Need help! Gas engine overheating. Cannot resolve.

Discussion in 'Gen 3 Prius Care, Maintenance & Troubleshooting' started by Sergey K, Apr 1, 2019.

  1. Sergey K

    Sergey K Junior Member

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    I was recently driving down the highway and saw the engine overtemp light come on on my dash. I pulled over and looked under the hood and the coolant was boiling in the reservoir. Bad sign. Coolant was slightly below the low line from evaporating and boiling coolant coming out of the reservoir cap.


    I have a 2011 Toyota Prius Level 5 with 77,000 miles with no modifications of any kind.

    PROBLEM: Engine coolant overheats up to 235F while driving at high speeds (65mph) under heavy load (going slightly uphill on highway at high RPMs). At low speeds under 60mph or when the car is idle, no overheating occurs.


    REPAIRS TRIED:

    1. Replaced coolant reservoir cap:
    I started with the most inexpensive part to replaced: the reservoir cap. I got a replacement from Toyota dealer. If the cap is not holding the correct pressure in the reservoir, the coolant can boil faster than necessary. I replaced the cap and filled up the reservoir to the max line. Replacing this made no effect, I had the same overheating problem.

    2. Replaced thermostat: Got a new thermostat from Toyota and replaced it. When draining the coolant, it all came out clean, debris free. Checked the old thermostat in boiling water and old one still worked as well. Installed the new thermostat regardless. Replacing this made no effect, I had the same overheating problem.

    3. "Bled" the cooling system: Spent about a couple hours running the car up to temp and squeezing all of the coolant hoses. Had the heater on high with lowest fan speed. Doing this made no effect, I had the same overheating problem.

    4. Checked the coolant temp sensor: Removed the coolant temp sensor and tested with an ohm meter according to the Prius service manual. Sensor is working as normal. No issues found.


    5. Replaced the radiator: Some friends kept telling me the radiator is probably partially clogged and is likely the issue. Ordered a new radiator and installed it. Again, old coolant came out clean, debris free. Filled new coolant into new radiator and bled the system again. Replacing this made no effect, I had the same overheating problem.


    6. Replaced the water pump: I left the costliest part for last. But my Prius started showing me 1 engine code: P148F: Engine coolant pump over revolution. I'm not sure if this code was here the whole time or not and I'm not sure what it really means. I bought a brand new water pump and installed it, filled system with new coolant, and bled the system. The engine code went away and I'm not seeing it at this time. Replacing the water pump made no effect, I still have the same overheating problem under heavy load at high speeds.


    I checked the service manual and the 3rd gen Prius normal operating temp is 176 to 212F. Mine spikes up to 235F (and would prob go higher if I didn't pull over right away).


    Some more notes:
    1. I dont think it's a blown head gasket because the coolant does not leave the system except when it boiled over. It stays put at the max line now that I pull over before it boils and the oil is clean and not getting mixed with coolant.
    2. Both radiator cooling fans work and blow the correct way.
    3. The cabin heater works fine and blows very hot air within several minutes.
    4. I'm also using the Toyota brand pre-diluted 50/50 pink coolant. Never used anything besides Toyota coolant.
    5. No other engine codes or issues come up.
    6. When the car is heated up (over 165 or more), the coolant is going around as the left thick coolant hose stays cool and the right thick coolant hose gets fairly warm.


    HELP! I've spent so much money and time and literally replaced and/or tested everything I can!!! I need this car for work. I don't know what else to test. It only overheats under load at freeway speeds. If I drive 60mph or less on flat roads, I see no overheating issues and the coolant always stays under 200F.

    Am I missing something? Could I still have an air bubble somewhere in my hoses? What can I do???
     
    2012 Prius v wagon 3 likes this.
  2. Patrick Wong

    Patrick Wong DIY Enthusiast

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    Has the car been in a front end accident? If yes,check what direction the radiator fans are blowing air. The fans should be sucking air from the outside, towards the engine. If the opposite, that would explain overheating at higher speed.
     
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  3. The Critic

    The Critic Resident Critic

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    Are both hoses going into and out of the heater core, hot?

    The fact that one rad hose is cool and the other is hot leads me to believe that you still have an issue with flow.

    If you allow the engine to idle in maintenance mode, does it still overheat?
     
