Overheating only at high highway speeds

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Hitchhikin Taz, Dec 29, 2020.

  1. Hitchhikin Taz

    Hitchhikin Taz New Member

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    I get the red overheating signal at high end speeds of 80+mph. It turns off after I slow down to about 60 and won't turn on again unless I get back to 80+. The coolant has depleted slowly and I've topped it off every couple weeks. It's worse when the weather is colder.
    I used a coolant pressure test and it maintained pressure at 16psi. When I pushed it up to 20psi, it would slowly loose pressure. I wasn't able to see any obvious leaks. Under both circumstances, it would oscillate roughly .5psi up and down (not sure if that's normal).
    Thoughts on the dilemma? Head gasket issue seems to be the biggest fear.
     
  2. tankyuong

    tankyuong Senior Member

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    Head gasket for sure
     
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  3. rjparker

    rjparker Senior Member

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    Start up rattle ever?
     
  4. Pluggo

    Pluggo Senior Member

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    In this case, no visible leaks suggests that you're blowing antifreeze through the exhaust system.
     
  5. ASRDogman

    ASRDogman Senior Member

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    If you drive the speed limit, it's less likely to overheat. :)
    It also sounds like the head gasket is going. Pull the spark plugs and do the pressure test.
    Listen to each cylinder, and look for coolant on the pistons.

    You may also have a water pump going bad....
     
  6. Hitchhikin Taz

    Hitchhikin Taz New Member

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  7. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    How many miles?
     
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  8. ASRDogman

    ASRDogman Senior Member

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    I forgot to ask that. :)
    I had meant too, but was interrupted....

     
  9. Hitchhikin Taz

    Hitchhikin Taz New Member

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    220k miles. No rattle on startup. Is it normal for the psi to oscillate at higher levels?
     
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  10. rjparker

    rjparker Senior Member

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    I think there should be a new forum just for Gen3 Head Gaskets. A couple of stickies for Symptoms, Diagnosis, Repair Options, How Long Did Sealant Work and of course, Root Cause Theory of the Month. Extra points if your engine now has a hole in the side. Meetups to include White Smoke and Severe Rattle contests. Winner gets a JDM engine.
     
    #10 rjparker, Dec 30, 2020
    Last edited: Dec 30, 2020
  11. Grit

    Grit Senior Member

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    Great suggestion. We also have to figure out better ways to keep non gen 3 users from posting non gen 3 stuff on this sub forum.
     
  12. Grit

    Grit Senior Member

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    by what?
     
  13. Grit

    Grit Senior Member

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    A poster once posted if your driving the speed limit, youre blocking traffic. Actual speeds are 5-10 mph faster than posted speed Block traffic or overheat your engine :ROFLMAO:
     
    #13 Grit, Dec 30, 2020
    Last edited: Dec 30, 2020
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  14. ChapmanF

    ChapmanF Senior Member

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    I've found that to be one of the things that can noticeably vary between regions, or even between highways within a region.

    When I was in the Detroit area, I noticed each highway kind of had its own culture. I-275 northwest of town is where you pretty much had to hit 10 or 15 miles over by the end of the entrance ramp or you'd just never successfully enter.

    Ford Fwy in midtown was where entering drivers never believed in merging. Every rush hour it would be brought to complete standstill by entering drivers racing around each other to the very end of the ramp, having to stop, and then stopping everyone to horn their way in. Occasionally a commercial truck driver would pull to the right to block one of them and it was a beautiful thing.

    I've noticed regional differences in the advisory speeds (yellow signs) for upcoming curves also. Where I am most used to driving, midwest and east, they are conservative; with good weather and dry pavement, you can usually assume 30 or 40 percent higher (percent, not MPH!) will be perfectly comfortable.

    Find a similar curve advisory on, say, 17 north of Santa Cruz, and the advised speed pretty much means what it says.

    I've also found a large effect of driver perspective. I had a significant shift of driving habits in my early 30s, from being a habitual speeder (it was kind of part of my identity) I sort of went cold-turkey and often set the cruise right at the posted limit. What I've noticed in the years since then is there are usually some people passing me (no problem, that's why they have lanes for that) and also, sort of amazingly, still quite a lot of people I pass (again no problem, there are lanes I can use for that).

    Back in my always-a-speeder days, I would probably have sworn up and down that I was necessarily keeping up with traffic and it would be crazy to drive the limit, with every other driver blowing my doors off. That honestly was how I perceived it at that time. It was kind of eye-opening to see by how much I had misperceived that, once I was driving nearer the posted limit.
     
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  15. Mendel Leisk

    Mendel Leisk Sunday driver DIY’r

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    I keep thinking of a hospital emergency department:

    “Engine shaking and losing coolant? Take a number; the waiting room is over there.”
     
  16. TheLandYacht

    TheLandYacht Junior Member

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    There are large segments of highway out here in Central Texas where 80mph IS the speed limit...the actual, honest to goodness official speed limit. And you'll STILL get passed like you're sitting still.
     
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  17. Attila Fekete

    Attila Fekete Member

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    I was always wonder why the speed limit is so low in the US. Everyone is driving, car seems to be part of the culture - as I see it from here. In Hungary we have cars that can pass 80 mph only in the last 30 years, but that’s the speed limit for quite some time.
    (And hardly anyone goes below 90 mph.)
     
  18. Hitchhikin Taz

    Hitchhikin Taz New Member

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    Sealant? I'm still looking for solutions here.
     
  19. ASRDogman

    ASRDogman Senior Member

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    Because people don't know how to drive at those speeds.
    But they think they do.
    And when there is a wreck, it's horrible and usually involves dozens of vehicles.
    I saw that in germany...

    Plus, it's a control thing. If there is no speed limit, how will the highway patrol make any money?


     
  20. ChapmanF

    ChapmanF Senior Member

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    To say nothing of that air drag following the cube of velocity thing.
     
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