Hey guys, first post here.

I am decently mechanically knowledgeable, however I know nothing of Volvos. I just bought a 2012 Volvo S80 3.2 with 187K miles for $800. I am having a weird noise issue with it which is why it was so cheap. I’ll elaborate, but my best guess is a bad differential.

So here’s the symptoms:

1. While driving normal there’s a constant low rumble / almost kind of grinding noise coming from the passenger side wheel / engine area. You can feel the vibration slightly in the car. To me this sounds quite like a wheel bearing OR grinding coming from the diff, almost like the dif has no fluid (haven’t checked yet) however the symptoms get even more weird which I’ll elaborate on.

1. Applying load (gas) without downshifting makes the sound worst, BUT flooring it makes the noise completely disappear. However after flooring it and letting OFF the gas the noise becomes 100X louder / more brutal, MUCH more grindy. It sounds like something is gonna explode in that scenario.

2. When shifting gears the grindy noise generally stays the same but the noise does shift slightly, probably just due to the difference in RPM. I’m doubting it’s trans related as the trans feels and shifts great.

2. Noise goes away when you coast in neutral (so probably not a wheel bearing)

To me it seems most likely that it’s a bad differential, but is it normal for bad difs to run smooth when flooring the car and also for the noise to become 100x worst after accelerating and letting off the throttle? The noise kind of does tend to get worst / better depending on the load on the engine. It seems with high load on a high gear it sounds the worst, but at a low gear and high load (accelerating) it sounds better or sometimes non-existent. M

When I floor it after it down shifts it almost sounds like something is changing / realigning correctly like a bad bearing finally starting to spin correctly (in the dif I assume or wherever it’s coming from) and then it clears up once I’ve started accelerating hard. Like sometimes I can almost hear a weird hollow worble noise like bad bearings, and then I assume once the bearings are finally spinning from giving it full throttle the sound goes away.

Does it sound like a bad dif? Is it possible to have a bad diff yet it sounds fine under full acceleration (and 10x worst after I stop accelerating) is that a thing with bad difs?

Any feedback? THANKS!

 

The differential is part of the trans and lubricated with the trans fluid. It's not bad.

A common (loud) noise maker in that car - is when the front engine mount (on the front of the engine, right side of car) collapses. (maybe every 75k miles or so) They have a gas charge in them and after it leaks out the vibration of the engine is passed directly to the frame. When you accelerate hard - the engine changes position and may not be rubbing the frame as badly. The "dogbone" mount above it - comes apart and will touch the frame also making noises.

A wheel bearing will typically make more noise turning one direction than the other -

 

Hmm I’d be very surprised if it was an engine mount, I’ve never heard an engine mount make this kind of noise, I mean it is a BRUTAL noise when decelerating after flooring it. I mean I’m not saying I’m ruling it out because you guys know way more than I do, but I wonder if I took a video of it and sent it to you if you’d change your mind. Mind if I do that and you can let me know? I’d love for it to be an engine mount, but man does it sound like a bad diff or something.

Also I briefly did a simple check on the motor mounts when I bought the car, I just revved it in neutral and had a friend look. He said it didn’t move at all, but I should have put it in reverse and then drive to see if it moved rather than just free revving it. Should I be able to see it shift if I do that? Any other way to confirm it’s the motor mount?

 

You will see the motor move when you shift to drive/reverse. The motor won't move in neutral.

I did the same test on an old car of mine when the front motor mount went. Transverse engine so if I popped it in reverse you can see the engine rotate forward.

 

Visual inspection -

There will be a gap between that top plate and the "bell" shaped part of the mount. Not easy to see - might have to remove the dog bone to see it clearly.

Have someone (carefully) power brake the car in drive and reverse and watch the engine move.

Or it takes just a few minutes to get the mount out of the car - (use a floor jack to support the engine)

 

no you guys were both completely correct. I put it in reverse and then drive and the passenger side of the motor hopped over to the next zip code. That makes sense that the sound stops when you floor it as the engine is just being pushed back as far as it can go. Sweet, I’m excited, I’ll swap the motor mounts and should be good to go. I assume I should probably replace all of them, right?

 

The only ones I ever replaced (or saw that needed to be replaced and could justify replacing to my customers) is the rf one previously mentioned and the dog bone above that (if torn) . You can certainly replace stuff you don't need - but that's your choice.

How about just replace the one on the front of the engine (if needed) , and the dog bone (if needed) - and see what happens? Then if still a problem replace what is needed next? Save your money for food, clothing, shelter, etc.

 

That’s exactly what I did, I bought the main one you referenced and the dog bone one. The dog bone was only $45. I am just planning on flipping this car so I’m not trying to replace parts that don’t need to be replaced, but I’m also not trying to sell anyone a pile of junk either haha.

also I can hear a very quiet tick noise that is engine RPM consistent, doesn’t sound super loud or alarming, but any idea what that could be? Obviously I know a tick noise could be anything, even as far as an exhaust leak, but do these cars have a common problem that comes with a tick noise that you’re aware of? The engine itself runs really strong and smooth, but just has that tick noise. Can only really hear it at low RPM.