Belt tensioner, idler pulley and belt replacement ?

For prevent maintenance what mileage should these parts be replaced?
I'm at 108,000 km (67,000 miles), no sign of any noise so far, I will remove belt to check sound of bearings in pulleys, however, it is very tight spacing between the radiator and belt to work.

I can't tell you when you should swap your idlers out for new ones, but, here's a cautionary tale from last weekend:


I bought a Q7 with 220,000 km's on it a month ago. Last weekend we went for a road trip from BC to Idaho to have a little play in the casino. I won US$2,300 from a $100 stake, and was real happy during the drive home.


That's when one of my idler pullies decided to 'disappear'. Like, vanish!



Late at night and right in the middle of nowhere, as well as -10deg C. Got a taxi back to town ($250 and 3 hours ordeal), hired a rental car at the airport to run around in ($50), hotel for what's left of the night ($100), tools to replace the idler, plus contingency items ($100), and a new idler ($15) and belt ($36).


So, so far I'm out $540 and counting for a $15 part. My wife lost a day's wages, and I had the cost of gasoline for the rental car to factor in.

In reality, let's call it $900 for the sake of a $15 part.


It took me about an hour to fit the new idler and serpentine belt. The old belt was fine, but I replaced it anyway. I nearly got frostbite on my fingers, but the job itself was easy peasey lemon squeezy. BTW, there's plenty of room between the radiator and the idlers. I had no issues, and I have large hands.



The only difficult part was a undoing a 6" metal bracket that runs from the bottom of the engine block, around the belt, then back to the block. It has a wiring harness atached to it, which had to be disconnected all the way to, and including, the 2 sensor plugs. The plugs were a bit of a ***** to get off, I must admit.

What a pain in the arse!! This would have been a simple task if I had access from underneath. I was only able to reach the top fastening of the bracket and unscrew the torx screw. After that I just bent the bracket out of the way and fed the new belt on.


Yesterday, I renewed the 3 remaining idlers!

Joe, sorry to hear of the part failure and the pain and cost it set you back. Do you recall if you heard any unusual noise from the idler pully?

I think you were lucky that the failed idler did not do any other damage. However, it sounds like Lady Luck was on your side on that trip to some degree.

Sounds like a lot more room to work on the Q7 vs the Q5 as I think I need to remove the front bumper fascia in order to move the rad carrier forward to gain access to these parts and I'm not quite 100% sure how to do this yet but researching the method on the web.