Alternator Overcharging on a 2018 GT Premium

[shadow1966]

I've just recently bought a used GT (used to drive the ecoboost) and have been noticing the car cranks for a bit before finally starting up. I've put the battery on a trickle charger and noticed no improvement.

I took the car to autozone and they said my battery was fine (Just uncharged) but that my alternator was running a bit hot. Is this a common problem for a GT and/or worth replacing?

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[Boosted Pony]

Has the battery ever been replaced? If so I bet who ever replaced it did not reset the BMS Battery Monitor System which will cause issues with a new battery. I just replaced the battery in my 2021 2.3 HPP Mustang as a preventive measure and I used my Autel scanner to reset the BMS system.

You can reset it with out a scanner, just do a search on the web how to reset Ford Mustang BMS system, it is not hard to do, just print the instruction and follow them, it only takes a minute or so from start to finish. If it does not work the first time try it again, you might have taken too long on one of the steps.

 

[ORRadtech]

What exactly is "a bit hot"?
The alternator should output 14.2V +/- a couple of tenths. It can go higher or lower though depending on if the battery monitor believes the battery/car needs it.
If the parts store said the battery charge is low then you need to charge it with a dedicated battery charger. The alternator is not designed to completely recharge a dead or very low battery. Its purpose is to provide power to operate a running car and replenish what the starter used to start the car. A trickle charger may, or may not, fully charge a battery depending on the charger output and the amount of time it's connected. A low output and overnight probably won't be enough to fully charge the battery.
In short, it's too early, and not enough information, to tell if anything is wrong (besides the low charge) or anything needs replaced.

 

[shadow1966]

What exactly is "a bit hot"?
The alternator should output 14.2V +/- a couple of tenths. It can go higher or lower though depending on if the battery monitor believes the battery/car needs it.
If the parts store said the battery charge is low then you need to charge it with a dedicated battery charger. The alternator is not designed to completely recharge a dead or very low battery. Its purpose is to provide power to operate a running car and replenish what the starter used to start the car. A trickle charger may, or may not, fully charge a battery depending on the charger output and the amount of time it's connected. A low output and overnight probably won't be enough to fully charge the battery.
In short, it's too early, and not enough information, to tell if anything is wrong (besides the low charge) or anything needs replaced.

I'm not entirely sure, I never asked the exact alternator output when they ran the test.

As for the trickle charger, thanks for the advice I'll probably try that out if I continue to have problems.

 

[ralph7]

Has the battery ever been replaced? If so I bet who ever replaced it did not reset the BMS Battery Monitor System which will cause issues with a new battery. I just replaced the battery in my 2021 2.3 HPP Mustang as a preventive measure and I used my Autel scanner to reset the BMS system.

You can reset it with out a scanner, just do a search on the web how to reset Ford Mustang BMS system, it is not hard to do, just print the instruction and follow them, it only takes a minute or so from start to finish. If it does not work the first time try it again, you might have taken too long on one of the steps.

Doesn't the BMS reset itself after a few hours?

 

[PoCoBob]

Doesn't the BMS reset itself after a few hours?

I changed the battery in mine last year and did nothing except what the owners manual said to do. Let it idle for a couple minutes and then take it for a 10 mile drive. Then let it sit for a minimum of 8 hours with the doors locked. I have no issues after doing that, the BMS reset is for the dealer who changes a customers battery and doesn't want to tell the customer to do the things I listed. And while it was idling I reset the power windows bounce as well. That was noted in the manual to do after a battery change.

 

[SnowFox]

I took the car to autozone and they said my battery was fine (Just uncharged) but that my alternator was running a bit hot. Is this a common problem.

What was he doing when he said that?

The alternator. Assuming you just stopped at the store should be a bit hot. Along with most things in the engine bay. (Obviously)

Output voltage? Like noted that can go up and down (variable voltage) the 12v is not static.

 

[SnowFox]

Has the battery ever been replaced? If so I bet who ever replaced it did not reset the BMS Battery Monitor System which will cause issues with a new battery.

BMS in modern cars will typically recalibrate itself for the same TYPE of battery. Switching SLA to AGM or to Li+Ion may warrant differently.

 

[Farkel]

The BMS reset zeroes out the days-in-service parameter. Letting the car sit locked for 8 hours allows the system to determine the state-of-charge. These are two different things, both of which are used to calculate the charging strategy for the alternator.

