Well, just saying, you do have to take off a few things to do serp belt, which would already be off to change timing belt/water pump, of course it's much smaller job to just change belt. I think it's just the one belt (besides the timing belt).
The thing is, here's a car with 265k miles on it and she asked her dad what was done to it and he said "nothing" which doesn't make any sense because obviously you have to do something to run a car that long. I guess I'd say, the chance I'd be putting in a new serp belt when one was just put in, is like zero.
The whole timing belt thing is happening because one of the pulleys for it was squeaking which tells me, bearing is shot, and you wouldn't like order one bearing and tear the thing apart for that and you wouldn't like squirt some oil in it and say, ok, it's fixed....so... could I get by with just timing belt and bearings, probably, but at those miles it just seems to make sense to do the water pump. She asked me, why replace pump if it's working and I said "I think, if you ask 100 people, should I do water pump at this miles, while I'm doing timing belt, assuming they're both original, 90 or more would say do it." Hope I wasn't wrong there.
Serp belts seem to vary all over the place in price, I like Dayco stuff but no particular reason for it. Not sure what you lose if serp belt stops working; at least the alternator, lol. It wouldn't wreck the engine like broken/slipped timing belt though.
This is a pretty good vid
Timing Belt & Water pump Replacement LEXUS RX300 3.0L 4WD 1998~2003 1MZ FE U140F - YouTube
Taking off the serp belt is early on but you do have to take off a few things.
Yes the setup of the transverse engine puts all that stuff in a kind of cramped area to the side. When I did belt/tensioner on the XLT I was also doing rad replacement and with the rad out, which is easy (and messy) to do, there's so much room to work it's just really nice and one of the things I like about them. Having worked on the Mazda, fairly similar, that was a factor in getting the Ranger.
The whole premise here is trying to make a car with unknown history (except that it was one-owner) reliable so it's balancing cost against reducing points of likely failure and timing belt is one thing you don't want failing because of collateral damage not to mention you lose control of the car maybe at 80mph that can be bad apart from the engine being toast. I could have skipped pump, it adds a lot to the work, on the other hand I'd hate to do timing belt then have water pump go bad a month later and tear it apart again.
To me, let's say it adds 200 maybe parts/labor to do the water pump. Balance that against her calling me from 400 miles away "It's leaking water really bad" and me telling her, drive a little, dump in some water, watch the temp gauge. No thanks. I could be wrong about what I'm doing, but if anything, it's erring on the side of caution.
Edit: hired wrench says get serp belt and also get power steering belt he says there are those 2.