Heating Systems & Thermostats

bstoutbstout Member Posts: 38
edited March 2014 in Toyota
I have a 2000 Toyota Tacoma with no heat all of the sudden. I checked the valve on the firewall and it is working okay. Could this be a thermostat problem? I see a "Heater Relay" in the fuse box under the hood, what function does this perform? The fan is working fine just no heat.


  • andre1969andre1969 Member Posts: 25,455
    If the thermostat fails in the closed position, your engine will overheat. If it fails open, it'll just take longer to warm up in the mornings and run cooler, but you should still get some heat. A heater core is something that usually lasts for years though, so I'm guessing there's some minor little switch, fuse, or valve somewhere that failed.
  • Mr_ShiftrightMr_Shiftright Member Posts: 64,481
    Check your coolant level asap! you could have a leak and without enough coolant there will be no heat.

    Other than that, a likely culprit would be the heater valve, that shuts the hot coolant off and on, into the heater core.
  • wtd44wtd44 Member Posts: 1,208
    A knowledgeable person at NAPA told me the other day that the old heater core valve is essentially history now. The "new way" is to circulate coolant through the core at all times that coolant is circulating. Heat is regulated by "doors" that open and shut in the air stream through the core. He speculated that this evolution has taken place because of the corrosion in cores that used to occur as a result of stagnating coolant standing in them most of the time. Another reason could be the problematic in-hose/in-line valves that fail from time to time.
  • 0patience0patience Member Posts: 1,712
    It is usually found on systems with AC. It regulates how much of the AC you are getting to cool or warm the air.
    If a pen or pencil or something falls down the defrost vents, it can cause the door to not shut all the way and you get no heat.
    If it is vacuum operated door, Then check the vacuum hoses, but I think your's is electronically controlled, so there may be a module up by the heater. The heater relay is for the fan control.

    Have you confirmed that the heater hoses are getting warm?
    What does the temp guage say?
    Is there coolant in the radiator? Have you checked and filled it?
    If everything checks out, then you may have a thermostat stuck open.
  • bstoutbstout Member Posts: 38
    Thank you for the input. I have checked the obvious such as coolant and valve to the heater core. I previously had problems with mice building nests in my air cleaner compartment and they chewed a hole in my air cleaner causing the check engine light to come on. I have since put a piece of window screen in to keep them out. I may have another rodent nest problem. Don't keep your wild bird feed in the garage!
  • wtd44wtd44 Member Posts: 1,208
    I couldn't resist... (:^>
  • jgmilbergjgmilberg Member Posts: 872
    If you have a rodent problem maybe they have chewed through a vacuum line that moves the blend door into the heat position. In my old Chevy van a broken line caused the same thing. The door stays in the last position until vacuum is applies to the other side of the actuator, pulling the door into the heat position. If all else fails try moving the door actuator by hand. Be careful though, forcing it may break something that is really expensive to repair. Not to be a wise guy, but isn't your truck under warranty?!!

    If you keep wild bird seed in the garage try putting it into a steel trash can so the mice/rats can't get to it. Then after awhile they will move to the neighbors house.
  • wtd44wtd44 Member Posts: 1,208
    Once when living in a wooded area, I learned the hard way to not leave used motor oil in gallon plastic milk jugs out in the remote garage. A rat of some type gnawed through a jug, but failed to consume the black oil that he liberated! What a mess.
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