Coolant leak.. can't find the culprit. Please help!

There are two cooling loops, one for the ICE and one for the inverter and transmission. They use the same type of coolant. If the car is losing coolant it should be obvious which one is the culprit in that either the radiator/overflow tank loses fluid (check both) or the tank next to the inverter does.

If it is the ICE loop go to an auto parts store and borrow a radiator tester. It attaches to the radiator neck, you pump it up to some pressure, and see if it holds. In this case we might expect instead for coolant to spray out wherever the leak is that deposited the fluid in that video. Be very careful to not put much force on the radiator neck when attaching and using this tester as it is somewhat fragile. Breaking that off will make your problem a lot worse than it is now. As long as you have that tester also test your radiator cap, both that it holds pressure and that it opens at the specified pressure. Caps do go bad and it would be silly not to test it if you have the right tool at hand.

The inverter coolant loop isn't pressurized like the other, so you won't use the radiator tester there. That coolant loop is much simpler. You might look at the inverter pump, which is pretty close to the transmission. In fact this is the loop that cools the transmission. Follow the hoses up and down from the pump. Do a little search and you can find the hose diagram for this circuit, it is much (much) simpler than the other one.

 

That's what I would be looking at the big hose coming out the head that crosses kind of sort of right over the transmission or it's connection to the engine and then heads to the radiator that would seem to be a hose that Might could become permeated pretty easily. Mine's not leaking from there but it would be a good place it looks like mine is still the factory original hose at 500,000 mi and it's still black it's not turning white it doesn't make any odd noises when you squeeze or twist the rubber so it stays for now leaking down from 25 to 22 that's 3 PSI that's going to be tough to see especially if it takes 20 minutes that almost seems like it's internal going into the engine but let's just thinking out loud where it's a very small t90 little hole in a hose that may be only opens at pressure and hot pretty wild of course you kind of know it has to be some of the hosing that's crossing over the engine transmission connection at least and the water running down on the transmission side of the connection which will allow it to pull in those wells of ribs and casting. There are only a couple of hose once the inverters moved out of the way the hose that goes from the three-way coolant control valve along the inverter pump and up to the little pump for the heater could be the hoses that go out of the inverter pump and so on You might just replace those that's like 5/8 heater hose maybe when you lift up on one of those and disconnect it you'll get a hand or a swipe of coolant on the bottom of your hand from the bottom of the hose that you really can't see until you lift the hose up flip it over or something while taking it out of the car.

 

Well I mean those three hoses are like probably a whopping $28 or something from Gates or any of the superior hose manufacturers Victor reins etc . When I had the inverter flung to the side I'd probably just replace them and look over the hose that crosses over the transmission sort of that goes up to the pump on the firewall amid ships of the brake parts or even that pump leaking from its housing or from one of the barbs on it that could kind of run right to the spaces on the transmission you're speaking of although I've never seen it when I'm doing the break actuator I always look over those hoses pretty good and if I see anything that looks any kind of way just change it hoses are cheap.

 

The coolant control valves and interesting animal but when it fails I guess it fails closed or something so what fubar the heat . It looks like you can just open the cover up I did that and move the thing over to open it and then well it would stay open and make the heat circuit be open and heading to the pump all the time even if it's not on and those hoses I guess they could leak at their connecting fittings but that's down at the thermostat housing then at the control valve and then from the control valve through that s-shaped hose up to the pump and then there's a fitting on the bottom I think that goes to the transmission or the forward edge of the transmission but you can't leave it unplugged or you'll have a code but you may have heat I wonder what would happen if you made it so that the valve would never close I guess the engine might run cold or something I don't know doesn't seem like it would It would just keep the passages open all the time so the heat would be made regardless and then if you don't want the heat when you have it system set on low I guess the damper door is closed and you're getting outside cold air or you have the air conditioning on getting cold air

 

There may be air pockets in that coolant loop now, which would explain the lack of heat and possibly the odd temperature readings. This vehicle is notorious for hard to remove air pockets.

To eliminate the splattering problem, maybe some sort of shield or drip redirect could be temporarily bolted on so that coolant doesn't land on the spinning metal?

Regarding the hose cost, check on RockAuto or another reputable car parts site. At this moment they have 4 of the cooling hoses listed from Gates at around $15 each (plus or minus).

2008 TOYOTA PRIUS 1.5L L4 ELECTRIC/GAS Coolant Hose / Pipe | Shop Now at RockAuto

 

With the motor off, and that tube attached to the bleed valve, attach a fluid transfer pump to that tube and pump outwards until fluid starts coming up the tube. If fluid comes up immediately that supports your "no working pump" hypothesis. If it comes out never, and the tube collapses, then the bleed valve isn't actually open or is blocked somehow. If it comes out after a while and the level in the radiator neck drops top it off there and try your experiment again.

