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How to troubleshoot a loss of coolant?

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by JStrenk, Apr 16, 2024.

  1. JStrenk

    JStrenk Active Member

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    I have a 2016 Prius that has been absolutely flawless for the 5 years I've owned it since my 2010 was Totaled.
    I haven't been driving it lately since I bought a Maverick Hybrid and so I lent it to my daughter to use. I needed it back to get it e-check and change out the snow tires.

    While driving it one morning after it getting checked, I notice the heater wasn't working and I thought that maybe there was trouble with the blend valve was sticking. Looking at the temp gauge on the scan gauge was at 186*F to 190*F. so why was I not getting any heat?
    Remembering one other time I had a similar problem on an older car, I checked the coolant level and it was empty. I added more coolant once and then a little more to top her off. That works out to be about 1/2 a gallon. The heater was working great again and engine temps were still at 186*F.

    There are no spots of coolant on the garage floor or any smells inside or around the the engine.
    Seems to be loosing about 100 milliliters (1/2 cup) every 60 miles.
    Oil level is normal, still clear cause I just changed it about 400 miles ago.
    90,000 miles on the engine.

    I do have an off and on problem with the radiator shutters. I already replaced the broken shutters but I get a warning message saying they are not moving every once in a while but shutting off the car and restarting it clears that problem. I already replace the broken shutters about a year ago.

    The engine run flawlessly and still giving me around 60mpg. Acceleration is great. No warning lights or anything.

    I have a OBD2 scanner.
    Coolant system pressure tester,
    Compression gauges, leak down gauges.
    All sorts of tools to get in a lot of trouble.
    I will look to see if there is any steam coming out the exhaust but if it just a leak, will it het hot enough to turn to steam so I see it?

    What I don't know:
    Where to look for leaks or even see it if it's internal to the heat exchanger.?
    How to crank the engine to get a compression test.?
    How easy to replace the heat exchanger?.
    Can I bypass the heat exchanger temporarily?.
    Why did this just start? From sitting around to much? .
    Is this possibly just the cooling system re-leveling itself because it ran so low on coolant.?
     
  2. vvillovv

    vvillovv Senior Member

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    How long ago did you add the 1/2 gallon of coolant?
    What's the coolant level look like now?
    Possibly .... keep checking the coolant level ...
     
  3. JStrenk

    JStrenk Active Member

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    That would of been 2 days ago.

    I was looking for wisps of vapor coming from my exhaust pipe but the engine doesn't run long enough to see any vapor.
    I felt along inside the tail pipe to see if it was wet and it was but it didn't look (clear), smell (no smell) or taste (no taste) like antifreeze.

    Am I wrong in thinking this is just to heat the engine up faster so it runs more efficiently?
    I may bypass it until I can afford a new unit.
     
  4. Mendel Leisk

    Mendel Leisk Luddite

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    you’re presumably referring to the Exhaust Heat Recovery (EHR) system? It’s a common cause of coolant loss with Gen 4, due to defective component. Toyotas offered to replace for free; check with your dealership. There’s a hitch though: the (pricey) EHR component and the (very pricey) catalytic converter are one part, and (conveniently?) in short supply.

    A further hitch: dealerships and Toyota will (also conveniently?) refuse to do anything other than full replacement, say a bypass of the system, since it’ll compromise a pollution control component. And they won’t do the full replacement because the replacement part isn’t available.

    maybe supply issues are loosening up, again check with dealership, but don’t get your hopes up.
     
  5. Doug McC

    Doug McC Active Member

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    Just out of curiosity: has the coolant ever been changed yet or tested lately? Just for my information.
     
  6. vvillovv

    vvillovv Senior Member

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    Is that a calculated amount of coolant loss based on the 1/2 gallon of coolant you refilled two days ago? or have you been watching the coolant level since more than 2 days?

    If it turns out to be your worst nightmare leaky heat exchanger and you caught it early and it didn't overheat, you're golden, the bypass is an easy fix.

    Jiggle your muffler ... hear coolant in there? `1/2 gallon coolant loss might not be enough of a loss to make it back that far ( to accumulate in the muffler ), yet, if it is a heat exchanger leak.
     
    #6 vvillovv, Apr 17, 2024
    Last edited: Apr 17, 2024
  7. JStrenk

    JStrenk Active Member

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    Latest update. Cooling system has held 15psi for 20 min now.
    How long should I let it go for ?
    IMG_4129.jpeg
     
  8. BiomedO1

    BiomedO1 Senior Member

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    I don't see how your passing a coolant pressure test, if your losing 1/2 gallon every two days.
    The most likely defective part is the EHR. There's a TSB out on it, so see if your dealership will replace it for free. If not, bypass it and check the coolant levels for the next few weeks. If the level remains constant, Problem solved.

    Good Luck....
     
  9. JStrenk

    JStrenk Active Member

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    IMG_4133.jpeg Sorry for the miss understanding. It’s not loosing 1/2 gal everyday. I put in 1/2 a gallon when I first saw it empty. The I’ve been adding 1/2 cup last couple of days.

    I extended the pressure test. Looks like 1 psi drop in pressure in 2hours and 20 min
     
  10. a2058

    a2058 Junior Member

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    When I changed the coolant a while ago, it did take a couple good runs to settle out and ended up topping up. But after that, it has held rock steady at Max line. Try going up a hill while accelerating hard and ICE engaged. If you get smoke out of the tail pipe under that kind of load, it’s likely coolant burning out of the exhaust. Mine doesn’t do that but the other day I saw another gen 4 do exactly that, which was quite sad to watch…
     
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  11. JStrenk

    JStrenk Active Member

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    Well I went to work today about 50 miles. Finally saw the steam coming out the tailpipe and when I got home I found the coolant level had dropped about 1/2” in the tank.

    so I hooked up my shop vac and got to work. It took longer to get my tools together than actually performing the bypass.

    why a shop vac? Loss very little coolant. As you can see in the picture.
     

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  12. BiomedO1

    BiomedO1 Senior Member

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    LoL, that's usually the way it goes. A 10 minute job takes a half or a full hour to find tools and clean-up afterwards.
    May sure you check the coolant loop every time you change the oil. It get hot next to that exhaust pipe, so that hose may burn a bit. Just give it a slap, once in a while to makes sure it isn't falling apart.

    Nice work....
     
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  13. sylvaing

    sylvaing Active Member

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    Any specific reason you went from under the car instead of under the wiper cowl?
     
  14. JStrenk

    JStrenk Active Member

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    Just because I didn't fully understand what the cowl one was doing and the one underneath was pretty simple.
    Maybe after doing a further investigation I may switch to that one.
    I procrastinated too long about the pressure test and I had to do something that day as my daughter was getting it the next day.

    Good news is 200 miles and not a drop used.
     
    Mendel Leisk and sylvaing like this.
  15. vvillovv

    vvillovv Senior Member

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    About the cowl bypass, I'd think the undercar bypass should show results quicker after the bypass since the coolant in the lines will leak into the exhaust until they are leaked out.
    Unless the coolant lines under the car are drained before or after the cowl bypass.
    It appears to me (thinking about it) the undercar bypass is more effectively fixing the issue faster than the cowl bypass, even if it seems less convenient or more work, initially.