1. Attachments are working again! Check out this thread for more details and to report any other bugs.

Bypassing Heat Exchanger

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

  1. Jacob Bonner

    Jacob Bonner Member

    Joined:
    Feb 7, 2019
    86
    44
    1
    Location:
    United States
    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 Senior Member

    Joined:
    Sep 3, 2020
    3,676
    1,718
    0
    Location:
    NJ-USA
    Vehicle:
    2006 Prius
    Model:
    Four
    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

    Joined:
    Feb 15, 2014
    1,257
    706
    0
    Location:
    Cedar Crest, NM, USA
    Vehicle:
    2014 Prius
    Model:
    Two
    Gen 3 has no radiator cap /
     
  4. ChapmanF

    ChapmanF Senior Member

    Joined:
    Mar 30, 2008
    24,915
    16,216
    0
    Location:
    Indiana, USA
    Vehicle:
    2010 Prius
    Model:
    IV
    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.
     
    StarCaller likes this.
  5. Jacob Bonner

    Jacob Bonner Member

    Joined:
    Feb 7, 2019
    86
    44
    1
    Location:
    United States
    Vehicle:
    2012 Prius
    Model:
    Two
    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
  6. AmazingFacts

    AmazingFacts Member

    Joined:
    Aug 6, 2021
    112
    61
    0
    Location:
    San Jose
    Vehicle:
    2016 Prius
    Model:
    Two Eco
    Jacob, did you ever figure out the overheating issue? Maybe there's some large calcium coolant deposits stuck in the coolant system. Have you tried flushing via the large upper/lower coolant hoses with a garden hose?
     
  7. Ivan Barrios

    Ivan Barrios Junior Member

    Joined:
    Jul 20, 2020
    4
    0
    0
    Location:
    Kissimmee Florida
    Vehicle:
    2005 Prius
    Model:
    Four
    I saw you mentioned in your post that you once bypassed the heater core on your gen 3 Prius can you tell me how how to pass it i have Gen 3 with a heater core problem, and want to do bypass it if you have picks that would help also

    If you have pictures or a video of the heater core problem that would help also thanks
     
    #7 Ivan Barrios, Jun 19, 2024
    Last edited by a moderator: Jun 19, 2024
  8. Marcilla Smith

    Marcilla Smith Active Member

    Joined:
    May 14, 2018
    123
    117
    3
    Location:
    Raleigh, NC
    Vehicle:
    2011 Prius
    Model:
    N/A
    :: bump ::

    I see people talking about a bypass for the Gen 3 exhaust-coolant heat exchanger, but not the how. I could really use that information, please!
     
  9. bisco

    bisco cookie crumbler

    Joined:
    May 11, 2005
    110,166
    50,060
    0
    Location:
    boston
    Vehicle:
    2012 Prius Plug-in
    Model:
    Plug-in Base
    i don't recall it ever being done, but maybe i missed it
     
  10. Mendel Leisk

    Mendel Leisk EGR Fanatic

    Joined:
    Oct 17, 2010
    56,693
    39,238
    80
    Location:
    Greater Vancouver, British Columbia, Canada
    Vehicle:
    2010 Prius
    Model:
    Touring
    OP started a new thread, on same car, same saga, and forgot a "minor" detail.
    What's the miles on it? Original water pump? EGR ever cleaned?
     
  11. Marcilla Smith

    Marcilla Smith Active Member

    Joined:
    May 14, 2018
    123
    117
    3
    Location:
    Raleigh, NC
    Vehicle:
    2011 Prius
    Model:
    N/A
    Ok, so I decided against waiting and went ahead and did it. To the next person who finds this thread, I apologize that I didn't video record the effort for you, but FWIW, here's some kind of write up for you:

    The lower hose is relatively easy to see once you raise the driver side. I started by clamping off the lower hose with some $5 straight nose locking pliers. But what YOU are going to want to do is remember to go ahead and use that second set of those $5 pliers to pinch off the upper house as well, before proceeding.

    Believe me when I tell you that upper house is there, but it's tucked up in there, I'm sorry to have to tell you. Make sure - REALLY sure - that everything down there is cooled off before you stick your hand up in there (just like you were sure to chock the wheels and use a jack stand!).

    Ok, now that you pinched off both of your hoses - leaving plenty of room to back the hose clamps off - you can pinch that bottom hose clamp with your pliers and slide it back into the hose, past the point where it's covering the pipe.

    Now take your channel lock pliers - it if you're fancy enough to have hose pliers - grip the hose where it covers the pipe, and twist it back and forth to break it free from the hose. Then, you can grab it further back with your hand, and wiggle it free.

    Now, even if you remembered to pinch off both hoses and did a good job of it, a little coolant is still finna come out at this point, so be prepared.

    Next, your gonna wanna have a 3/4" brass 90° barb from the PEX section of the Lowe's where you're doing your shade tree mechanicing in their back parking lot. Go ahead and stick one of the barbs all the way in the lower hose, then pinch that hose clamp spring and slide it back on. Make sure the free end of the 90° bend is pointing up.

    Alright, now if you have one of the aforementioned fancy hose pliers, you might could get it up in the little space good enough to wiggle that upper hose free. If you're like me and just working with some channel locks and long nose pliers, well then you're gonna be lucky just to get enough space to get that hose clamp spring backed off. You sure ain't getting that hose broken free of the pipe and wiggled off - save yourself the effort!

    So what I did - IDK that I recommend this part, but I include it for the sake of thoroughness - is that I took my tin snips/aviation shears and just cut it off.

    Now, be aware that this is going to cause more coolant to drain from the heat exchanger.

    Now it's just a matter of placing the other barb end in the upper hose, sliding the corresponding hose clamp to secure, removing the locking pliers, securing the hoses (I zip tied the brass elbow to the upper pipe), and adding coolant back to the reservoir.

    If you're reading this, I hope it helps!