# Alternator failure and mileage? **URL:** \ **Category:** Maintenance/Repairs\ **Created:** [May 11, 2025, 5:49pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220 "2025-05-11T17:49:08Z")\ **Posts on this page:** 20\ **Page:** 2
**Author:** ![JoeTro](https://avatars.discourse-cdn.com/v4/letter/j/13edae/32.png) [@JoeTro](https://community.cartalk.com/u/JoeTro)\ **Post date:** [May 12, 2025, 3:01pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/21 "2025-05-12T15:01:25Z")
Set to 20v scale. I should have worded it " set to be able to read above 12v". ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [May 12, 2025, 3:36pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/22 "2025-05-12T15:36:59Z")
> [@JoeTro](#): > > Set to 20v scale. I should have worded it " set to be able to read above 12v". Welcome to the forum Joe, if you decide to stick around and help out, you will find you have to cross your T’s and dot your i’s or you will get called out on it, for some reason it seems that you have to be an English major to be a member here… Trust me… 🤣 ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [May 12, 2025, 3:48pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/23 "2025-05-12T15:48:26Z")
Not an English major, but if your going to give advice at least make sure you’re technically correct. Imagine someone with little experience using a meter pulling their hair out looking for a 12 volt scale Tester ---
**Author:** ![jtsanders](https://avatars.discourse-cdn.com/v4/letter/j/c2a13f/32.png) [@jtsanders](https://community.cartalk.com/u/jtsanders)\ **Post date:** [May 12, 2025, 6:40pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/24 "2025-05-12T18:40:45Z")
> [@davesmopar](#): > > you will find you have to cross your T’s and dot your i’s or you will get called out I’m watching you, Dave. Slip up once and it’s knives out!!! 😜 ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 12, 2025, 7:54pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/25 "2025-05-12T19:54:14Z")
I am debating whether to take advantage of the 20% sale that ends today and get a reman alternator from the local store - I guess it might be on again for July 4th: - car has 145k. It appears that Alternator fails 100k to 150k as per internet - I tightened the belt that has been slipping since 2yrs ago on and off. Belt might be fairly used condition too - I can not recognize hairline cracks. - car is moving to East cost - conditions are likely severe in East cost. I do not want my family member to be stranded in the middle of the road. ---
**Author:** ![VOLVO-V70](https://avatars.discourse-cdn.com/v4/letter/v/8e8cbc/32.png) [@VOLVO-V70](https://community.cartalk.com/u/VOLVO-V70)\ **Post date:** [May 12, 2025, 7:57pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/26 "2025-05-12T19:57:54Z")
Why the reluctance to put a new belt on ? ---
**Author:** ![Tester](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/tester/32/15976_2.png) [@Tester](https://community.cartalk.com/u/Tester)\ **Post date:** [May 12, 2025, 8:03pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/27 "2025-05-12T20:03:06Z")
> [@sciconf](#): > > I can not recognize hairline cracks. You cannot tell if a belt is worn or not by visual inspection anymore. Belts today are made of EPDM rubber and not neoprene rubber. [![](https://global.discourse-cdn.com/cartalk/original/3X/5/a/5a84699f85c7109f7b4f8c829fc2cdf9c184f05e.jpeg "Belt wear gauge") ](https://www.youtube.com/watch?v=fz5EhxdLKsk) [![](https://global.discourse-cdn.com/cartalk/original/3X/9/3/934eb36a9ab04ef6be34c6541aa13ee6a74a5290.jpeg "How to Check Serpentine Belts for Wear") ](https://www.youtube.com/watch?v=wP9BtcBJOtw) Tester ---
**Author:** ![It\_s-Me](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/it_s-me/32/12660_2.png) [@It\_s-Me](https://community.cartalk.com/u/It_s-Me)\ **Post date:** [May 12, 2025, 8:13pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/28 "2025-05-12T20:13:25Z")
> [@sciconf](#): > > I tightened the belt that has been slipping since 2yrs ago on and off. If it’s been slipping for 2 years, it’s bad. ---
**Author:** ![old\_mopar\_guy](https://avatars.discourse-cdn.com/v4/letter/o/6bbea6/32.png) [@old\_mopar\_guy](https://community.cartalk.com/u/old_mopar_guy)\ **Post date:** [May 12, 2025, 10:14pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/29 "2025-05-12T22:14:42Z")
Ah, cmon Dave, we know you’re not en English major and we don’t pick on you. ---
**Author:** ![JoeTro](https://avatars.discourse-cdn.com/v4/letter/j/13edae/32.png) [@JoeTro](https://community.cartalk.com/u/JoeTro)\ **Post date:** [May 12, 2025, 10:50pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/30 "2025-05-12T22:50:27Z")
It’s pretty obvious what was meant. I mean, c’mon on. Give it a rest and let’s all enjoy ourselves here. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 13, 2025, 1:24am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/32 "2025-05-13T01:24:07Z")
> [@sciconf](#): > > So what did really go wrong yesterday? Alternator has intermittent issue? You stated that the alternator was tested twice, but what about the battery? The battery was tested, what were the results? What was the battery state of charge after the jump start? How many minutes was the engine run after the jump start and before the battery test? How long were the doors left open at the car wash? Were the headlights left on? Has this car been driven daily? > [@sciconf](#): > > I am debating whether to take advantage of the 20% sale that ends today and get a reman alternator from the local store Keep the original alternator, you may need to use it again before long. Those cheap aftermarket parts with the “Lifetime Warranty” are unreliable, people that use them often remark “Bad-out-of-the-box”. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 13, 2025, 10:15pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/33 "2025-05-13T22:15:46Z")
