Hi everyone,

I've noticed a sound that's been bugging me lately and honestly I'm not even sure it's abnormal. It's just slightly louder than the normal engine din, and the best way I can describe it is a constant mechanical hum or whir. It's not periodic, and honestly it's kind of "mid" pitched, neither too high or low (goldilocks sound!).

It's constant regardless of whether or not I have the clutch in, but does seem to vary with engine RPMs. It's hard to tell for sure because the engine is louder than the sound I'm hearing more or less right above idle. It'll also get slightly lower pitched when turning the steering wheel. My initial thought was PS pump, but I see a corresponding slight drop in voltage and RPM on the dash so it's probably just related to the extra load on the engine? A/C has a similar effect; initial drop in pitch that then recovers.

Right now I'm leaning toward something that's belt-driven, either alternator, water pump, or PS, but hopefully just an idler pulley.
Does the alternator have a serviceable clutch pulley? If so I guess it could be something like that as well.

I guess what I'm asking is if anyone's experienced anything similar and if so what did it end up being? I can always turn up the radio, but I'd rather diagnose/fix the issue if possible. Otherwise does anyone have any tips to help me diagnose?

 

Reads like a noisy accessory drive or possibly (and more likely) a noisy idler (or tensioner) roller bearing.

With the engine idling and the noise present you need to get out of the car and open the engine compartment lid. Be careful! If the engine is hot enough the fan in the lid can come up so do not put your fingers in the area of the fan blade.

Do not stick your hands in around the engine either. Just carefully listen and move about to see if you can pinpoint the source of the noise.

You probably won't be able to precisely determine the source of the noise.

When my 03 Turbo developed a "dry bearing" sound with the car on a lift at a shop in Tehachapi CA the owner and I narrowed it down to idler roller bearing up high. At my local dealer a day or so later the noise proved to be from an idler roller bearing located next to the power steering pump.

If it is a noisy accessory drive the most common source is the water pump.

One sign that an accessory drive is responsible for the noise is the belt will develop a sharp edge this from rubbing on the side of the pulley of the accessory drive with play.

You do need to diagnose this noise and have it fixed. It will only get worse and if it is a water pump you do not want the pump to suffer a catastrophic failure. 'course the same goes for even a simple idler roller bearing.

 

Thanks. Sounds like I'm on the right track then. From what I've read if the water pump itself goes out, It should start leaking through a weep hole first right? That way you can spot it and fix it before it seizes up and nukes your engine? I haven't lost any coolant that hasn't evaporated through the cap (still have the old cap, need to upgrade that too) so I think I'm okay there for now, but I'll definitely try and give the pump pulley a turn and see how it sounds.

Is there any harm in starting the car cold w/o the belt? if the thermostat is cold there shouldn't be any danger of not having the water circulate, and if I cut accessory use to a minimum and don't turn the wheel or anything I would think I'd be okay. That way I can at least narrow it down to the belt or 1000 or so pulleys that it turns.

How would you describe a "dry bearing" sound? I guess I can do some youtube research for it. All of these sounds are new to me since I'm used to hearing most engine noises coming from in front of me (save for when my wife owned her MR2 spyder). Funny how much of a difference that can make.

 

A stethoscope or long handled screw driver held against a solid mounting point etc can be very helpful in pinning down problem. You can pull belt and spin pulleys while feeling for rough spots and listening for abnormal noise.

 

You do not want to let a suspected bad water pump go.

The water pump on my 03 Turbo (with 110K miles) had to be replaced. No leak, at least no visible leak. But the engine got a bit warm based on the temp gage needle and I smelled a whiff of antifreeze so I took the car in. The tech checked the car over and found the driver's side radiator fan not working and he suspected the t-stat was bad. The car had a failed radiator fan once before and never got any warmer at all.

So, I booked the car in for a new fan, t-stat. On the rack the tech managed to spot leak sign at the water pump. The antifreeze had been leaking out -- but not bad enough to lower the coolant level to the point the warning light was triggered on -- and left a deposit of antifreeze residue. Hard to see -- a good view of the water pump is blocked by a metal shield -- but it was there. (Out of the car the residue is easy to see. Quite a lot of build up actually.) There was never any fluid on the ground nor any sign of any fluid on any part of the car. Apparently the antifreeze would leak out only when the engine was real hot and evaporate and as a result a sizable amount of antifreeze residue accumulated.

So, the tech replaced the water pump and t-stat and the non-runnng radiator fan motor.

Regardless of what else you do, you need to replace the old cap too with a newer one.

You can start and run a cold engine with no belt. I've run my Boxster a minute or so from cold to confirm a noise that proved to be a bad water pump was not present with the belt removed.

FWIW, I've driven the Boxster about a block with no coolant in it from a cold start with no harm.

You want to be sure the noise is present at a cold start or shortly thereafter. You can't or shouldn't run the engine too long, say run it long enough to get hot to see if the noise appears.

Be sure you note the belt routing so you can install it again correctly. And if you reuse the old belt be sure you have the belt running the same way as before.

