It looks like the inverter pump on my 2003 Prius has failed, and I am not having a lot of luck finding a replacement that is affordable. Can I use one for a 2004 or newer model? I am thinking a pump is a pump for this purpose, as long as it will fit in the hole and I can tie it down.
I wouldn't. Get the correct part, inverters are really expensive to replace, a new pump, not so much, relatively. 2003 Toyota Prius Parts - Camelback Toyota Parts - Genuine OEM Parts - Free Shipping Free shipping, and if you look around, there's a 3% discount.
The correct pump costs $114 plus shipping here: Water Pump - Toyota (G9020-47022) I think it is a particularly bad idea to use a 2G inverter coolant pump because that pump was the subject of a recall, hence a used pump that you can find on eBay probably is a reject with questionable service life remaining.
I vote for the correct part. The cost of incorrect operation of a substitute is, as Patrick pointed out, VERY high, and I personally would not want to do that job twice just to save a few bucks. Also, spend the extra coin for genuine Toyota coolant for topping off that system. The OEM stuff lasted what, 15 years, so Toyota obviously knew what they're doing...