 

[shadow1966]

What was he doing when he said that?

The alternator. Assuming you just stopped at the store should be a bit hot. Along with most things in the engine bay. (Obviously)

Output voltage? Like noted that can go up and down (variable voltage) the 12v is not static.

Oh sorry for the misunderstanding. He was running an Analog Test (If I remember correctly ) while the engine was running. I would assume it was probably voltage running high, but that was never explicitly said

 

[shadow1966]

I realized I completely forgot to mention the car only has around 20k miles on it, which is a part of the reason why I was surprised the alternator would be out so quickly.

It also doesn't appear like the battery has been changed before, so I'll take the car on a long drive and if that doesn't seem to improve anything I'll probably end up changing the battery first.

 

[ORRadtech]

I realized I completely forgot to mention the car only has around 20k miles on it, which is a part of the reason why I was surprised the alternator would be out so quickly.

It also doesn't appear like the battery has been changed before, so I'll take the car on a long drive and if that doesn't seem to improve anything I'll probably end up changing the battery first.

You should absolutely charge the battery before hand. As I said before, the alternator is not meant to recharge a dead battery.
I have several chargers from 1.5A maintenance chargers to a 225A starting charger. The one I use on a weak/low battery is an automatic 8A one that senses the battery charge and adjusts accordingly. I usually put it on overnight and only the worst need longer.

 

[KeyLime]

I'm not sure what problem you're chasing. The original problem was that the car was cranking for a while before starting. The battery tested okay, but it was low. Also the charging system was running hot (overcharging?).

How can a good battery be undercharged by an overcharging alternator isn't making sense. I get that an overcharging system can damage a battery, but then the damaged battery wouldn't test okay. If it's cranking, why doesn't it start right away? If the battery is bad how can it be cranking okay?

There's something missing here.

Be wary. There are so many OWT's about BMS and batteries it's becoming comical. Flat tires, streaking windshield wipers, thrown rod - change the battery, reset the BMS, and all will be good.

 

[SnowFox]

Oh sorry for the misunderstanding. He was running an Analog Test (If I remember correctly ) while the engine was running. I would assume it was probably voltage running high, but that was never explicitly said

Keep eye on it for peace of mind. But I wouldnt read to far into what he said unless your experienceing some new symptoms as time goes on.

 

[Boosted Pony]

If the battery has been replaced and the BMS was not reset the system thinks there is an old battery in the car so it will determine how many volts the system will need to maintain the old battery not the new battery in the car. As another post stated the BMS knows how many days the battery has been in the vehicle so if the battery has been in the vehicle for 4 years (1,460 days) it can over charge a new battery because it does not know the battery has been replaced. An older battery will need more charge to maintain it than a new battery will, that is why you must reset the BMS system so it knows there is a new battery.

This parking the vehicle for 8 hours with the doors locked does not reset the BMS system. The best way to reset the system is to use a scanner that has the ability to reset the BMS system, if you don't have that then look up the video that shows how to do a manual reset of the BMS system.

Until the BMS system has been reset for the new battery every diagnostic suggestion is just a guess that is likely leading down a path to no where.

Remember the key here is the car was bought used so we don't know if the battery is the original or if it was changed at some point, is the battery the motorcraft brand? If so was it ever changed and replaced with another motorcraft or is there an aftermarket brand battery in the car. There should be an inservice date on the battery to show when the battery was put into service.

It might be that the battery is just old and while it might still check good the charging system (BMS) is supplying more volts to keep the battery charged so the alternator could be showing higher voltage during a test due to the old battery.

I just replaced my battery in my 2021 Mustang it was 4 years old and I noticed every now and then it cranked just a little slower than normal. A batteries life is normally about 4 to 5 years, some will fail sooner some will last longer, my motorcraft battery checked good when I ran a test on it but the voltage was down a little like you have described on your battery. I replaced the battery with a Duralast Platinum EFB (Enhanced Flooded Battery) and reset the BMS and all is good again, the engines cranks normally again.

If the battery was replaced in the car in the post and the BMS was not reset the new battery while it still tests good is down on voltage and was likely damaged due to the BMS not knowing the battery had been replaced and was over charging it and now the battery will need to be replaced again and this time the BMS system needs to be properly reset.

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