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Discussion Starter · #1 · (Edited)
Can the solid alternator pulley in a 94 Taurus GL with a 3.8L engine, be replaced with an OAD (overrunning alternator decoupler) pulley, for smoother belt rotation? Are these appropriate pulleys for the 1994 3.8L and its alternator? According to several YouTube videos (see one below), a solid pulley on the alternator can cause vibration of the belt and the belt tensioner, but does this vibration happen only on engines designed for an OAD?

 

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I have never seen a belt fluctuate like that at all and even if I did I would look to the other parts first. Unless you have seen the problem and have replaced all the other parts I would look elsewhere.
 

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Discussion Starter · #3 ·
I have never seen a belt fluctuate like that at all and even if I did I would look to the other parts first. Unless you have seen the problem and have replaced all the other parts I would look elsewhere.
I should have been clearer: I wasn't seeing that kind of movement on my Taurus's belt (the video is of an engine that requires an OAD pulley), but I'm wondering if using an OAD pulley might still give some benefit on a 1994 3.8L engine, for instance possibly resulting in less unnecessary load by the alternator on the system.
 

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Waste of time and money, IMO. Alternator power output is regulated by the regulator. Engine HP drawn by the alt varies with the alts power output. Alt never draws more HP from the engine than it needs to run the electrical system.

Could always use the WOT AC cutout PCM output to set something up to disable the alternator from producing power (interrupt regulator key on power feed) at WOT. Might net you .5 to 1 extra WHP, which wouldnt be worth doing anyway.
 

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Discussion Starter · #6 · (Edited)
Waste of time and money, IMO. Alternator power output is regulated by the regulator. Engine HP drawn by the alt varies with the alts power output. Alt never draws more HP from the engine than it needs to run the electrical system.
I see what you're saying about the HP that the alternator draws from the engine--thanks for pointing that out. But I'm not so concerned about extra HP as I am about wear on things throughout the system. I got the impression by reading about OADs, that they might reduce excess mechanical load that the mass of the spinning alternator places on the system as the engine revs up and down, even in an engine that doesn't require an OAD. By decoupling the variably-spinning alternator during these speed transitions, it may smooth out the belt travel, which might reduce stress on the engine and the accessories it's running (AC, etc). I also wonder if an OAD might mess up something on an engine that doesn't require one. I guess the only way to find out would be to buy one and try it, and take my chances, but I found today that they cost about $60-$130 as opposed to about $10 for a solid alternator pulley, and right now my budget won't let me indulge my curiosity.

Here's a link in which there's some discussion of this, both for use in cars and motorcycles:

OAD - Overrunning Alternator Decoupler pulley - Goldwing Technical Forum - Forums - Steve Saunders Goldwing Forums
 

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Discussion Starter · #7 · (Edited)
You are asking for an underdrive pulley then.
My impression is that an underdrive pulley would only partly accomplish what an OAD pulley would, but an underdrive pulley might have more negative side effects than an OAD, and wouldn't reduce the excess mechanical load of the alternator as it's spun up and down by the engine, as well as an OAD would, because an underdrive pulley doesn't decouple the alternator.

Wikipedia has some info on underdrive pulleys describing their side effects:

Underdrive pulleys - Wikipedia, the free encyclopedia
 

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My '95 3.8 has 225,000 miles and I see no problems with the stock alternator pulley. The tensioner bearing sometimes goes out, but the alternator pulley has had no problems. (If it ain't broke, don't fix it! Also, don't try to convince yourself that it is broken if it isn't. Stay stock, stay happy, save the money for something else. With any car, there is always something else.)

I would invest in a good belt over worrying about whether the OEM pulley is good enough or not. I like the Goodyear Gatorback belts. The police-spec one is an inch or so shorter, which probably helps with something right?
 

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I see what you're saying about the HP that the alternator draws from the engine--thanks for pointing that out. But I'm not so concerned about extra HP as I am about wear on things throughout the system. I got the impression by reading about OADs, that they might reduce excess mechanical load that the mass of the spinning alternator places on the system as the engine revs up and down, even in an engine that doesn't require an OAD. By decoupling the variably-spinning alternator during these speed transitions, it may smooth out the belt travel, which might reduce stress on the engine and the accessories it's running (AC, etc). I also wonder if an OAD might mess up something on an engine that doesn't require one. I guess the only way to find out would be to buy one and try it, and take my chances, but I found today that they cost about $60-$130 as opposed to about $10 for a solid alternator pulley, and right now my budget won't let me indulge my curiosity.

Here's a link in which there's some discussion of this, both for use in cars and motorcycles:

OAD - Overrunning Alternator Decoupler pulley - Goldwing Technical Forum - Forums - Steve Saunders Goldwing Forums
This isn't a problem on any of the Taurus motors from what I have seen. I don't think you will be saving much.

My impression is that an underdrive pulley would only partly accomplish what an OAD pulley would, but an underdrive pulley might have more negative side effects than an OAD, and wouldn't reduce the excess mechanical load of the alternator as it's spun up and down by the engine, as well as an OAD would, because an underdrive pulley doesn't decouple the alternator.

Wikipedia has some info on underdrive pulleys describing their side effects:

Underdrive pulleys - Wikipedia, the free encyclopedia
An UDP will only have problems if not properly done. I have been running one with no issues as well sold quite a few for the SHO and Vulcan with no issues.

