Replacing water pump - what about idler pulley?

You are in there anyway so why not replace it to be on the safe side. For me, I'd hate to do that work and go back in there 6 months later to replace a pulley.

 

The absolute failure mode would be bearing seizure which would result in it throwing or destroying the belt. The way that you'd know it is going bad would be noise (high pitched bearing squealing at first, harsher, more grindy noise later). Given the isolation of the engine compartment from the cabin, you'd probably notice it as reflected noise off of buildings or other vehicles. The noise can continue for a long time before the pulley seizes though. Listen under the hood every 6 months or so and you should be good.

- Chris

 

Bosch is as good a name as any, though I don't usually think of them for water pumps.

 

1 - Replacing the idler pulley is really REALLY easy on the Prius. About 5 minutes - you don't have to mess with the water pump or the belt.

2 - The thing that fails on the pulley is the bearing. That bearing is a 6301 size bearing - really pretty stout for what it does. If you're handy, you can simply replace the bearing - for example: 6301-2RS Bearing 12x37x12 Sealed Ball Bearings

3 - If you simply replace the bearing, it will cost you ~$10 for a high quality bearing.

 

OZ- I replaced the water pump in our '06 last year. Not a difficult job but it does require you to get into some tight spots. You should take off the pulley to gain easier access to the water pump anyway, so i say change it while you have it off. I would also recommend changing the thermostat while you're there for <$15 and the serpentine belt(if you haven't changed it yet). Oddly enough the pulley is the most expensive replacement part in this group. As for the Bosch water pump it is probably just as good as the original. I think you be amazed as I was about how small the water pump actually is. I took pictures of the process when I did the water pump replacement with the intention of putting a sticky on the site...but life has gotten in the way. I will make an effort to get it done in the next day or so.