 

Look carefully that's predominantly 5/8 heater hose there are all kinds of 5/8 heater hose that you can bend in any of those lazy bends that are on the Prius they're not tight enough to have to be perfectly preformed If you have the hoses off the car and you go to advance Auto or Menards they let you in the back of the store where the hoses are hanging you will find the hoses you need a slight trim here and there and they're clamped on and working fine and they're made by a major manufacturer like Gates yeah I just said $28 but okay I'm not going to spend $42 a hose that's not going to be any need for that If you think about this for about 5 minutes you will see where the bins you're looking at and say the hoses that are connecting to the coolant control valve those are standard bent hoses you see them hanging up on the wall in a part store if you're into that sort of thing some of them are really long You're going to cut off a foot of the hose Just save it You will use it someday well maybe you won't. But I'll get around to it so you should be able to skin that cat pretty easily and obviously if you don't see anything leaking with 23 lb of pressure and the hose is pumped up like basketballs probably not anything coming through that piece of rubber It's a good bet. I don't have anything coming through any of the pieces of rubber connected to the cooling system of any of the four Prius that I own but I have an '09 that randomly loses a few cups to almost a quart of water seemingly in a 45 or 50 minute drive right around the neighborhood and the heat is very wonky when I fill it full I will get some heat very little The far right vent on the dash is always cold I didn't even know there was any weird ducting like that I haven't looked The center vent to the right of the radio is the hottest the one to the left of the radio is 20° cooler I haven't even messed with the far right then so above where I said the right vent I meant the left the one on the American driver side is ice cold I don't have any reason to believe it's the damper door because when I fill it up and I do start to get heat when it starts to go cold nothing's moving It seems the air temperature is just gradually going down like I'm moving the temperature setting button from 85 to 71 or something but nobody's touching anything nothing has changed and then all of a sudden I'm blowing cold air out of all the vents and if I go home and park the car don't crack anything let it sit about 2 hours it'll still have pressure in the radiator like basketball hardness but the air has worked its way up to the top and if I crack the radiator or crack the lever vent on the cap real slow I'll let air out the tube and no water and then when the air is completely out of the system and I take the cap off I see no water in the neck I squeeze the hose with my ear near the neck and I can hear the water right at about level with the neck but can't see it then I start adding water and air bubbles start dropping the water down the neck and I'm sitting here pouring this quarter inch stream of water trying not to spill it over the neck for about 25 minutes and I wind up putting about a quart or a little less in and then we repeat the whole process again and then the heat will just start blowing cold mid-drive I like come to a stoplight and it'll be hot and then as I get ready to leave the stoplight all the air is cold coming out of all the vents I also noticed my windows are fogging up a lot more but I have no wetness on the carpet and I have no reason to believe that coolant is escaping the heater core and blowing vapor in my car fogging the windows but it sure looks like it and then again this is a '09 with 550k mi on it so I'm expecting all this I can't wait to see what it does in the summer because this car has ice cold air conditioning and has never overheated in the summer and I mean never but it's done this weirdness in the winter before I have so many cars I just usually leave it to the side and drive it all summer with the air on full blast.

 

Use water to wash all that old fluid away. Blow off the water puddles or whatever to dry it out the best you can. Grab a roll of paper towels, pack that area full of paper towels and run the engine for a while. Afterward running engine a while, start removing the paper towels until you see where they're getting wet from coolant. That should point you in the right direction, so you don't have to guess. If needed, pack the heck out of it and take the car for a drive, then start pulling them out for inspection.

 

Another cheaper option would be to get a borescope/endoscope and run it into the engine compartment somehow. For an example of what I mean, go to Amazon and search for B0CF1VCDBD. This one has a front view and side view camera, but you can only use one or the other at any given time. Note, you must use a USB C phone. I have two of these scopes from different manufactures and a USB Micro phone and they work like crap through the adapters, but work fine on my son's phone with a USB C socket. (That might also be a function of how powerful the processors are.) As a bonus, these are great for probing around in nooks and crannies, or looking in cylinders.

How to get the camera end into position from inside the car? Thinking. Ah, maybe pull back the carpet in the front passenger foot well to expose the drain tube for the evaporator. Pull that back and push the camera through there and then around to the driver's side and up. The hose comes out over some structural member, so you won't see it easily from underneath, but reach around the top and you can grab it. Just don't turn on the A/C in any mode or that hose will pee all over wherever in the car you left it. Which suggests you probably want to wait for a warm enough day so that there is no need for defrost.

 

OK. Maybe before recording data on a real test run a thin tube into the target area, close the hood, and drip a little coolant through the tube to verify that the camera can see it.

The endoscopes can take long movies too, it is just done on the phone end rather than in the device itself.