I am planning to change the water pump on my car because its leaking. I do plan to change both belts as well. Should I also change out all the pulleys and tensioners. I don't like replace parts for the sake of replacing parts because that means the old part needs recycling, etc, etc. Let me know what you all think. I realize there is a small additional cost for the parts. Give me some advice. What else should I change during this process?

The car has 150 k miles.

 

You could swap out the idler and the tensioner if you wish. However, if they aren't making noise you can probably leave it. They will start making noise long before they fail, so they should not surprise you.

 

If it were me, I'd replace the tensioner while everything is in bits on the workshop floor. You don't want to be diving in there again any time soon. However, it you need to save the pennies, (or dimes !), just leave the old one on.

 

The bearing in the idler pulley can be replaced while things are apart.

 

Hi Tim,
My SV8 at about 193,000Km had growling noises at idle when I bought it. Some months later I could feel the car hesitating, and the noise was worse.
I ended up changing the two bearings in the accessory belt idler and tensioner, and the two in the supercharger belt tensioner and idler. Cost of the bearings was about $NZ 70 (approx $US 40). I used a small press and appropriate sockets to press the old bearings out and the new ones in. Solved the noise problem, and the car seemed to run much better. The thread that was most useful is:
https://www.jaguarforums.com/forum/x...acement-65171/
SeanB gives the exact bearing numbers and procedure for changing them. Well worth doing at your mileage. You do have to remove the coolant tank, but you will be doing that anyway for the water pump.

Hope this helps
Pete