Hi all,

I have a 1990 F250, 7.3L IDI diesel with ATA turbo, 4x4, long bed, supercab. Shortly after I bought the truck, I installed a battery isolator to connected to my slide-in camper - and then the
troubles started!

I am pretty competent with wiring and such, so I'm pretty sure I didn't do anything really dumb. I had a series of problems, the end result of which was I have a new alternator, regulator, and batteries.

Most of the time, the "idiot" light would be flickering, but the voltmeter seemed fine (would stay around 12V when I first started, with some movement when the preheat comes on, and would then climb to about 14V and stay there). I drove her like this for many months, with no sign that the batteries might not be charging. When I first had this problem, I took the alternator back to the shop, where they bench tested it and said it was fine.

I then had a seperate starting problem (some dirty diesel), that meant I ran the batteries down pretty low. I had a battery charger on them for a while, but I assume they were still charging pretty hard. I was driving home just after that, and I smelled a burning smell! Never a nice thing. I checked under the hood, and there was my fan belt (from engine to alternator), broken and smoking. The alternator to vaccum pump belt was still there, but was absolutely molten around the alternator pully. I managed to drive home on battery power, with a heavy brake pedal!

Has anyone heard of such a thing before? Surely normal charging by the alternator could never heat it up enough to melt fan belts??? I will pull the alternator and take it back to the shop again (it has a lifetime guarantee), but I suspect that they will stick it on their little tester again and it will look OK.

About the battery isolator, the camper connection was not hooked up when I had this problem, and I have a 40A circuit breaker just after the isolator on that link. The isolator is rated to 140A, the alternator is rated at 100A. Dual battery like all diesels.

Any advice much appreciated!

Thanks,
Chris.

 

did you touch the case of the alt to check for excessive heat? id be more inclined to look for a pully that has a dry bearing ,bob

 

Hi,

I didn't have a good look until I got home. The alt felt pretty warm, but hard to tell if it was _that_ hot. The Alternator bearing didn't seem seized, but the vacc-pump belt was most definately melted at the alternator pulley.

But you're right - it could well have been the vacc-pump bearing. Do you think an "almost seized" vacc pump bearing could have caused the alternator light? Hmmm, answering my own question, yes, I think it could, if the engine/alternator belt was slipping because of it. Hmmm, can't wait to get home now to check!

(FYI - this is a multi-belt system, the alternator has a double-pulley, with one belt to the vacc-pump, and another to the engine - I'm glad actually, it meant I could make it home, whereas if the water-pump had been involved as well, I would have been screwed...)

Thanks,
Chris.

 

It is well known that smog pumps seize up

 

Hi all,

Yup, sure enough, the vacuum pump was frozen solid! Thanks for the advice...

(btw, for those that don't know, the vacuum pump in a diesel is a little more important than a regular smog pump - it provides the vacuum for the brake booster!)

Chris.