I do not know how to describe a dry bearing sound but that is the description that came to me when I heard the noise. Others that listened agreed with the description or at least offered nothing better.

All I know is the noise didn't belong, it was a new noise, and thus cause for concern.

There is not that much difference between the Turbo and its engine at the rear vs. a car with its engine at the front. The accessory drive of both engines while they face opposite directions are at the end of the car. The front engine car likely has a radiator between the accessory drive and you at the front of the car while the Turbo doesn't but the Turbo has more plastic/sheet metal between the accessory drive and you standing/listening outside of the car.

 

Definitely not. I'm hoping to be able to diagnose where the noise is coming from this weekend, and I plan on checking out all the belt driven components while I'm back there. I'll update the thread if/when I have my findings.

One of the big differences is the location of the exhaust vs the engine. It makes it harder (for me at least) to differentiate engine noises from post-engine exhaust path kind of noises. A loose heat shield on the exhaust might be easy to identify as such in a front engined car vs a rear, for example. Also it's just a weird beast in general.

And not to be pedantic, but the serpentine belt on my transversely mounted V6 minivan is on the side of the car, and not at the end

... I guess that was pretty pedantic after all. Oh well. Thanks for all the help so far, here's hoping for a bad idler or tensioner pulley!

 

Exact same symptoms I had with a bad tensioner pulley.

 

anyone have the part #s for the tensioner and idler pulleys? Is the tensioner pulley just another idler that's bolted to the tensioning device/spring? They look the same from what I've been able to see but I wouldn't be surprised if Porsche spec'd them different because Porsche. I'm probably gonna order a new belt and pulley set since I need to get the belt off to check anyway and the car's at 54k miles.

 

For future reference, the tensioner pulley is different:

http://www.autoatlanta.com/porsche-p...=99611501672#a

P/N 99611501574 which has been superseded by P/N 99611501575

Naturally it's like 5x the cost of a normal replacement idler pulley. Still hoping it's one of the cheap ones.

 

Update (6mo old makes for a protracted investigation):

Removed the belt and started the car without any of the accessories. Didn't hear the noise but I didn't drive the car for any extended period. Played with all of the pullies, and there wasn't any noise that I'd characterize as abnormal. A tiny bit of bearing noise from the idlers, but I'd be hard pressed to tell if from new; I've heard much worse before.
The loudest pulley was the AC clutch, and even that wasn't anything I'd be concerned about (side note: does anyone know if you can buy the pulley or bearing for the AC compressor separately? A whole unit is a couple hundred bucks, but I don't have the tools to dis/recharge the system and replace the whole thing so I'd rather not). Also, if it was the AC clutch bearing causing the noise I would think I could just turn on the air conditioning inside the car and the noise would go away since the outer pulley wouldn't be rotating relative to the inner one(?).
I put the new belt on as part of an early 60k service, and started the car up. At first I didn't hear the noise at all, and then only when I'd turn the wheel slightly, just long enough for the power assist to do its thing. By the time I was done with my test drive the noise was back to what it was before I put on the new belt. I'm guessing it's something related to the pump, but I'm not 100% sure. Fluid levels looked good last I checked, but I'll recheck them next time I drive the car. It was overfilled when I bought the car, but I think some of that has to do with the previous owner compensating for the shot slave cylinder. Steering is smooth and definitely assisted, so the rack is fine at least. Clutch is smooth and plenty boosted too. I guess I could just have a noisy pump. Next steps are to double check the fluid and get a mechanic's stethoscope to try and pin down the noise.

 

Check the tensioner pulley slightly below and to the left of the power steering unit, that's the one that went bad on my car. It's difficult to isolate the sound from the power steering pump from the rear of the car with the engine cover up, my tech misdiagnosed it at first. It may not make noise with the belt off, but does when it is loaded. Definitely changes sound with the RPM's.

 

^ yeah, that's the one that's hard to spin/check since it's sandwiched between the AC and PS pullies, and the engine carrier is in the way. I'll order the two idlers anyway, since it's cheap and might as well replace them at the same time as the belt. I'll report back with my findings.

 

Update again!

I was finally able to remove all of the idler/tensioner pullies and really inspect them. Unfortunately for me, all three sounded just fine with no worn or dry bearings.

I ended up taking the car to local independent to help me diagnose the noise (Fix N Go in Plano, which despite the name actually has a good reputation servicing P-cars). They took one listen and said it was the power steering pump. From what the tech could hear, it's nothing I need to worry about any time soon, but the noise isn't going to go away on its own so I'll probably end up replacing the pump when I can get around to it.

Also, just in case anyone is curious in the future; Dayco part #89173 is NOT a valid replacement part for our idler/tensioner pullies. The Dayco wheel is about 10mm narrower (70.3 mm vs ~80 for the Mubea OEM part) in diameter, but would otherwise fit. Lots of parts sites list them as a direct fit replacement. nope nope nope. I'm guessing it'll fit some variety of porsche engine, but definitely not ours. TheMoreYouKnow.jpg