Wonder What Replacement Alternator to Get?

Hey all,

My truck has been making a really loud whining noise coming from the engine. I saw a thread on here of someone's truck making the same noise which turned out to be their alternator, so I decided to check mine today. My battery voltage is only at 12.5 with the engine running, so I'm thinking the alternator is going bad.

I was wondering if anyone has any recommendations as to where to buy a new alternator from and if it's important to buy oem or not. I'm looking at one from A-Premium right now for $150.

Thanks,

-Reece

 

Denso is the gold standard. There are other decent brands, but the cheaper ones are cheaper for a reason, especially in the last few years. Parts quality has really gone into the toilet from most aftermarket brands, even ones that were previously "good enough".

At the very least look for one locally, with a parts warranty, so you aren't out a lot.of shipping and hassle if you have to replace it two or three times until you get one that makes.it past the warranty window.

 

Check your connections first to ensure that the low voltage is not due to resistance caused by corrosion buildup. Unplug/plug alt connectors and check ground connections and battery terminals.

I replaced mine with a high output (200 amps) from bnrparts, an ebay vendor with good reviews. As long as you don't have a high draw device like fancy audio or winch, you need not worry about upgrading the wiring at this point.

Another option is to seek out an alt rebuild business. They are a dying breed but some are still out there. They can rebuild yours or sell you one they may have in stock.

 

Thank you, should I replace the battery at the same time?

 

Whatever you do do not buy one with a lifetime warranty. Companies figure they can replace those 3 to 5 times before they lose money.

 

Do you know how to tell if your truck has the 130amp or the 100amp alternator?

 

Check the main ALT Fuse, if it's 120A you have the 100 amp alternator. If it's 140A you have the 130 amp alternator.

 

Thanks, would it hurt to throw in a 130amp anyway?

 

No not really, they are the same electrically but trucks with the 100A have a smaller gauge main alternator wire and fuse so you wouldn't be able to use it to it's full potential unless you upgraded those.

 

I check my batteries with a load tester. But, to get an accurate reading, the battery needs a full charge. Your’s will not have a full charge since the alt has not been charging it fully, which is 13.5 to 14.5 volts. That being said, if the battery is 4+ years old, I would consider getting a new one. If you don't know the age of your’s, look for a sticker on the battery. It may have an alphanumeric code, like B2. That would mean the battery was made in Feb 2022. C1 would be Mar 2021, etc …

 

So if OP puts in the 130a alternator & doesn't upgrade the wires, that would be a problem, right?

 

Thank you! awesome

 

Only if you were utilizing it's full output of 130A which you really shouldn't be unless you had a completely dead battery or added alot of aftermarket electrical loads.

 

So I replaced my alternator with the 130a denso, which is what I needed, after pulling my old alternator out and getting it tested to confirm it was shot. So I was correct about that. But I started up my truck and it appeared to be charging, but as soon as I put it in reverse, the lights started flickering and the idle dropped to 500rpm, and the voltage droped from 14.4 to 12.5, any idea what would cause that? I'm, planning on replacing my battery next since its 5 years old anyway to see if that fixes anything.

 

Well, slow down. Clearly something is being greedy and drawing too much power. Have you checked all your electrical connections
Did you buy a new or rebuilt alternator? Do you have any aftermarket electronics?
What's the voltage over the battery?

 

It was a rebuilt alternator. I don't have any aftermarket electronics except a touch screen stereo interface, but I'm pretty sure the speakers are stock. The battery voltage is 12.5 with the truck off.

 

Battery sounds fine to me.
Rebuilt alternators often have the original voltage regulator which could be bad, but if the truck is fine in idle I wouldn't suspect it. Still, happens more than you think.
I can't imagine the touchscreen is drawing all that power without exploding.
Are you sure all your connections and grounds are clean and secure?
Does it only happen in reverse?

 

I cleaned the battery terminals the other day with one of those battery terminal brushes and it kinda scuffed them up, not sure if that would cause an issue? I'm sure the alternator connections are good. Just as a note, this is the same issue I was having before and the reason I replaced my alternator, it didn't just occur after replacing it.

 

No, scuffed battery terminals are fine.
Clear, I wonder if your old alternator was actually fine. Sometimes the auto stores will fake a bad reading to make a sale.
There are several other connections that might be bad causing high draw. I wouldn't be able to tell you which one. I would really check your engine bay and track your wiring harness as far as you can. If it only happens in reverse, then it's one of the components in that system.
Or I'm full of it and it's just a weird battery. Doesn't hurt to swap with your neighbor to try.

Test for parasitic drain across the battery when you shift in reverse.

 

I bet your throttle body is dirty causing a low idle and thus low charging voltage, disconnecting the battery clears learned idle so if the TB is dirty it won't idle properly until it is cleaned or it relearns which takes awhile.