engine coolant mystery leak

Hi all, Just signed up.

I bought my Prius a month ago and love it.

4 days ago I was driving home and noticed the engine temp light was on. Popped the hood and saw the engine coolant reservoir almost completely empty (Perhaps it can never completely empty while in the vehicle due to the position of the hose). Bought some 50/50 put it in and light goes off.

Yesterday evening, after putting 150 - 200 miles on since last adding coolant, temp and check engine light came on. Popped the hood, reservoir almost empty and droplets of coolant on underside of car, however not dripping on ground. Got Engine code P0117 - ECT sensor. No sign of leakage at sensor. I figured first I'd address the low reservoir issue.

Took off splash shields, found a few droplets between the engine and the firewall (driver's side) and on those plates under the cat. Added coolant, ran motor, and could find no leaks. The reservoir was again almost empty so cycled thru running the motor, letting it cool, and adding coolant. There was a horrible sound coming from the water pump when the engine shut off and the car was still on, but this went away as I added more coolant. At this point I assume the P0117 code came up due to air in the system. Used 3/4 gallon 50/50. Still not seeing any leak.

Checked oil - looks fine, the exhaust heat exchanger had already been disconnected, some condensation at tail pipe but no sign of coolant. Seems like that rules out internal leak

So uh yeah kinda stumped.

 

Thanks for responding. So there are the 2 hard lines that come down to the exchanger, I assume there are supposed to be 2 short sections of hose to connect to the exchanger to make it easy for removal etc. At the end of the hard lines they just looped it back with a piece of hose and pipe clamps, real easy to see and no leaks there. Further up the hard lines there was some dried coolant drip, this is the area where I saw the coolant droplets here and there, between the firewall and the back of the engine, that area that's so frigin' hard to see into.

My other suspicion would be the lines to the heater core, forgot to mention in the first post that I put the cabin temp on high, never smelled any coolant, no window fogging.

 

Good advice on changing the coolant, Thanks

 

Issue resolved...(time will tell for sure)

Drove to work and found some drips on the undercarriage, so when I got home I jacked it up again and was able to see some coolant on a plastic cover on the engine side of the firewall. Removed the metal shelf where the wiper motor sits and could see that one of the lines to the heater core was damp. Removed the hose and discovered the line was partly squished (Lame!), tried to reshape is some. Took the factory clamp off the hose and put it back on with 2 pipe clamps, so far so good.

 

Yeah huh
Or a lazy mechanic

 

Thanks for all the great info guys!