Intermittent High Coolant Temp Message

Discussion in 'Gen 2 Prius Care, Maintenance and Troubleshooting' started by edvalencia, Jul 27, 2018.

  1. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    I have a 2008 Prius with 380,000 miles on it (original owner.) Two days ago, my wife took it to work and about 10 minutes after leaving, she said the master warning light (red triangle) turned on for a few seconds, then it turned back off. It did this about three times, then it stayed off. I checked it for trouble codes with my Torque app, and also a Tech stream usb interface I bought on ebay. Neither showed any trouble codes. Yesterday I drove it to my office, which is a 140 mile round trip commute, and had no issues. This morning, 5 minutes after leaving home I saw the MWL turn on, and a red temp gauge was displayed on the screen. As soon as I slowed, it turned off. Since I had my bluetooth OBD2 still connected, I launched my Torque App. I noticed the coolant temp was showing 255F. After stopping, it dropped below 240F and the warning light turned off. This kept repeating as I drove back home.
    The coolant reservoirs for both the radiator and the inverter are full. Is it possible that I just have a bad thermostat? The only other thing I've noticed is that for several months, the air from the heater is not very hot. I plant to check the electric fan, when I get home. Anything else I should be checking?

    Thanks!
     
  2. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    14,633
    7,398
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2010 Prius
    Model:
    V
    You should check your oil level, it might be out of oil.

    You should also check the RADIATOR, when the car is cool. The reservoir level is not a good indicator of Radiator Fluid level.

    You have to remove the front black radiator cover, and you'll see the radiator cap. If you need to add fluid, it just means something is leaking fluid. Example.....radiator cap, water pump, etc
     
  3. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    Didn't know about the reservoir not being a good indicator. I'll check the radiator itself. I already checked the oil. It burns about 1qt per 1500 miles, so I keep a close eye on it.

    Thanks.
     
  4. edthefox5

    edthefox5 Senior Member

    Joined:
    Jul 25, 2007
    9,173
    4,267
    0
    Location:
    Clearwater, Florida
    Vehicle:
    2007 Prius
    Model:
    Two
    Belt fell off water pump or engine ran out of oil and blew the head gasket.
     
  5. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    I took a good look today, and noticed a lot of coolant splashed around the whole front bottom area. I seems like it's coming out of the reservoir vent hose. There is also a little build up of fluid around the water pump vents. What could cause coolant to leak from the vent hose? Bad radiator cap?
    I'm thinking of replacing the water pump, thermostat, belt and radiator cap. Hopefully this will fix it. All the hoses look good.
     
  6. padroo

    padroo Senior Member

    Joined:
    Jan 11, 2008
    2,763
    2,240
    13
    Location:
    Chesterton, Indiana Another third world country.
    Vehicle:
    2016 Prius
    Model:
    Four
    With your high mileage I would do a radiator flush and new coolant while you are replacing all the other stuff.

    The Prius is touchy about trapped air, there are YouTube videos about removing trapped air, I don't know if Gen 3 Prii are as touchy as Gen 2 or not.

    Worst case a blown head gasket.
     
  7. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    The oil looks good, and I don't see any coolant traces around the exhaust gasket, nor bubbles in the reservoir, so I'm hoping it's not the head gasket. I do plan to do a radiator flush.
     
  8. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,172
    6,247
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    I am sure that permanent damage was caused to the engine since you continued to drive the vehicle knowing the engine had overheated. The drop in temp was probably due to to engine coolant leaking and no longer reaching the engine temp sensor. The actual engine temp remained overheated. Normal operating temp is 185 degrees F.

    1. What was the fluid level in the radiator?
    2. Your question about what could cause coolant to come out of the reservoir: how about excessive pressure in the system due to the engine overheating and fluid exiting via the radiator cap. The issue is not necessarily that the radiator cap is bad - rather the issue could be that the pressure in the system exceeded the normal values and the cap allowed fluid to exit as it is supposed to.
    3. Your observation that the cabin heater was not working well for several months prior to this episode is further evidence pointing to air in the engine coolant loop. It would be reasonable to say that the engine was near overheating all of that time.
    4. I suggest that you plan to replace the engine if you wish to keep the car. Or else tow the car to the salvage yard, 380K miles is an extraordinary service life.

    Here is my theory about what happened to your car:

    a. The engine coolant pump developed a leak at the pump bearing. This is very normal after 80K miles of service life.
    b. Eventually, sufficient coolant leaked out so that the cabin heater operation was impaired.
    c. Because air entered the coolant system via the pump bearing as fluid leaked out, the reservoir did not replenish the radiator and the radiator level continued to drop.
    d. You and your wife continued to drive the car and the radiator level continued to drop.
    e. Finally your wife noticed an overheating indication which showed the coolant level was at a seriously low level. IF at that time you had replenished the radiator coolant, noticed the coolant pump was failing and replaced it, you would be good.
    f. Instead you and she ignored the overheating, which led to your current situation.

    Good luck with your decision about what to do with the engine repair.
     
    #8 Patrick Wong, Jul 28, 2018
    Last edited: Jul 28, 2018
    johnjohnchu likes this.
  9. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    14,633
    7,398
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2010 Prius
    Model:
    V
    It's a leaking water pump that's causing the splash. Change the water pump and belt
     
  10. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    Yeah, I just bought a new pump, belt and thermostat. The car only got driven for a very short period of time, at low speed when the MWL came on.
     
    Raytheeagle likes this.
  11. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    OK. I flushed the radiator, replaced the pump, the thermostat and the belt. I drove the car for 2 hours (75 miles) at high speeds and heavy traffic. The car runs fine and the engine temp averaged 186F, with a couple of short spikes at 196F. Aside from checking the oil, and the coolant levels, what else should I be looking for, to make sure I don't have a bad head gasket?
     
  12. JC91006

    JC91006 Senior Member

    Joined:
    Nov 10, 2013
    14,633
    7,398
    0
    Location:
    Los Angeles, CA
    Vehicle:
    2010 Prius
    Model:
    V
    for the next 3 days, every morning, check the radiator coolant level. Fill until full. It takes a few days for all the air to go away.

    You probably don't have a bad head gasket. You may want to change the radiator cap if you haven't done so already
     
    johnjohnchu and edvalencia like this.
  13. edvalencia

    edvalencia Junior Member

    Joined:
    Mar 21, 2008
    20
    1
    0
    Location:
    Lancaster, CA
    Vehicle:
    2008 Prius
    I was planning to change the cap, but they didn't have it in stock. It's on my to-do list. Will check and fill the coolant daily.
    Thanks!
     
  14. Patrick Wong

    Patrick Wong DIY Enthusiast

    Joined:
    Mar 8, 2008
    18,172
    6,247
    0
    Location:
    Green Valley, AZ
    Vehicle:
    2015 Prius
    Model:
    Two
    Looks like you dodged a bullet, kudos to you.
     
Loading...