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  4. Sergey K

    Sergey K Junior Member

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    Verified that both radiator fans are blowing correctly. They suck air from the front of the car and blow air into the engine.

    The radiator hoses are warm/cool when it sits idle. I have yet to test it when the car overheats.

    No, the car will not overheat in maintenance mode. It doesnt even overheat when driving for 30+ mins under 60mph. It only overheats going up hill on the highway at 65mph+. It happens when the car is under heavy load and at very high RPMs.

    How can I be sure the coolant system has no air bubbles?

    Any other ideas of what it can be?
     
    #4 Sergey K, Apr 1, 2019
    Last edited: Apr 1, 2019
  5. Mendel Leisk

    Mendel Leisk Sand Pounder

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  6. Sergey K

    Sergey K Junior Member

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    Mendel, I saw that post. Nothing conclusive there. I did a ton of googling and found that that code is only fixed by replacing the water pump.

    I replaced my water pump and the code has gone away. I dont get that code anymore, but I do still get the overheating under heavy load at high speeds.
     
    #6 Sergey K, Apr 1, 2019
    Last edited: Apr 1, 2019
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  7. tankyuong

    tankyuong Senior Member

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    There’s still air in the system which explains the over revving
     
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  8. Patrick Wong

    Patrick Wong DIY Enthusiast

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    How long have you owned this 2011 Prius?
    Is the overheating problem a recent occurrence?
    Did anything happen to the car prior to the start of the overheating, which might be related to that problem?
    What mpg is the car logging, and has that changed over the course of your ownership?

    I assume that you are driving with the gear selector in D (not B.)

    When the engine starts to overheat, I understand that you pull off the highway. Then what - do you open the hood to inspect?
    Is the engine still running?
    Are the radiator fans running really fast; or not so fast?

    There are three radiator fan relays and two associated fuses: 40A RDI and 30A CDS.

    The engine ECM can switch between a slow fan speed (where the two fan motors are connected in series) and a fast fan speed (where the two fan motors are connected in parallel).

    There are two radiator fan motors. When applying 12V to the fans, one is supposed to draw 4.7 to 8.7A current, while the other is supposed to draw 7.4 - 11.4A current, hence the second fan should spin faster since it consumes more power.

    One test might be to disconnect the radiator fan motor wiring harness connectors, then apply 12VDC directly to each fan. Observe how fast they spin and what noise they make. Then reconnect the fan wiring harness connectors, drive the car, get the engine almost to the point of overheating, then see how fast the fans are spinning and their noise level.
     
    #8 Patrick Wong, Apr 1, 2019
    Last edited: Apr 2, 2019
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  9. Sergey K

    Sergey K Junior Member

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    Patrick,

    -I've owned this car since 2013.
    -Yes, its a new occurence. It has never overheated in the past.
    -Nothing has happened that may have triggered this that I can think of.
    -Its showing 40 to 42 MPG on average which is what it always has got in the past.
    - Yes, Im driving in D gear selector.
    -When it overheats, I pull over and put the car in park. I open the hood, the engine still runs. The radiator fans are running as well. I wait for it to cool back down and then start driving again. I never paid attention to the speed of the fans. I know they run but I wouldnt know how to tell if its fast or slow.

    Tomorrow, I will try the 12V test to each fan and try to compare the fan speeds to an overheating situation as you suggested.

    I'll also compare the hose in/out temperatures from the radiator after it overheats.

    Im still not sure if there is air pockets / bubbles in the hoses and I dont know how to tell if there is. I have been replacing parts almost every other day and I have a feeling there is air somewhere which isn't letting the coolant circulate properly.

    The way I bled the system is:
    -Filled reservoir with coolant slowly until the B line.
    -Once it held the line, with the reservoir cap still open, I started the car in maintenance mode with heater temp high and heater fan low.
    -I squeezed all the coolant hoses by hand one at a time.
    -Filled the reservoir again and put the cap on.
    -Drove the car on the highway to get over 185F so the thermostat opens.
    -Came home, parked, and filled the reservoir again.
    -Squeezed all the hoses again by hand.
    -Made sure the coolant is at the F level.

    Should I be doing something different to bleed the system?

    I'll post a reply about the fan test tomorrow.
     
