S80 mysterious whirring noise solved Topic is solved

Crito · Post by **Crito** » 15 Jun 2009, 06:56

I thought this whirring noise I had was some sort of harmonic that inline sixes produce, since others have mentioned it in the forums too. But then I noticed that people where saying it happened at different RPMs than mine, and you'd think a natural harmonic would be produced at the same oscillation/frequency. So I started poking around and discovered that there's a pipe that goes from a heat shield over the exhaust manifold (near where O2 sensors go) that runs into the air box -- and now I also know why my Volvo warms up so fast in the winter. Well, in one place it was touching the block. So I tied it down with steel wire to the lower radiator hose, being careful to wrap wire around metal part and not rubber. Took it for a test drive, whirring noise is finally gone!

I can't believe the problem was so stupid and the fix so simple. I'm attaching pics for reference.

Crito · Post by **Crito** » 15 Jun 2009, 11:04

Well, got 90% of the whirring anyways. Still a little ~1850-1900 RPM, but was like from 1800-2500 RPMs before, so I'm pretty sure that corrugated aluminum tube is the source. I'm gonna try a couple hose clamps tomorrow to dampen the vibrations some more and hopefully that'll make the fix 100% effective.

And if that doesn't work I might just remove the tube entirely. So my car warms up a little slow in the winter... I don't care, that noise was really bothering me -- sounds serious (like bearings or gears or something like that) even though it really isn't.

Crito · Post by **Crito** » 16 Jun 2009, 11:04

I don't know what the official name for this part is but I'm calling it the "Volvo guitar string". As you can see from pic the block was contacting almost dead center, where the natural harmonic is. The corrugation makes it vibrate like a guitar string. The tube and air box together act like a megaphone, amplifying the sound.

Anywho, I decided I didn't need it in there. It's not sucking exhaust gases (in the non-turbo 2.9L version anyways) just hot air from around exhaust manifold, so I don't think there's any danger. I'll keep sniffing around just to be sure.

Crito · Post by **Crito** » 17 Jun 2009, 06:07

Well, I still have the 1850-1900 whir but it's so slight I can barely hear it now. In fact, if rest of car wasn't so quiet I probably wouldn't hear it all all. So I'm keep the "Volvo engine noise amplifier" (my new name for it) out of the car permanently.

One last pic that's a little troubling. Seems that tube had been rubbing against the lower radiator hose and ate a bald spot in it. I estimate about 25% of the hose material is missing in one section. The tube also seems to have shifted positions, so I imagine if it had stayed in the same place it may very well have eaten through 50% or more of the hose and caused it to fail.

Post by **vegasjetskier** » 17 Jun 2009, 14:17

Crito wrote:Well, I still have the 1850-1900 whir but it's so slight I can barely hear it now. In fact, if rest of car wasn't so quiet I probably wouldn't hear it all all. So I'm keep the "Volvo engine noise amplifier" (my new name for it) out of the car permanently.

I'd just keep it handy. You might want to reinstall it should you move to Alaska.

Crito · Post by **Crito** » 18 Jun 2009, 01:18

Yeah, it's in the garage, just in case I change my mind this winter. I always reserve that right.

The saga continues however... so while I'm poking around in that area I notice I'm missing a bolt from the front of the fuse box, and that sound I thought was my driver's side strut was actually the whole box bouncing up and down. Unfortunately to access I'd have to remove air box, which I promptly tore out. And then things got worse.

Long story short, there was some conduit to tranny that had become brittle and in one place where it snaked under another part it was completely missing. Fixed frayed wires... replaced some of that corrugated flame retardant plastic conduit stuff... put air box back together... decided not to put cold air scoop back just so I could watch the vacuum driven thing in air box that open and closes work. Well, it doesn't work! I double checked I had the vacuum hose hooked up right, still doesn't work. So I've been driving around with a hot air induction system all summer!

Grr.... luckily it appears to have gotten stuck in a half open, half closed position, so I was getting some outside air mixed with the hot air from exhaust manifold. Still, I'm so !@#$in' glad I got that thing -- which VADIS says is a "preheating pipe" BTW -- out of my !@#$in' car!

Post by **MadeInJapan** » 18 Jun 2009, 05:01

On the NA 850's (non-turbo), myself and others are just stuffing a piece of tin foil pushed into a ball into that part of the air box to keep the warm/hot part completely closed off. It really serves no purpose unless you live in a cold climate. I wonder if you can't do that with your airbox too and force just the cold side open?

Crito · Post by **Crito** » 18 Jun 2009, 07:15

I dunno, maybe I don't understand how that thing is supposed to work. I push in on preheating pipe flap and air is pushed out vacuum tube. I push on cold air flap and air get pushed out tube too. If I press in either (or both) then plug hose with my finger flaps stay open. So I guess they BOTH open up as the vacuum increases.

Hot air intake.... you'd have to live in Antarctica to think that was a good idea.

Only real downside I see is the maximum depth of water I can now cross is 1' 10", as opposed to 2' 4" with the hose attached, or a reduction of about 6 inches. Up side is more horsepower, lower engine and tranny temps, my cables and hoses don't get cooked, car doesn't break down in Hillbilly-ville, Cleatus and Renfro don't cast me in a leading role in their recreation of the movie Deliverance... and I'm sure there are a few more good reason to just rip that !@#$in' thing out.

BoomerSooner · Post by **BoomerSooner** » 21 Jun 2009, 23:25

LOL Crito...quite the story there. Even got in a Deliverance reference. Impressive!

Gonna have to check my S80 for that thingamajig now.

Crito · Post by **Crito** » 24 Jun 2009, 19:03

The remaining whir sound is coming from AC compressor clutch. Not sure why it's so noticeable ~1900 RPM, but doesn't make the sound if I don't turn AC on, so pretty sure that's it. Still really glad I removed the preheating pipe though.