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.
While reading your post, I was convinced that the problem would be at the exhaust heat exchanger, until you mentioned at the end that it has already been disconnected. If there is a leak, I would still suspect that it is occurring in that area, given that you have already ruled out a leak in the part of the cooling system that is factory-built. How was the exhaust heat exchanger by-passed? Are you sure that the work-around is completely leak-free?
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.
You could rent that one coolant leak detection Pump from an auto store. Check your oil to see if it’s the head.
Since the ICE engine is overheating, it really shouldn't be driven until the cause of the disappearing coolant if found. (Is it being burned in the engine? Is it leaking somewhere?) It's a 2017, has the coolant been changed? If it hasn't, it's probably very acidic which can corrode the head gasket which can cause coolant to start leaking into a cylinder(s). Regardless, needs to be checked out by a good mechanic ASAP.
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.
It takes a bit of force to squish that metal pipe like that. I wonder what else the previous owner did to the car.
Great job! Definitely keep an eye on her and plan on changing out the coolant and transaxle coolant asap. (It takes the same Toyota Super Long Life coolant) My wife's 2017 was done last summer and it only took a gallon and a half for both. Older Prius' have drain plugs on the transaxle for that coolant but ours didn't but I found two yellow drain cocks next to the radiator and that drained both tanks. (Open up the lids on the two coolant reservoirs, of course, helps it drain faster.) Takes a while to get it all drained out and then refill, place the car in maintenance mode so the engine runs, and fill coolant as it goes down and when after the auto-fans on the radiator have come on twice, you're done! (It does take about 30 minutes for the fan to come on twice so you just have to be patient.) One of those funnels that fit on your radiator works great...I got one years ago and very handy....
Wow, thanks, Mendel! So I almost serviced it the Toyota-way...didn't know to use that 6mm drain plug on the coolant reservoir. I just looked, and my wife's 2017 has it but my 2021 does not. Some older Toyota's have aluminum radiator drain bolts right on the engine but, from talking to experienced mechanics, don't ever touch them...if one breaks it's a nightmare so not worth the risk. (In my Tundra, I just drain as much radiator coolant as I can, drive for a few days, and redo it.)
I followed the instruction to open the engine block spigot, draining coolant on our ‘10, got about 2 tablespoons for my trouble.
