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"AestheticsInMotion" (aestheticsinmotion) 03/13/2018 at 20:59 • Filed to: None

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I have new info on my belt/alternator/whatever issue so maybe someone will have an idea of what’s going on.

Voltage is dropping when I’m driving slow or stopped. Drops from 14-14.2 to 11.9-12.6 and then starts squealing like crazy. If I shift into neutral volts will slowly rise back up to 14 and then the squealing will stop, but if I engage the clutch, press the gas or brake pedal AT ALL before it gets back to 14 volts, it will instantly drop back down to 12ish volts and keep squealing.

So... Whats causing the voltage drop? I thought I had a belt issue, but now it’s looking like an electrical problem. Battery is brand new, alternator will be tested this weekend. Halp

Oh a d this has been happening since long before I added a stereo and other accessories so I can’t imagine power draw would play a factor

gmporschenut also a fan of hondas > AestheticsInMotion 03/13/2018 at 21:10

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does the belt show any wear?

Do the pulleys have any slop?

ITA97, now with more Jag @ opposite-lock.com > AestheticsInMotion 03/13/2018 at 21:12

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The belt is likely slipping and the alternator output is dropping to little/not enough, and especially so at idle. There a two accessory belts on your miata. One drives the water pump and alternator, and the other drives the A/C (or delete pulley in place of the compressor if the car wasn’t equipped with A/C) and the power steering pump. Both have threaded adjusters. Losen the lock bolt on the adjuster, then losen the pivot bolt on the alternator (or P/S pump on the other belt), tighten up the adjuster to increase tension on the belt, tighten the lock bolt and pivot bolt on the alternator. The water pump/alternator belt tends to require more tension than you guess to keep them from squealing. If you’ve got more than a quarter inch of deflection in that belt, it is too loose.

AestheticsInMotion > gmporschenut also a fan of hondas 03/13/2018 at 21:17

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They look fairly old, but so does everything that I haven’t replaced yet. I can read all the writing on the belts, not sure if that’s a good indicator of age...

I’m checking for slop as soon as I get home.

AestheticsInMotion > ITA97, now with more Jag @ opposite-lock.com 03/13/2018 at 21:20

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Thank you so much. This sounds like a likely culprit. One question. If it is a loose belt—specifically the water pump/alternator belt—what problems would a slipping belt cause in relation to the water pump?

MM54 > AestheticsInMotion 03/13/2018 at 21:31

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Sounds like the belt is slipping on the alternator. I think I remember seeing V-belts in your other picture? If so, a quick shot of belt dressing will be a good help in diagnosis - if it makes it stop, I’d replace and re-tension the belt.

AestheticsInMotion > MM54 03/13/2018 at 21:53

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I’ll grab a bottle, see what happens. What are V-belts? Are these?

MM54 > AestheticsInMotion 03/13/2018 at 21:55

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Those aren’t v-belts, so don’t bother with the dressing. I’ve never tempted it, but it does say right on the can not to use it on serpentine belts such as those.

An alternative is to spray or pour some water on the belt and see if it makes it worse

MM54 > AestheticsInMotion 03/13/2018 at 21:56

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Here’s a v-belt, it’s v-shaped as opposed to flat (these are both v-belts, just two different types)

ITA97, now with more Jag @ opposite-lock.com > AestheticsInMotion 03/13/2018 at 22:23

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It could also drop the output of the water pump, but it may or may not drop enough to cause a temperature rise. The water pump pulley is fairly big compared to alternator, so the increased surface area could be enough for the water pump to work fine but the alternator pulley slips.

ITA97, now with more Jag @ opposite-lock.com > AestheticsInMotion 03/13/2018 at 22:25

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Look at the underside of the belt. If it is cracked, looks glazed or is missing chunks from the ribs, grab a new belt to put on (and grab a new A/C, P/S belt, too, since you have to remove it to replace the alt/water pump belt.