Fluctuating Temperature

Discussion in 'Maintenance/Repair' started by OxTheBlueBabe, Mar 11, 2018.

  1. OxTheBlueBabe

    OxTheBlueBabe Newbie

    Joined:
    Feb 16, 2013
    Messages:
    13
    Likes Received:
    0
    Location:
    Tucson, AZ
    Truck:
    1984 2wd Longbed
    A week ago my engine temperature sometimes (not consistently) started creeping all the way up to the red whenever I was at a low RPM. There were no obvious signs my water pump was bad, and based on some reading I did and the gurgling coming from my heater core, I concluded it was probably just air in the cooling system. My overflow tank had run dry, and I've hardly added any coolant since I got the truck five years ago, so I figured it was neglect.

    So yesterday I put the front end on some ramps, slid my heat control all the way to the right (the hottest), and drained the system. When it stopped, I pulled the upper radiator hose and stuck a garden hose in the thermostat housing just to see if it flowed while cold. It did. So I let it flow until the fluid coming from the petcock ran clear, then shut off the water and pulled the thermostat. It wasn't corroded, but what appeared to be a rubber seat on the thermostat mechanism had worn away, and it was no longer seating (hence the cold water flow), so I put in a new one.

    So system flushed and thermostat replaced.

    With everything back together, I filled the radiator, started the engine, and used this DIY method to release the residual air bubbles while the engine warmed up. I raised the RPMs just a bit to speed things up. Within 10-15 minutes I had a hot upper radiator hose and hot air coming out of my vents, and after a while no more air bubbles. I thought I was golden, so I let the RPMs drop to normal idle... and the temp needle immediately started climbing all the way up.

    What gives? I followed all the steps to purge the air, and the hot radiator hose and vent air indicate the water pump is doing its job, right?

    Question: should I be able to *see* the coolant rushing by the radiator opening with the cap off once the thermostat opens? I seem to remember that being the case with my SlantSix engine (though it's been a while), but the coolant looks pretty still in this case.

    Observations? Suggestions?
     
  2. fred heath

    fred heath Enthusiast

    Joined:
    Dec 29, 2011
    Messages:
    251
    Likes Received:
    33
    Location:
    Raleigh, NC
    Truck:
    1978 Toyota Galavan Motorhome.
    It sounds like a bad thermostat. Even new ones can be defective. Is it the correct temp for your engine?
    Once the thermostat opens,you should be able to see the coolant moving with the radiator cap off. You should also feel it moving through the upper radiator hose. What type of engine do you have?
     
  3. jetas

    jetas Grand Toyotaholic

    Joined:
    Mar 26, 2009
    Messages:
    4,674
    Likes Received:
    329
    Location:
    Oxnard, CA
    Truck:
    72.5 Hilux
    Test the temp sensor
     
  4. TRUCK ACTION

    TRUCK ACTION Grand Toyotaholic

    Joined:
    Jan 5, 2008
    Messages:
    3,532
    Likes Received:
    179
    Location:
    Vallejo,Ca.
    Truck:
    88 Extracab,2wd
    If the coolant is going down( low) may be a bad head gasket, if low have a reading taken at the water filler.
    This will let you know !!
     
  5. OxTheBlueBabe

    OxTheBlueBabe Newbie

    Joined:
    Feb 16, 2013
    Messages:
    13
    Likes Received:
    0
    Location:
    Tucson, AZ
    Truck:
    1984 2wd Longbed
    Thanks to each of you for your reply.

    Fred, I verified the thermostat is the correct temperature for my engine, which is a 22R. The previous thermostat was stuck open and the symptoms are the same before and after. And again, the water seems to be entering the heater core, so I'm reluctant to think the thermostat was/is the issue. I'll check again for signs of flow in the radiator in the morning.

    Jetas, I should ask: where does the engine temperature needle sit on the gauge for most warm 22R engines? Before this started up last week, I don't think I'd ever seen mine move. It doesn't indicate a "Normal" range, so I assumed this was intentional. I'll look in to testing it - it appears my manual gives a few suggestions. Have you ever seen one go bad in this manner?

    Truck Action, I don't *believe* this is the case, but I will certainly check again for more signs. I'm not sure what you mean by having "a reading taken at the water filler." Care to clarify?

    Thanks again, guys.
     
  6. OxTheBlueBabe

    OxTheBlueBabe Newbie

    Joined:
    Feb 16, 2013
    Messages:
    13
    Likes Received:
    0
    Location:
    Tucson, AZ
    Truck:
    1984 2wd Longbed
    Truck Action, do you mean the color changing liquid? I think I saw something about that before.
     
  7. Hands_On_Henry

    Hands_On_Henry Member

    Joined:
    Dec 5, 2017
    Messages:
    82
    Likes Received:
    16
    Location:
    Michigan
    Truck:
    1985 22R/4spd
    Good input already here. I would just add that IF you're burning coolant your spark plugs will tell you.
     
  8. OxTheBlueBabe

    OxTheBlueBabe Newbie

    Joined:
    Feb 16, 2013
    Messages:
    13
    Likes Received:
    0
    Location:
    Tucson, AZ
    Truck:
    1984 2wd Longbed
    All is well. Not a blown head gasket or even a bad water pump. Didn't know there was a sensor AND a sending unit. See post #3 here. Wire to the sender was disconnected, and probably has been for the five years I've owned it (mine is black, for some reason, making it all the more difficult to spot). Reconnected it and all is well. The needle actually rises to about 1/4 of the way up once it's warm, now, and stays there.

    Still a mystery as to why it suddenly started acting all haywire, but only $40 later I have fresh coolant, a functioning thermostat, and now a functioning temperature gauge - so this was all for the best. Thanks for the input, guys.
     
  9. Hands_On_Henry

    Hands_On_Henry Member

    Joined:
    Dec 5, 2017
    Messages:
    82
    Likes Received:
    16
    Location:
    Michigan
    Truck:
    1985 22R/4spd

Share This Page