# Any Way to Extend the Life of an Alternator?



## Rick (May 10, 2002)

My 1998 Subaru Forester has a charging system problem. Advance tested it a week ago and thought the Battety was good, but that the alternator was bad as it would only boost the Batt to 13.7. 

Yesterday I tested specific gravity in the fluid and found 5 very good cells but the cell at the negative batt post was bad. It was 5 years old so I replaced it. 

I drove it a couple miles and tested voltage = only 13.7. 

2 hours and 10 miles later it was 13.4 so it seems my alternator is failing after only 110 K miles. The one the salvage yard has has 139K on it so it will be 120 to replace from the parts place.

I just wanted to be sure there is nothing -I can do - such as replacing brushes or cleaning inside the alteenator.

Any thoughts?


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## ninny (Dec 12, 2005)

Most alternators can be rebuilt. Might give it a try if you're mechanically inclined or, if not, take it to a rebuild shop. Costs a lot less than a new one.

.


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## bajiay (Apr 8, 2008)

Husband said you should buy a new one.
I know...stinks. Fuel pump is going out of my car. $240. ouch...
Good luck.


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## backwoodsman7 (Mar 22, 2007)

Rick said:


> I drove it a couple miles and tested voltage = only 13.7.
> 
> 2 hours and 10 miles later it was 13.4


13.4 is the float charge voltage for a 12v lead-acid battery, so it shouldn't be over that once the battery is recharged.

What's happening that makes you think there's a problem?


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## Rick (May 10, 2002)

Thanks to all....

BW7 - My mechanic (who is helpful in spite of his initial answer: "why should I help you keep your business away from me" - said the coil pack needs 14 to 14.2 volts from the alternator.

I guess I need to talk to a Subaru mechanic.


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## Guest (Feb 14, 2012)

A fully charged battery should put out about 13.2 volts with the engine off. You don't say if the engine was running or not when you tested the battery. When the engine is running at moderate RPMs the voltage at the battery should be 14 to 15 volts. This is the output voltage of the alternator. It needs to be higher than the voltage of the battery in order to charge it.

If your alternator is not putting out enough voltage to charge the battery then the charge in the battery will slowly go down as the engine runs. 

You can fix some things in an alternator. I had a Dodge PU that would blow a diode every time I jump started someone. Replacement meant removing the alternator, disassembling it, checking the diodes, and replacing the bad one. A new diode only cost a few dollars but replacing it was a pain. If you have a multimeter, you can check a diode. A diode only allows current to flow in one direction. If you test for impedence (ohms), a good diode will have little impedence in one direction and lots in the other. A bad diode will have little in both directions.


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## backwoodsman7 (Mar 22, 2007)

Nimrod said:


> A fully charged battery should put out about 13.2 volts with the engine off.


Only if the engine was just shut off. A fully charged 12v battery is about 12.6v, and that's what it should read after it's sat a little while.



> When the engine is running at moderate RPMs the voltage at the battery should be 14 to 15 volts.


If the battery is charging, yes. After the battery is fully recharged, if the voltage at the battery is higher than its float charge voltage, it's being overcharged. For a 12v car battery, that's 13.4v - 13.5v.


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## Bluecometk (Jun 20, 2009)

Your 1998 Subaru with a new charged/satisfied battery will have a running voltage of between 13.6 and 14.2 volts at 2200 engine rpm on a 70degree battery temp with all systems off. Subaru Denso Alts are known to ware out the brushes at about the 140,000-mile mark. Subaru Nippon Alts go at about the same mileage but the bridge rectifier goes from excessive heat. With those you may see the brake light on the dash start to light for no reason due two the unique brake light checking system in them. In some instances an unusual phenomenon will occur. With the engine idling, the DS door open and the window lowered with the auto down option, the window will continue to cycle to the down mode. When this happens you can see the door area flex from this occurrence. Using an A/C volt meter across the Pos and Neg terminals will show .04+ A/C volts and this intern will Show/require the need for the Alt to be rebuilt or replaced.

As a note your alt should be able to put out about 112 amps to about 124amps at 2500 engine rpm and full field with a voltage just below 10.6Volts.

As another side note A Subaru alt will run at 324 to 340+ degrees Fahrenheit at full field. They will do this for about 3.5 hours before the solid-state internals start to fail. The reason for this added info is that heat produced from poor battery condition and high mileage is probably your cause for the failure.
Sometimes the Bat wire conductor will be discolored and the insulation will be brittle and decayed. Subaru Alts are grounded through the case and mounting points. Providing a second ground path to the ground straps on the block can also improve alt performance and longevity.

