Boxster engine running rattle (not startup)

[Horrible Head]

G’Day Boxster Brainstrust,

Long time lurker, first time poster so be gentle with me.. I say that, but I posted this yesterday however it seems I have fat fingers as it didn't appear. Apologies if it now turns up twice..

Alrighty, I have owned a ’97 Boxster for some time now, and shes generally been very good to me.. I’ve had the odd common issue such as the AOS and MAF but I’m currently trying to locate a ‘rattle’ in the engine bay that started just a couple of days ago.

I’ve posted a short video on YouTube hoping that someone might be able to assist.

https://youtu.be/5ZKDG1LkQJw

It sounds like one of the pulleys is striking on something, but it’s quite irregular as I’m hoping you can tell in the video.

I’ve slipped the serpentine belt off and the noise disappears with the engine purring like a kitten, so it’s not internal to the engine (Praise be!!).

The idler bearings were replaced not too long ago, certainly within 2000k’s, and they seem to rotate nicely and the bearings feel smooth. I’ve poked about using the old screwdriver to the ear method, and the lower idler did sound a bit noisier than the others, but I pulled it and again found it rotates nicely and feels smooth. I’m thinking that the lower idler is simply closer to the real source.

The AC pulley has a fraction of ‘wobble’ in it, which seems fine to me and the noise doesn’t change when the AC is engaged or disengaged.

The water pump pulley has a little more ‘play’ in it than the AC pulley, maybe up to .5mm which I guess indicates a little pump/bearing wear which probably needs to addressed in the next 10K or so but I don’t know if it would be responsible for the ‘irregular’ knock.. I’d expect it to be a little more rhythmic..

The Power Steering reservoir fluid level is spot on

If anyone has any suggestions for where to go from here, I’d appreciate hearing from you..

I’ve already tried drinking heavily, seems to only make the noise a little louder the following morning..

Cheers,

[NSW911]

I experienced a similar problem with my 2000 2.7 litre manual Boxster.

A rumbling noise would make itself heard at idle speed which at no time appeared at engine speeds above idle. I tried everything including the use of a plastic tube used as a stethoscope and eventually tracked it down to the freewheel lock on the alternator pulley. The freewheel lock mechanism had seized but not completely, allowing movement of the pulley back and forth at random, resulting in a low frequency and persistent rumble.

I was at a loss as to why this problem did not occur at higher RPM's but the fact remained that replacement of the pulley solved my problem.

Good luck with yours!

[Horrible Head]

Cheers for responding NSW911,

I've got no further with this, unfortunately.. Are you saying the ALT pulley was moving and causing the striking noise or the belt was tightening on the freewheel lock mech causing the belt tensioner (and pulley) to shift and chatter..

I only noticed this noise last week while pulling into my driveway/garage.. I'll have to have a listen while putting some revs on to see if it changes. I thinking that it doesn't make a difference, but I don't remember if I specifically gave it some revs..

Cheers,

[Horrible Head]

Alrighty Boxster Brains trust,

I've been away for a little over a month so didn't get to look further into this any earlier..

However, this morning I rigged up a temporary belt (read 'Wifes Panty Hose' repurposed) and managed to run all the pumps/pulleys individually with no 'rattle' to report.. which is a little disappointing.

I have noticed that there are some 'burrs/dings' on the crankshaft pulley though which I'm at a loss to explain, no corresponding area of nice shiny metal nearby that would indicate intermittent striking..

The Crankshaft pulley has zero movement in it, and it certainly doesn't look like (to me anyway) that there is any way the pulley could strike anything with engine vibration/movement.

Is it even possible for the crankshaft pulley to move independently and strike something in the immediate area?

Cheers in advance,

HH

[BYprodriver]

Might as well install a new Pierburg Water Pump, it may be the source of the noise & if it fails suddenly You may have to go "walk-about" &/or damage the engine.

[Horrible Head]

Resolved..

Water pump, despite the minimal play, was the source of the random noise.

The local 'Euro' independent recommended Valvoline 'ZEREX G-05', he uses it in his Porsche.. a less expensive alternative to the Porshe branded coolant.

Thanks to those that took the time to look, more so those that responded.

Cheers guys.

[BYprodriver]

Hmm