The UDP does reduce the load on the accessories freeing up power and not working the accessories as much.

It may be in Wikipedia but right now it looks to be the opinion of 1 person as I see nothing backing it up.
 

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I have used UDPs on a number of engines over the years, and never had a problem.
 

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From what it looks like. OAD's are only intended for use on diesel engines. Theoreticaly speaking the crank on a diesel has moments of increased speed, which would normally overrun the alternator which has a built up rotating inertia....

Which is why you see the belt flutter and movement.

Gasoline engines don't run like diesels and run "smoother" so the use of an OAD would be senseless.

The OAD is only for the belt, tensioner, and the alternator's benefit...I don't think there would be a power gain. I've only seen belt flutter like that on older diesels.... It's really surprising to see that on a Transit van.


I can however see the benefit if you decide to cam out your car.. where the sporadic belt rotation from the engine's heavy cam would result in a similar effect.
 

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Discussion Starter · #12 ·
From what it looks like. OAD's are only intended for use on diesel engines. Theoreticaly speaking the crank on a diesel has moments of increased speed, which would normally overrun the alternator which has a built up rotating inertia....

Gasoline engines don't run like diesels and run "smoother" so the use of an OAD would be senseless.
Thanks, that makes sense. Though I've been reading that many modern gas-powered engines are coming with OADs for their alternator pulley. Maybe something about the design of some newer gas engines makes them turn the crank somewhat like a diesel.

But since a 1994 3.8L isn't what we now call a modern engine, and I'm not planning on making any modifications to it, I agree that putting an OAD on it would probably get me little benefit, if any, so I'm saving the money for the actual repairs the car needs. If I can justify the expense at some point, maybe I'll try an OAD and see what happens.
 

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Discussion Starter · #13 ·
An UDP will only have problems if not properly done. I have been running one with no issues as well sold quite a few for the SHO and Vulcan with no issues.

The UDP does reduce the load on the accessories freeing up power and not working the accessories as much.
Thanks. Any advice on a proper UDP for the 3.8, and any other considerations if I decide to do that? For instance, could a UDP reduce the amount of work done by the pumps for the compressor, oil, and water, to the point of not delivering quite as much AC and engine cooling as I'd like? I like to keep both myself and my engine cool during the summer!
 

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Popularity of OAD Decouplers Grows With Current Models | Motor | Find Articles at BNET

I found this article on it..

Article said:
Overrunning alternator decouplers (also referred to as isolating decoupler pulleys, or IDPs) help enhance engine efficiency and reduce emissions and noise, vibration and harshness (NVH). OAD pulleys also enable the alternator to "coast" freely in cases of sudden belt deceleration.
I wasn't that far off with my hypothesis.. in fact it's what I originally meant. The "increased speed" occurs in short bursts resulting in periods of deceleration causing the alternator to slow down..

well their main reason for doing this is for NVH... I don't understand how it "reduces emissions" and "increases engine efficiency".

I can see it benefiting motors with long expanses of belts like on the Transit..
 

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Thanks. Any advice on a proper UDP for the 3.8, and any other considerations if I decide to do that? For instance, could a UDP reduce the amount of work done by the pumps for the compressor, oil, and water, to the point of not delivering quite as much AC and engine cooling as I'd like? I like to keep both myself and my engine cool during the summer!
I am not sure if one has been made for the 3.8 unless a TBird one will bolt up.

So far with any UDP I have seen has not under driven the accessories by that much.
 

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The t-bird and the mustang pulleys do not bith the Taurus. The Taurus pulleys sit closer to the block.
 

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Popularity of OAD Decouplers Grows With Current Models | Motor | Find Articles at BNET

I found this article on it..



I wasn't that far off with my hypothesis.. in fact it's what I originally meant. The "increased speed" occurs in short bursts resulting in periods of deceleration causing the alternator to slow down..

well their main reason for doing this is for NVH... I don't understand how it "reduces emissions" and "increases engine efficiency".

I can see it benefiting motors with long expanses of belts like on the Transit..
Interesting read. I get the NVH thing, but not the emissions / efficiency.

My take: Yet another part that can fail, throw a belt, or leave you stranded when the spring inside breaks and the pulley turns but not the alt. Also this thing must have roller bearing inside of it, so another possible failure point. Sounds like a waste. Added complexity for totally minimal gains to anything.
 

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Discussion Starter · #18 ·
My take: Yet another part that can fail, throw a belt, or leave you stranded when the spring inside breaks and the pulley turns but not the alt. Also this thing must have roller bearing inside of it, so another possible failure point. Sounds like a waste. Added complexity for totally minimal gains to anything.
I agree. I've been finding a number of user reports online describing how their OAD pulley failed. I'm sure a new one would work for at least a couple or a few years, but I wouldn't want it to fail at an inopportune time/in the middle of nowhere. I may try one in the future just to satisfy my curiosity, but if it doesn't seem to be doing much for me that a solid pulley doesn't do, then I'd probably just reinstall the solid pulley.
 

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Discussion Starter · #19 ·
I am not sure if one has been made for the 3.8 unless a TBird one will bolt up.

So far with any UDP I have seen has not under driven the accessories by that much.
Thanks. I've decided to hold off on trying to find and use a UDP until I've got my car running again for a while with a solid alternator pulley, so I can see how it behaves after the repairs I'm doing (new pulleys for belt tensioner and PS pump too, and a replacement compressor and its pulley/clutch).
 

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