Note some dealers may still have rebuild parts available. Subaru also has an OE remanufacture program and they are fairly reasonable. 

These are just my opinions, hope they help. 

Bluecometk


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## foxtrapper (Dec 23, 2003)

Your mechanic is less than impressive if they are making a claim of a coil pack needing 14-14.2 volts.

The voltage you're seeing 13+ is a little low, but not impossibly low. Many a modern alternator puts out rather low voltage, and does the job just fine for the system. It's the older alternators that tend to put out 14-16 volts, regardless of how they boil the battery. More modern ones tend to put out just enough to do the job, and no more.

Just so you know, many times the test done on the alternator by a parts store will show a pass when the alternator has a bad diode or two, and is not producing the charge it should.

Your alternator can be rebuilt, and you can do it. Don't simply throw a handful of parts at it, identify what is defective and worn, and replace those parts. Generally, the cost of this will be every bit as much as simply buying a rebuilt alternator. But at least you can say you did it. http://www.nationsautoelectric.com/index.html is a good place to start with for pricing the components for your alternator.


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## Esteban29304 (Apr 29, 2003)

The alternators you get from these " discount-type stores " are patched & NOT fully rebuilt. Take it to a place that rebuilds them.


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## cmcon=7 (Mar 7, 2010)

I replaced the brushes once and fixed it, didn't even need to remove it from the vehicle.


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## Danaus29 (Sep 12, 2005)

110 k miles on the alt and you're surprised that it's failing, maybe? We just replaced the one in the van this summer, less than 100 k miles and it was shot. Bought a lifetime guaranteed one, spend close to $200. Won't need to buy another one as long as we own the van and O'Reilly's carries that brand.

You can rebuild them. Takes some time.


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## Darren (May 10, 2002)

Bluecometk said:


> ...
> 
> As another side note A Subaru alt will run at 324 to 340+ degrees Fahrenheit at full field. They will do this for about 3.5 hours before the solid-state internals start to fail.* The reason for this added info is that heat produced from poor battery condition and high mileage is probably your cause for the failure.*
> Sometimes the Bat wire conductor will be discolored and the insulation will be brittle and decayed. Subaru Alts are grounded through the case and mounting points. Providing a second ground path to the ground straps on the block can also improve alt performance and longevity.
> ...


What BluecometK said and:

If you want to get the longest life out of an alternator don't allow the battery to discharge too much. In oher words if you run a battery all the way down, use a charger to fully charge it rather than partially charge it and use the alternator to finish charging it. If you get a jump start someplace to get home, again use a charger to fully charge the battery when you get home. Alternators aren't designed to fully charge discharged batteries repeatedly. 

Check your battery periodically for the amount of charge. When you know you have a weak cell, get a new battery to protect your alternator. Sometimes one of the desulphation units will restore the battery.


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## Rick (May 10, 2002)

Thanks for the tips, warnings explanations and perspectives.

I only use it twice a month. I guess I'll have to run it more often or keep it charged.


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## Darren (May 10, 2002)

In winter I remove a bunch of batteries, haul them to the barn and start checking them. I use a hydrometer to check the cells, a battery minder to alternately keep the charge up on them, and a battery desulphator to check voltage level and try a bit of restoration.

The battery minders work well.


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## Rick (May 10, 2002)

We have no grid tied electric - that equipment works best with grid electric, doesn't it?

Otherwise that's what I'd do.


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## GoldenCityMuse (Apr 15, 2009)

Well, just hook up a PV panel with charge controller to your battery.


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## Darren (May 10, 2002)

Rick said:


> We have no grid tied electric - that equipment works best with grid electric, doesn't it?
> 
> Otherwise that's what I'd do.


They sell a version with either 5 or 15 watt solar panels. You should be able to adapt it.


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## foxtrapper (Dec 23, 2003)

Rick said:


> I only use it twice a month. I guess I'll have to run it more often or keep it charged.


Running it twice a month is more than sufficient.


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## Rick (May 10, 2002)

foxtrapper said:


> Running it twice a month is more than sufficient.


thanks for the thought. I picked up a 100K, 1990 Ranger PU, and after 2 weeks idle she started like a champ.


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## travis91 (Jul 26, 2005)

off topic but you mechanic sounds like a -----hole.. might be time to find a new one..


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