todor

Hi all, I just started hearing some weird noise from the passenger-side intake inlet on my 2000 Boxster S. Previously I've heard regular fan noise from there when the engine starts getting hot... but now it sounds like the fan blades are hitting something... but only at low RPM. The sound varies with RPMs and disappears above around 2k (actually once I go higher than 2k and then come back down to idle, the noise is gone for some time, but then comes back again randomly).

I searched but didn't find any accounts of a similar problem.

Is there really a fan in there, and is it common for it to break? Is it easy to replace?

Thanks in advance.

Macster

in the passenger vent opening. I've never heard or read about one going bad but there's always a first time.

Expose engine compartment from the top as you were going to service engine, then with engine *dead* cold or better yet battery disconnected -- pay attention to the proper method for doing this disconnect and note radio code before disconnecting -- examine the fan and fan shroud and blades for anything from a piece of paper, leaf, or perhaps some electrical tape or a piece of wiring harness --- anything actually -- the fan blades could be hitting.

The item may not be in the fan proper but close by and loose enough to be pulled in when the fan's running and of course everything's hot and more pliable.

Check fan blades for any signs of contact with fan shroud (loose fan motor bearings) or a loose or damage shroud and check fan for excessive axial or radial shaft play.

If you find something the blades are hitting well that's your noise source. If you find evidence blades making contact with shroud or shroud making contact with blades then likely you're looking at a new fan.

One last thing: check leading edges of the fan blades. In the past I've found PC power supply fans get very loud as dust/lint build up on the leading edges of the fan blades. If there is any buildup of dust/dirt on the engine compartment fan blades and no signs of an contact by the blades with anything and no signs of any debris in the blades -- it might be worth the effort to clean the blades with just a clean lint free rag dipped in hot water and wrung free of any excess water -- you do not want water running down blade into motor internals -- and see if clean blades make fan quieter.

The build up can be uneven and the resulting vibration can mimic the noise you hear.

Sincerely,

Macster.

todor

Thanks for the detailed info Macster. I'm going to open it up today and see what's going on in there.

Actually, I have another suspicion: it may not be a fan at all, it may be the accessory belt because a few times when I heard that noise, the battery charge light and a few other lights blinked on and off a few times... so my theory is that maybe a bearing on a pulley is going bad and/or the belt is slipping... or is torn and hitting something... It's possible that the reason I'm hearing it through the passenger-side intake is that that's the closest location that's open to the outside... we'll find out soon.

99firehawk

Sound like a water pump, make sure you check it when you have it open up. Stick a small screw driver between the pulley and the case and gentaly pry it away from the case if you have alot of movement its toast

todor

Turns out the noise is coming from the alternator. I think it's the pulley but I guess there's no way to distinguish between the alternator itself and its pulley... or is there?

I used an automotive stethoscope to hear exactly where the noise is coming from. I didn't check the water pump, but the noise was definitely more pronounced at the alternator than at the idler pulleys or power steering pump... and the sound is coming somewhere from the top passenger-side of the engine, so out of those, it's definitely the alternator.

I guess I'll just buy a new pulley and hope that that solves the problem. Do you guys have any other suggestions of how to verify that it's indeed the pulley? I tried spinning it by hand, but I don't know how a freewheeling pulley is supposed to feel... the alternator rotor itself seems to spin freely, without any grinding or anything.

99firehawk

Its not the alternator pulley. PLease check your water pump. Is the noise present with the belt removed?

Macster

cover the one accessible inside cabin to expose front of engine and all accessory drives.

Open top and remove engine covers to expose top of engine.

Note belt orientation. When you put belt back on -- if you reuse belt -- you should put it on so it runs same direction as it was.

Note belt routing. Draw diagram. Check it twice for accuracy.

Remove belt.

Start engine. If noise not present noise likely coming from accessory drive.

Do not run engine too long. Should take you just a moment or two to note noise's presence or absece.

Check belt for signs of aging or pending failure. If you find any replace belt.

But before you do... Check each accesory drive pulley for signs of belt rubbing on either inside or outside pulley side. Belt should track in middle of each pulley and belt should not make contact with either pulley side.

The belt's edge can have a sharpness to it as well. Compare both edges. If you find a sharp edge then that's a sign some accessory drive going bad.

The pulley that you find with evidence of rubbing by the belt will be suspect #1.

In my car's case it was the water pump. A check of the water pump found a tiny bit of play in the shaft. By itself the small amount of play may not have seemed signficant but with clear evidence the belt had been contacting the inside pulley wall good enough for me to have water pump replaced.

Since the belt does not drive any pulley by friction on the pulley's sides unlike a V-belt which does, I find it hard to believe a pulley could be worn out unless due to some bearing play so much so the belt has been so off track it has managed to wear out pulley by contacting a side of the pulley.

In this case while pulley bad the underlying cause if the bearings of the accessory drive the pulley attached to are bad and this needs to be fixed. A replacement of the drive, say alternator, is called for. Unless you have access to a shop that can rebuild the alternator by replacing its bearings, renewing its pulley and refurbishing whatever else needs it inside the alternator.

Also check all idler rollers for excessive play -- compare each's play to that of the others. Unlikely all bad so the one with excessive free play -- if there is one -- is the bad one. Check tensioner roller too.

If you want while you are there you can replace all idler rollers and tensioner.

I've got new ones but have never had to replace them. Just had to replace the water pump.

Be sure when you put belt back on it is routed correctly and belt resides fully inside each pulley. Mind you don't get a twist in belt.

Sometimes this belt installation operation takes 3 hands but take your time and double and triple check. If belt not routed properly it can jump off or break or shred itself in short order.

Sincerely,

Macster.

THXBABE

My alternator just bit the dust on Friday. I noticed no clicking or undue noise from the engine before it went. The idle was a bit rougher than normal but that was it. Right before it completely failed, the battery light came on, then the ABS, brake fluid and air bag lights (one at a time).

Check the pulleys and the water pump.