OEM coolant vs aftermarket.

I use the aftermarket stuff from valvoline for about $12 a gallon. No ill effects on any of my cars

 

The original coolant in your 2005 Prius was Toyota premixed (pink) super long life coolant. Toyota says that it is good for the first 100k miles of use (when you have to change the coolant in both loops). If you stick with the pink Toyota coolant, you then have to change the coolant in both loops every 50k miles. If you use the red Toyota coolant (needs to be diluted 50/50), Toyota says change it every 30k miles (all of this information is in the Toyota manuals). You should also consider changing the water pumps (there are two, one for each loop) at 150k miles as they have been known to wear out. I stuck with the original Toyota pink coolant for 12 years and 288k miles in my 2004 Prius and had no cooling system issues and saw no reason to use a different brand (Besides, I was lazy and let the dealer do the drain/refills for me and they sometimes had problems bleeding the air bubbles out of the systems).

JeffD

 

IF........you are THAT concerned about a couple of dollars difference in the cost of coolant.......then don't consider changing it until near to the 100K mile mark that Toyota recommends. That will save you several dollars.

IF......you aren't really concerned about a small price difference AND intend to keep your car past 100K miles.......then pick a number less than 100K and change it using the Toyota coolant.