06' t5 diesel is gradually getting louder

[boscoj]

I've had my xc90 for the last four years, all trouble free but now the engine has been developing a louder, higher pitch. The low warble has been replaced by a cutlery drawer. It's not noticeable inside the car. It's when you hear it as it's being driven past you at low speed.

There has been no loss of power but the mpg has gone from 34 to 30.5 in the last month. Any idea of things to look at first?

[boscoj]

Just looking through other threads here, I might check the alternator bearing first as it fits the sound I'm hearing.

[tonygreen1966]

Does it disappear when you switch on the aircon? If so probably the freewheel /clutch on your air con pump. Check by removing belt and seeing how freely it turns. Mine went, ancillary belt got hot and melted the plastic tensioner pulleys and the plastic PAS pump pulley then snapped the belt. Luckily it never pushed bits of belt into the timing belt casing and snapped the timing belt. New belt, PAS and Aircon pumps, new tensioner and 'while I was down there' I changed the alternator pulley after reading various problems on here about it. Got the aircon pump from ebay-£120 me thinks- 8 months later so far so good. I also spent about £40 on aircon dryer(ebay £40 I think) and about £40 on air con o rings(dealer) for all the dismantled connections as I didn't fancy paying £60 for air con refill and it all leaking out.

[boscoj]

Thanks for your reply.

In my case, the aircon does not affect things but I'll still bear what you've said in mind as I go through the possible causes. It sounds like a worn bearing of some kind.

Thanks again, B.

[GSTheo119]

I just sorted the alternator pulley bearing and learned this - If it is the pulley bearing, open the bonnet while running, you can detect the source of the chatter coming from the aux belt area - the alternator's at the front and top, so if its not obviously coming from here then I doubt that's you problem. Useful to watch SiiRobbs Youtube vid on this for more info. He is testing for a failed clutch, though in my case the clutch mech worked fine and it was turning OK, there was just a small amount of lateral play which must have been enough to make that noise, especially when cold. You should be able to test for lateral play with the aux belt in place but it'll be hard to test for rotation resistance otherwise. If you have a Tork60 socket and long handled ratchet or extension (its a powerful spring so needs leverage) you can pull on the tensioner and just loosen the belt to test your pulley rather than fully remove it. (getting that Torx in can only be done by feel unless you remove the wheel and peel back the wheel arch liner.)
BTW If it is your alternator pulley and that's what reduced your MPG I wouldn't drive it until fixed as it must be dragging the engine suggesting imminent failure of something.

[owenfackrell]

The tensioner and idler pulley bearings can go bad and make this sound as well as the alternator pullley bearing. If you are taking the belt off to check the alternator i would check all the others at the same time. The idler pulley is available form euro car parts for less than Volvo and is the same make (IPD from memory). I don’t know on the tensioner one.

[boscoj]

Thanks for those suggestions. Once I have properly diagnosed the problem, I will let you know.

[boscoj]

Problem solved. It was the torque rod on the mount that joins the engine and gearbox.

[Harley Dave]

Thanks for the update - always good to hear what the problem was (and the fix)

Cheers

Dave