    #9 Sergey K, Apr 2, 2019
    Last edited: Apr 2, 2019
  10. Sergey K

    Sergey K Junior Member

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    Another thing I noticed is the new water pump housing gets really, really hot when the pump is running, even when car is idle. The old water pump got just as hot. Its so hot that its almost too hot to touch. Is that normal? Maybe no water is getting to it?
     
    #10 Sergey K, Apr 2, 2019
    Last edited: Apr 2, 2019
  11. Dxta

    Dxta Senior Member

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    That cooling system still has some air pockets in it.
     
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  12. tankyuong

    tankyuong Senior Member

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    Try loosening the bleeder valve
     
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  13. jerrymildred

    jerrymildred Senior Member

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    +1 to @tankyuong. I'm pretty sure the '12 has a bleeder valve.

    Also, I wonder if there's a possible malfunction in the valve or gate or whatever it's called that routes coolant to the catalytic converter to warm the engine. If that's stuck in "warm-up" position, the coolant would get really hot and under high engine loads, it would get even hotter as the cat heats up.

    Also, re: the hose temperatures. One would expect the hose from the rad to be not as hot as the one from the engine to the rad. If they were the same, then the radiator isn't exchanging the heat as it should.
     
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  14. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I'm pretty sure the 12's don't have a bleeder valve. You're talking about the valve on the coolant hose above the EGR? What you could do though, is just disconnect one of the small hose ends, the hose atop the EGR. A little awkward, but should accomplish the same thing.

    I wonder WHY they eliminated the bleeder valve??Other cars, as I fill the coolant with bleeder valve open, you can feel a strong air gush as you pour the coolant in. Why the heck would you NOT want that?
     
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  15. sam spade 2

    sam spade 2 Senior Member

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    Sure sounds like there is a flow problem here somewhere.....either air flow or water flow.

    Any chance that the GRILL is blocked by something ?
    Or that the water pump belt is slipping ?

    By now, you probably have spent FAR more time and money than a professional shop would have charged you.
    Maybe it's time to give up and take it in.
     
  16. mjoo

    mjoo Senior Member

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    With heavy load the ECU will drive the engine VVT to give it timings closer to an otto-cycle than an atkinson-cycle for extra power. That alone should increase engine temperatures.

    Have you considered the EGR system? What's the condition? My EGR system was near plugged around 69k miles. The job of EGR is to bring peak engine combustion temperatures down by several hundred degrees fahrenheit and also peak combustion pressures.
     
  17. jerrymildred

    jerrymildred Senior Member

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    No. On the back side of the top left of the radiator. Now that I think of it, I'm remembering my wife's '07. Did all the Gen 3's lose it? I don't remember looking for it on my '13 PiP.
     
  18. Mendel Leisk

    Mendel Leisk Sand Pounder

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    I'm pretty sure third gen engine coolant bleed bolt was nixed in model year 2012. Prior to that, it's a T-junction sort of contraption, with a white cap, on one of the hoses above EGR cooler. It's way back there, kinda hard to see or access, till the wipers and cowl are off.

    upload_2019-4-2_9-53-37.png
     
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  19. Sergey K

    Sergey K Junior Member

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    Sam Spade: The 3rd gens dont have any belts at all. By grill, if you mean the radiator, no its not blocked or clogged and I replaced it. Its brand new and nothing is blocking it.

    Mjoo: If it'd be a dirty EGR, wouldn't I see a performance issue and or MPG drop? I'm not seeing that.

    TankYoung / Jerry Mildred: the 3rd gen 2011 and up got rid of the bleeder valve. I spent a few hours looking for one. There is not one anywhere. Not on radiator nor the T contraption by the coolant sensor.

    Mendel Leisk: Pulling a small hose from the top maybe a good idea. I may try that. Im just worried it will gush coolant everywhere.

    I will check the fan speeds and coolant hose temps when it overheats today.

    Any other ideas in the meantime? Id love to hear anything.
     
    #19 Sergey K, Apr 2, 2019
    Last edited: Apr 2, 2019
  20. Mendel Leisk

    Mendel Leisk Sand Pounder

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    Yeah just get it loose and gently lift it off, being prepare to push back on quickly if needed. If there's air at the top there shouldn't be a gush. That was the bleed bolt loc, for 2010/2011.

    The fill sequence (screen grab from attachment up the page):

    upload_2019-4-2_10-39-41.png
     
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