Hot alternator..
Senior User
Joined: Sep 2004
Posts: 450
Likes: 0
From: TEXAS
Checked mine at work Friday. Truck sat all day (9 hours). Before start it was 78 degrees outside, alternator temp was 82 degrees, same as other underhood temps. Started engine--30 sec., 95 degrees/ 1 min., 105 degrees/ 90 sec., 120 degrees and stayed at 120-125 for another minutes, then cooled to 115-120 after glow plugs were off, I guess the batteries were up enough to draw less amps. I will try again Monday to make sure that these numbers are consistent. I checked at the exhaust inlet to the turbo at the end of this time and the inlet pipe was 195 degrees, idled the whole time. I will try it at 1200 RPM's also and see if that makes a difference with the alternator. Also, the alternator was very warm to the touch, but not so hot that I couldn't hold my touch it.
Senior User
Joined: Sep 2004
Posts: 450
Likes: 0
From: TEXAS
All temps are with a digital laser temp tester pointed into the inside of the alternator, not the casing or fins or edges. As far as load on the electrical system, I have a radar detector and CB radio that stay on all of the time and all of the lights were off. I put all of the windows down while the glow plugs were warming up and did not have the A/C on at all.
Last edited by me1mckee; Apr 9, 2005 at 04:57 PM.
Senior User
Joined: Apr 2004
Posts: 181
Likes: 0
From: San Diego
I have some helpfull infomation for all on this thread in regards to the Hot Alternator issue.
I told a friend of mine to let me look at his 2001 Chevy Silverado's Alternator before he started it.
It was cold, Then after he started it, It Got HOT !!
Could this be the way Alternators are on all vehicles.
Hope this helps
I told a friend of mine to let me look at his 2001 Chevy Silverado's Alternator before he started it.
It was cold, Then after he started it, It Got HOT !!
Could this be the way Alternators are on all vehicles.
Hope this helps
Thread Starter
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FTE Leadership Emeritus
Joined: Jan 2003
Posts: 161,999
Likes: 75
From: 3rd Rock
IMO it is the designing and “duty cycle” of the alternator that is causing the heat...I will still bring home a thermal heat gun on Monday to test
Remember myfordf350 when we have a situation which we are systematically looking at and figuring out…we ALL want to do it through good investigating and testing, we NEVER want to immediately say are trucks are junk and run off to the dealerships.
The level of intelligence, technical know-how is phenomenal in FTE...So all the smart guys start to diagnosis these problems calmly...they all gather data compare notes and see if further discussion is needed ....with our respective dealers...so yes add input but STAY CALM>
Case in point; many times a new person will come in and ask a question, at times the answers are short, “get it in to the dealer” then other are discussions about certain parts a sensor or …this is how we work here in FTE.
Remember myfordf350 when we have a situation which we are systematically looking at and figuring out…we ALL want to do it through good investigating and testing, we NEVER want to immediately say are trucks are junk and run off to the dealerships.
The level of intelligence, technical know-how is phenomenal in FTE...So all the smart guys start to diagnosis these problems calmly...they all gather data compare notes and see if further discussion is needed ....with our respective dealers...so yes add input but STAY CALM>
Case in point; many times a new person will come in and ask a question, at times the answers are short, “get it in to the dealer” then other are discussions about certain parts a sensor or …this is how we work here in FTE.
Post Fiend
Joined: Feb 2004
Posts: 5,378
Likes: 3
From: nebraska
Ok I just started my diesel tractor the other morning. Got off put my hands on the alternator. Very hot couldnt keep my hands on there. The alternator is just doing its job. Normal occurence. Checked again later it was cooler.
Postmaster
Joined: Jan 2003
Posts: 4,417
Likes: 3
From: Durham, NC
Yes, it's normal for an alternator to get hot. If you think about it, 12V and 100 AMPS is 1200 WATTs of power!! On some Mercedes, they have a hose
running from the back of the alternator for pulling cool air (outside the engine compartment) to cool the alternator.
running from the back of the alternator for pulling cool air (outside the engine compartment) to cool the alternator.
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FTE Leadership Emeritus
Joined: Jan 2003
Posts: 161,999
Likes: 75
From: 3rd Rock
Thanks Bob and 150ford …these posts are great for all of us......especially members like me who REALLY don't do the electrical thing 
You all have added a calming affect to my original problem and concern.
You all have added a calming affect to my original problem and concern.
Elder User
Joined: Sep 2004
Posts: 821
Likes: 1
From: Nashville
Hey Tim, I stumbled onto this alternator graph (click here) and thought you might be interested. It doesn't really answer why yours gets hot so quick, but it is fairly obvious that the things are able to handle a lot of heat. 
Also note that Ford's "130 amp" output rating is a bit on the optimistic side for most real-world performance situations.
BTW, the graph is from an alternator performance curves doc on the the Ford Body Builder site.
Also note that Ford's "130 amp" output rating is a bit on the optimistic side for most real-world performance situations.
BTW, the graph is from an alternator performance curves doc on the the Ford Body Builder site.
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