01 Blazer alternator overheating w/good alt
 

Hi guys, I need of some help.

Here's the deal, I have a 2001 Blazer 4x4, 4.3 vortec with the z71 lift. No aftermarket stereo or anything. The block is from a 97 but using all other components from the 01. My alternator is overheating within minutes of starting. Its the third one and each has been tested. They have passed test for regulator, diodes and output at my local auto parts stores. The battery is 6 months old and has 12.6volts. The alternator runs at an average of 14.5 volts and under full load (everything on) 12.6volts. I have a voltage drop of .14volts on the negative side, all the grounds were cleaned and check for continuity .001. The belt and tensioner are new. The truck idles at 650 rpms. I have a known short with my courtesy lights but the fuse is removed, oddly enough it disengages my 4x4 switch on the dash. The truck is severely underpowered despite a full tune up, new iridium plugs, wires, fuel filter, pcv, dist cap, rotor, ign coil, air filter, oxygen sensors, and fuel injection cleaner. Getting 55 psi from the fuel pump but drops to 50ish while driving.

Any ideas on what's left to check, or a place to get started would be helpful.

Thanks,
Ken

How do you know it is overheating? Does it start smoking? How hot does the battery get. I think you are on to something when you say you are down to 12.6v with everything on? Does this include rear defroster?

If it doesnt, the output should be closer to 13.5v at idle with all your stuff running. There has to be some type of electrical component pulling a big draw on your electrical system.

Just short of me knowing how you know the alternator is overheating, I will say that an alternator usually gets scalding hot to the touch when it is on, due to the radiation of heat in your engine bay, and the internal windings themselves are also creating large amounts of heat.

Fuel pressure while running doesn't mean much. What is the pressure with the key in the run position and the engine off? It should be 60-65 and not drop below 55 psi after 10 minutes.

are you running the belt to tight ?

The belt is not to tight, its not smoking, just overheating. The alternator is running up temps up over 160+ degrees within 5 min's. An alternator should get hot progressively and you should still be able to touch it after its been running. I have been using a thermometer to check the alternator housing temp. I connected an amp meter and found that the amp draw is at 60 amps when starting. When the car runs for 2 min's and drops to 40 amps and stays. From what I understand, the truck should be running at less then 10 amps. Can anyone confirm that?

However none of the fuses have blown. With the car running and the amp meter connected I pulled the fuses and relays one at a time with no drop in the amp draw.

Fuel pressure is not really my problem just tried to give all the info I could.

12.6v is with everything running; Rear defrost, A/C, high beams, radio, wipers, etc. Anything I could turn on that uses electricity.

have you bench tested the battery? If the battery is failing in any way it puts extra stress on alternator, electric components are funny like that. If all good there double check charging system, not unheard of to get defective alternators and in fact many chain parts stores like Advance or Autozone offer free checks of both above mentioned. good luck and update us!

Three different alternators with the same issue. They have been bench tested along with the battery. The battery was replaced anyway. Is there a way to do an amp draw test on a starter that is not connected to the truck? I disconnected the battery completely and the amp draw did not drop. I have removed each fuse (one at a time) from both fuse boxes and still no drop. At this point I'm going to start disconnecting electrical systems, one at a time.

wow...even pulling each fuse at a time? hmmm the only component I can think of not through the fuse box is the starter. Or any after market amp? Followed main positive cable all the way through to make sure it's solid? Same with ground wire? Ohm them out even.... too much resistance will make more heat... loose connections on either terminals or to fuse box or chassis ground bolts..

Just throwing all types of possibilities I can come up with....

Have you owned the vehicle since new? If not has this problem been with it since you have owned it? Did it start this after any repairs of any kind? Just collecting info to try and help.

BTW
I remember being told that GM was not close to their under hood temp specs

I also know of garages that replace both the battery and alternator if either fails