2019 Prius Slow Coolant Leak

Discussion in 'Gen 4 Prius Care, Maintenance and Troubleshooting' started by JeffPGH, Jun 25, 2026 at 3:51 PM.

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  1. rjparker

    rjparker Tu Humilde Sirviente

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    Sounds like just the ac and fans were running at first then the rattle on engine startup.

    But you are losing a lot of coolant in one day. If it was coming out at the exhaust heat exchanger I would expect some steam soon after the exhaust heated up.

    With that much coolant loss the combustion leak detector test might be an easy test without having to remove the windshield wiper assembly to access plugs.

    IMG_1951.jpeg

    Any shop could do that test as well.

    If it is negative, you could do the exhaust heat bypass or move straight to a borescope test with the specific setup as described in item 2 of post 16 and as demonstrated in the videos.
     
    #21 rjparker, Jun 28, 2026 at 3:58 PM
  2. JeffPGH

    JeffPGH New Member

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    I have a few updates.

    I did 166 miles yesterday after I filled it up in the morning and when I checked it this morning it was right at the low line.

    I was at the dealership today for my complimentary oil change and I spoke with the guys there. They said the overnight pressure test they did included looking at the engine with the borescope. According to them it looked good. However, they did say that when I’m running it and it’s getting hot it might possibly open up a small crack and start leaking. They said it would never get that hot here in the shop. Since I’m coming in soon (in about a month) for my coolant flushes he said I could try the stop leak stuff to see if it helps and anything left in there would get flushed out during the flush. I figure the stop leak stuff is kind of a last resort right? I don’t really want it to risk it messing anything else up. How safe is it to use? Also, while they’re doing the coolant flush I’ll have them do some tests on the water pump and check it out.

    I was thinking my next step would be to try the combustion leak test just to see if that does turn up anything or not but It probably won’t if they did a good job on the borescope test. If that doesn’t show anything I was thinking about doing the bypass just to confirm 100% if it is the new heat exchanger pipe or not.

    Does that sound like a good plan?
     
    #22 JeffPGH, Jun 29, 2026 at 12:12 PM
  3. Brian1954

    Brian1954 Senior Member

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    What was the engine coolant temperature during the trip?

    Do NOT use the stop leak. That is something you use as a last resort
     
    #23 Brian1954, Jun 29, 2026 at 1:16 PM
  4. bisco

    bisco cookie crumbler

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    just before you sell the car :D
     
    #24 bisco, Jun 29, 2026 at 1:37 PM
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