I looked at my coolant overflow and it is way low just barely above the hose that is connected from the radiator, and a good three inches below the low line, it really worried me, so I'm wondering if I can just add some fluid or if I have to completely flush the whole thing. It has 186,000 miles on it and I bought it used with 127,000 miles as far as I know it hasn't ever been flushed. There's no lights or warnings on either.
sounds like there's probably a slow leak in the water pump. Look around the pump and belt area and see if you see some pink/white crusty material. If you see it, it's just dried coolant that's leaked out. You would need to change the pump and belt (since it's out already), then fill with new coolant.
Yes, it's probably a leak at the pump. The coolant should be changed at 100,000, then every 50,000 after that. It does not have to be "flushed," just a drain and fill. This is actually a difficult process requiring a special Toyota tool and coolant, so be sure anyone you hire to do the work is qualified. It does not necessarily have to be the dealer--in fact, many DIYers can do it. Well done, finding the problem in time, before air got into the system. If you cannot get the leak found and fixed right away, at least fill the reservoir with the correct coolant. But it sounds like the car is long overdue for service.
I will be a bit less gloom and doom than others here.... It is entirely possible that there really is no leak of significance -- not likely -- but possible. First, as suggested, check around the water pump pulley for white or pink deposits. I you see none or barely any, your water pump may be O.K. This is a bit controversial, because some people suggest a tiny bit of deposit is O.K., while others say none should be visible. If you see a lot, -- I assume you are not able to do the work yourself -- it is a trip to the dealer or another mechanic for a new pump -- around $500-$600. If you don't see any and after looking all around the engine compartment you do not see other leaks, you could just try to refill the coolant. Buy REAL Toyota coolant only (the dealer will have it) that is meant for the Prius. Fill the plastic tank and then remove the big black plastic cover that covers the metal radiator cap and remove that cap and fill the radiator itself, if needed. If you have no idea what I am talking about, google the terms, check out YouTube etc and look for instructions, pictures and videos. If I knew where some might be lurking off-hand, I would direct you to them. I don't. But, there are lots of posts here on PriusChat that would answer those questions. So, you might be able to get by with just adding coolant -- might -- around $25 for a gallon of it at the dealer. And, of course keep a very close eye on the coolant level -- like daily for a couple of weeks at least. You might get lucky and get out for only $25.
And if you now have extra coolant, there is another system for the inverter, check the level of that system as well.
