z driver 88t

This is a tangetially related post to the one asking about duct replacement. I was replacing my alternator a few weeks ago, and reinstalled the duct because everyone says to.

This may be a dumb question and I am probably overlooking something obvious, but...

the alternator seems to incorporate a fan with the pulley on the front side that forces air front to back. There is no extra fan in the duct that sucks air through or contributes to pulling air through the alternator. So if anything it seems like the best airflow through the alternator would be one with no duct (i.e. flow restriction - analogous to an open header vs. a very long exhaust pipe) or at the very least I can't envision how the duct contributes to cooling.

Maybe (this is a stretch) since the duct exits in the wheel well (cooler area) and hot air rises there is a "passive fan" created in the duct that aids in moving the air just based on the air temperature differential within the duct (sort of like a chimney)???

I CAN see value in the duct protecting the internals by helping to prevent water and debris from getting into the back of the alternator and I'm thinking maybe that is really it's purpose.

ROG100

Chris I always thought the fan sucked air through the alternator back to front.
Therefore also sucking ambient air passed the external temperature sensor.

z driver 88t

Oh...OK. That would explain a lot. Thanks Roger. I had assumed it was the pushing air through.

WallyP

The fan is a centrifugal type. Spinning throws the air outwards from the fins, creating a low pressure area in the center, pulling air from the back to the front.

With no duct, you are pulling air that was heated by passing thru the radiator, then heated more by the exhaust manifold. Add a little oil vapor from the power steering leaks, and the alternator has a hard life.

In addition, as Roger says, the air flow ensures that the HVAC external air temp sensor gets a true ambient reading.

The duct is a good thing...

kmascotto

I am in the process of...several things...one being that Air duct. Here are several photos of the problem

mark kibort

its purpose is to suck rocks and pebbles into the alternator, so they can bounce around in the alternator and break armature wires, so you need a new alternator. ask me how i know...

dont forget to put a filter over that inlet to the alternator.... i use a lady's nylon sock

Dave928S

You do have the alternator hose running from the alternator across and up behind the front LH splashshield Mark ??

It sounds like you are advocating putting a sock over the the inlet that you never had a hose on ?? ... if that is the case (no duct) then it wouldn't be surprising to me if you'd picked up debris .. and water ... and very hot air .. all of which will stuff up an alternator.

To the OP ... As Wally noted, the duct is a good thing. Look at the position, in close proximity to the road surface, and you can see why that duct is vital ... if you value your alternator.

worf928

The only alternators I have had to replace were mounted without the duct. (Not saying that they won't fail with the duct; but my data shows that not having the duct is a bad thing.)