The car drove 12k in the past 12months. The belt slipping is intermittent. Shop underplayed it and now I just tightened it. Battery passed without an issue - so less emphasis on it. It has Apr 2021 on it. 4 yrs of age! Head light was never left on. Door was never left opened unnecessarily. _ **I still do not know why the car was able to start and I drive to the car wash place for 1 mile.** _ **After the car wash, battery lost charge that it could not be started but power window works!** **Its once of the kind event so far.** I learned that the diode (?) prevent loosing charge of the battery - it might be going bad (or shortened during the car wash). Alternator was going bad? I do not know of any other explanation. I have not bought an alternator yet. Another shop owner said that has a 30yr old Toyo with 180k miles and still on its original Alternator. Online shows on average they fail between 100k to 150k. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 13, 2025, 10:46pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/34 "2025-05-13T22:46:43Z")
> [@sciconf](#): > > After the car wash, battery lost charge that it could not be started but power window works! How can you be certain the battery was discharged? Do you carry a volt meter in the car? The contacts in the starter solenoid could be failing. Perhaps you forgot to shift into park when you stopped the car. There are many reasons for an engine to fail to start. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 13, 2025, 10:57pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/35 "2025-05-13T22:57:41Z")
> [@Nevada\_545](#): > > How can you be certain the battery was discharged? Do you carry a volt meter in the car? The contacts in the starter solenoid could be failing. Perhaps you forgot to shift into park when you stopped the car. There are many reasons for an engine to fail to start. Because right after this failure the voltage was 13.62v when the engine was running - when I rev, it went to 13.7v. Nxt morning it was 14.x v irrespective of rpm. I was keep testing. Car wash was just a mile from home. ---
**Author:** ![Nevada\_545](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/nevada_545/32/41232_2.png) [@Nevada\_545](https://community.cartalk.com/u/Nevada_545)\ **Post date:** [May 13, 2025, 11:32pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/36 "2025-05-13T23:32:38Z")
> [@sciconf](#): > > right after this failure the voltage was 13.62v when the engine was running That was the charging system voltage, this shows the alternator was working. What was the battery voltage when it was “dead”? Generally, when you start a car with a discharged battery, it takes a while before peak voltage or target voltage is reached, you won’t see 13.6 volts at idle. ---
**Author:** ![davesmopar](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/davesmopar/32/41750_2.png) [@davesmopar](https://community.cartalk.com/u/davesmopar)\ **Post date:** [May 14, 2025, 1:30am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/37 "2025-05-14T01:30:53Z")
Turn your head lights (key off/out) on for 10-15 minutes, then start car, if battery dead then replace it, you should have at least a 20-30 minute reserve of battery life in it… Basically it is a cheap load test on the battery… ---
**Author:** ![Jerome-Silverman](https://avatars.discourse-cdn.com/v4/letter/j/71e660/32.png) [@Jerome-Silverman](https://community.cartalk.com/u/Jerome-Silverman)\ **Post date:** [May 15, 2025, 7:51pm UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/38 "2025-05-15T19:51:15Z")
There are 6 power diodes in the automotive alternator. A diode can fail shorted, open, or intermittently. One end of each diode has a soldered or welded connection that can also be problematic. A test instrument can provide a misleading indication, depending on it’s design. On the cars that I have had that used a serpentine belt , it would have been practically impossible for the belt to slip unless it was ready to break. Some alternators have an overrunning clutch on the pulley that can make a noise like a slipping belt or worse. There are lots of other things that could have caused your problem. Did you check for any diagnostic codes? ---
**Author:** ![bing](https://sea1.discourse-cdn.com/cartalk/user_avatar/community.cartalk.com/bing/32/4619_2.png) [@bing](https://community.cartalk.com/u/bing)\ **Post date:** [May 16, 2025, 12:31am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/39 "2025-05-16T00:31:57Z")
I used to overhaul my alternators at about 70,000. Brushes, bearings if needed, regulator, and the diode trio. In the gms it was three diodes. I’d pay about $25 for the parts and about an hour on the bench. Then they started crimping and riviting everything so I gave up. ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 19, 2025, 4:52am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/40 "2025-05-19T04:52:51Z")
I was quoted a overhaul price that is almost the price of OReilly auto which gives lifetime warranty. Rock Auto had good price but limited warranty. Anyone know who pays for shipping the core? ---
**Author:** ![sciconf](https://avatars.discourse-cdn.com/v4/letter/s/919ad9/32.png) [@sciconf](https://community.cartalk.com/u/sciconf)\ **Post date:** [May 19, 2025, 4:57am UTC](https://community.cartalk.com/t/alternator-failure-and-mileage/200220/41 "2025-05-19T04:57:43Z")
Data seems to point that somehow battery lost the charge and lost voltage. It failed right after the car wash - coincident or otherwise I do not know. Since then no issues - I also tightened the belt. Batt voltage was 13.6v with engine running right after the failure. When revved up voltage went to 13.7v. But the next day Batt voltage with engine running was over 14v irrespective of rpm! This proves Batt had lower voltage which caused the failure. Why batt lost charge, we do not know. [Previous page](https://community.cartalk.com/t/alternator-failure-and-mileage/200220.md?page=1) [Next page](https://community.cartalk.com/t/alternator-failure-and-mileage/200220.md?page=3)