Bypassing Heat Exchanger

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Jacob Bonner, May 5, 2021.

  1. Jacob Bonner

    Jacob Bonner Member

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    Vehicle:
    2012 Prius
    Model:
    Two
    I've not seen this specifically discussed here, but how does one bypass the heat exchanger? I'm having overheating issues and I've replaced pretty much everything else in the cooling system, and bypassed the heater core and it is still overheating. Bypassing the heat exchanger is my last idea, but I'm not exactly sure how to do this.

    Do I bypass it at the aluminum pipes underneath of the hood, or should I bypass it closer to the heat exchanger itself, underneath the car? If anyone has a PDF of the coolant system that would be nice so I can get a good idea of where the coolant is going and if there is anything else it is cooling beyond this.

    Edit: the irony is that once I bypassed the heater core the other day, it drove perfectly fine for about 30 minutes. Once starting up the car again, it was back to overheating. It really makes no sense to me. I really thought I fixed it. I took it to the dealership some months ago and they were essentially useless in diagnosing the problem. They just wanted to replace every part that I had just replaced, $500 a part. I wasn't about to do that.

    Water pump (replaced twice)
    Thermostat (replaced three times)
    Radiator (replaced)
    Both radiator hoses (replaced)
    Coolant reservoir (replaced)
    Bled air (multiple times)
    Heater core (backflushed, and later bypasssed)
    Checked for other leaks
    Everything replaced with stock Toyota parts
     
    #1 Jacob Bonner, May 5, 2021
    Last edited: May 5, 2021
  2. mr_guy_mann

    mr_guy_mann Active Member

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    Have never heard about having a cat/ heat exchanger leak before. We are talking about a Gen3 here, so top of the list for causes of overheating is (early stage) head gasket failure. Here are two tests for a mechanic to perform.

    1st test is (on a fully hot engine) to pressure test the cooling system. Here a pump with a gauge on it is attached to the radiator in place of the cap and the system is pressurized to the max allowed (15psi?). Leave the car overnight with the system pressurized. Next day remove the spark plugs and use a videoscope to inspect the cylinders for any coolant.

    2nd test is to remove the spark plugs and radiator cap. Next manually turn the engine crankshaft until cylinder 1 piston is EXACTLY at the top of the compression stroke. Use a compression tester hose (with the check valve removed) to pressurize the cylinder with (150psi) "shop" air. If there are any head gasket seeps then coolant and air will push out of the radiator neck. Turn the engine to bring the next cylinder in the firing order to Top Dead Center and repeat the process.

    Posted via the PriusChat mobile app.
     
  3. StarCaller

    StarCaller Senior Member

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    Gen 3 has no radiator cap /
     
  4. ChapmanF

    ChapmanF Senior Member

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    The degas-bottle system used on Gen 3 means that the cap you see on the degas bottle is the only filler cap in the engine cooling system, and it's the one you remove when doing a leakdown test.
     
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  5. Jacob Bonner

    Jacob Bonner Member

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    I forgot to include that I replaced my 2012 engine with a 2017 engine, with less than 50,000 miles. The old engine blew a headgasket due to overheating. I've been (intermittently) trying to diagnose the cause of the overheating for a year now (while not driving it longer than a few miles at a time, to make sure it doesn't blow this headgasket).

    There's a whole forum post devoted to attempting to diagnose the overheating (I'm ashamed to admit I inadvertently hijacked someone else's post, but they appeared to be through with it :D). To avoid redundancy, I'll post the link to that:
    Need help! Gas engine overheating. Cannot resolve. | Page 9 | PriusChat

    MY thread, specific to my car, is here (but that was from before I swapped my engine, or even realized I needed to):
    Car knocking, changed spark plugs, problem persists | PriusChat

    Why am I creating a new thread, one might ask? I thought the subject of heat exchange bypass deserved it's own thread. I certainly do welcome any thoughts to the insanity. I'm at my wit's end. I've made up my mind that when I get this thing fixed I'm selling it and getting a different car.
     
    #5 Jacob Bonner, May 6, 2021
    Last edited: May 7, 2021
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