The Diesel Stop banner

Charging issue? Belt tensioner, perhaps?

3210 Views 15 Replies 7 Participants Last post by  Steve83
I'm unable to drive faster than 60, without the battery light coming on.

Battery voltage: 12.4 / 12.5 - Passenger / Driver side.

Not yet tested the output of the alternator.

Seems odd the alternator would/could function properly unless I race the engine, or run +/- 1900 RPM (about 60 mph), triggering the battery light to come on, as well as the voltage gauge to drop very low.

I suspect the belt tensioner is calling it quits.

Am I on the right track?
1 - 5 of 16 Posts
What does the volt meter show when the ALT light is on - and when it's off? Have you looked at the belt with the engine running, or pushed against it with the engine off? If it's slipping on the alternator, there will be an obvious buildup of black powder on the face of the alternator around the pulley; particularly on the side the belt rolls off.

But it's also worth checking the battery terminals, alternator case, alternator bracket, alternator output stud, and the wiring that runs behind the battery for damage. Click these & read the captions:

. . . .

IDK where the 7.3L block ground is, but you should find & clean it:

You should confirm the voltmeter with a DMM:

See less See more
I couldn't see any shift in the belt tracking.
It won't move fore-aft, so you wouldn't see the track shift. It's just going to slow down imperceptibly. But if it's the result of a bad tensioner, you'd see the belt going slack, or the tensioner NOT moving, or a puff of dust/smoke/rubber powder when the belt slips.
Also, the face of the alternator housing is clear of any black powdery residue.
Then look on & around the harmonic balancer. If it's slipping, you should WASH the belt & pulleys. Start with the engine off, and use a long-handled brush to get as much of the belt grooves (on the belt AND on the pulleys) as you can, using SimpleGreen/PurplePower and LOTS of water. Then start it, but skip the brush this time. :winking:

It's dangerous, but I sometimes use a wire brush on the pulleys with the engine idling if there's heavy rust or thick varnish. I don't hold the brush firmly (so my hand doesn't go with it if it gets into the belt), and I don't put my head in line with the belt (so a flying brush doesn't bounce of my skull). But I still don't recommend it. It's much safer, and only takes a little more time to drop the belt and deglaze the pulleys with the engine stopped.

See less See more
...belt..., putting the old one in the tool box.
I use a bungee cord to keep mine on the underside of the hood. If the one on the engine ever shreds, I don't have to take a step to grab the backup belt, and then get back on the road. You didn't mention if your toolbox is at home, or on the truck.
Yeah, it'd suck to open the hood & find the old belt resting on top of the engine, huh? ;)

See less See more
Neither is near the fan. They'd fall on the back of the engine.
1 - 5 of 16 Posts
This is an older thread, you may not receive a response, and could be reviving an old thread. Please consider creating a new thread.