are good and am getting power to whole fuse block.

*After doing these things i have realized my alternator will overheat, hot to the touch in 5-15 mins.* It is brand new, oe alternator. I do not know why. My best guess is there are shorts I have not found or the previous owner really messed something up i haven't found. If anyone has any tips or what to do going forward, it would be a big help.

 

[Schurkey]

Define "hot".

Put an infrared thermometer on it, or any other sort of thermometer you could rig up.

Wild Guess: Perfectly normal, other than your voltage seems a bit high.

 

[Komet]

Last time I had an alternator get hot (as in, too hot to touch, burny smell, visible heat damage), it was a bad alternator.

If the vehicle was doing something to the alternator to make it hot, I would assume it's working very hard, which means I would expect to see excessive amp draw. How many amps is the vehicle trying to pull from the battery with key off?

 

[jacob dehart]

Key off, battery rests at 12.6 volts.

Last time I had an alternator get hot (as in, too hot to touch, burny smell, visible heat damage), it was a bad alternator.

If the vehicle was doing something to the alternator to make it hot, I would assume it's working very hard, which means I would expect to see excessive amp draw. How many amps is the vehicle trying to pull from the battery with key off?

Define "hot".

Put an infrared thermometer on it, or any other sort of thermometer you could rig up.

Wild Guess: Perfectly normal, other than your voltage seems a bit high.

Sometimes takes 5 minutes other times takes 15. Hot as in above normal operating temp for the alternator. Too hot to keep my hand on for more than a couple seconds.

 

[RichLo]

I would run an ammeter on the alternator to get some real numbers on what its doing.

I keep one of these in my toolbox for diagnostic uses like this situation

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[Komet]

Key off, battery rests at 12.6 volts.

We are looking for amp draw, not voltage.

 

[jacob dehart]

With the key off amps read .03 In run position .03. While running .04

 

[Road Trip]

Ive got a 94 k1500 silverado 5.7 tbi. I have been going behind previous owner with wiring. It is a bit hectic. Most everything works and functions to my knowledge except for the overhead interior light but not too worried about that, and the fuel gauge . Ive had to fix dimmer switch and I deleted aftermarket lights and a trailer break. I have fixed a couple of miscellaneous shorts as well. After doing so i finally got 14.5-15 steady volts on the dash, 14.6 to the battery, junction block, and alternator. Before it would vary from 12-15v. And all of my fuses are good and am getting power to whole fuse block.

*After doing these things i have realized my alternator will overheat, hot to the touch in 5-15 mins.* It is brand new, oe alternator. I do not know why. My best guess is there are shorts I have not found or the previous owner really messed something up i haven't found. If anyone has any tips or what to do going forward, it would be a big help.

Welcome to the GMT400 forum! Always nice to have another enthusiast join the old truck cadre.

In order to get a better feel for what's going on, we need a little more detail about your electrical system.

Does your truck have only stock electrical loads, no options? Or are there one or more high wattage audio amps,
+ healthy bank of off-road Daylighters, etc? Aftermarket electric cooling fans? What is the state of your battery?
Will it pass a load test? Do you drive the truck every day, or is it mostly a weekend toy?

I've worked with high power electronics, and while troubleshooting wondered exactly what temp something that
was 'too hot to touch' would register on a thermometer? I would have guessed ~120° F, but according to NASA
the average is actually ~110-112° F. (NASA study for Astronauts)

I fully get that a healthy alternator working into a stock electrical load while cruising down the interstate on a 70° day
should be touchable. But I can easily see a healthy alternator working into high amperage aftermarket loads getting
hotter than I can touch yet still working within it's design limits. (They have to, underhood temps down south are
much higher than what we're talking about here.)

Let us know what kind of electrical setup you've got going on, and we can give you a better guess...

 

[RichLo]

With the key off amps read .03 In run position .03. While running .04

Thats not measuring alternator output, just static amp draw.

You need to unhook your alternator output and put a HIGH AMP ammeter between the wire and the output stud. DO NOT use your multimeter, they usually have a 10 amp fuse and you will blow that right away. That link that I put above is 60 amp and can go higher for short periods of time for diagnostic purposes. Just wire up some short leads so you can secure it to the output stud on one end and the output wire on the other. And obviously unhook the battery when your doing this as it'll be constant hot and tape up the leads well so when the engine is running they wont shake and spark on something.

 

[GoToGuy]

Have you ever felt a generator or alternator running at full load? There making energy and other devices want that energy. A byproduct is heat. Everything under hood is hot. The engine and other parts don't operate at comfortable temperature for you. They operate at what's normal for them.
Water temp 195°. Oil temp the same or less. Transmission fluid the same or less. Alternator/ Generator producing volts and amps , the speed and muscle of electricity, heat. So if it does not make unusual noise, no smoke, has good voltage, and check with amp clamp, and looks good with everything on at 2000 rpm. Sign it off, send it out. That's what I would do, your results may vary with use.