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water temperature sensor ?

Discussion in 'Chevy Trucks' started by blzn74, Jan 27, 2002.

  1. blzn74

    blzn74 Member
    Messages: 45

    Does anyone know if the water temperature sensor ever fails? Not the thermastat, but the actual sensor that screws into the side of the block ,driver side exaust manafold area, that sends the signal to the gauge in the dash. If so what are the symptoms.? The problem Im having is the gauge reads about 195 untill I hit the freeway and then skyrockets to 250, while it read 250 I had a shop check the actual temp, and it was only 200, I checked for a bad ground and couldnt find it,so im trying to elimiate possible causes.
     
  2. reallyrusty

    reallyrusty Member
    Messages: 71

    Yes they do fail. make sure your coolant level if full and that your not measuring a steam pocket. The sender is a variable resistor to ground. When it fails towards no resitance the guage goes full scale. If it fails to infinite resistance the gauge won't register. I've see both failures.
    hope this helps
     
  3. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    Yes,they definetely do fail,my 91 GMC did the same thing,it was reading real high,I put a new one in,and all problems solved.
     
  4. blzn74

    blzn74 Member
    Messages: 45

    Thanks for the info guys, I dug around some more under the hood, and noticed my sending unit for the oil pressure is missing , yet my gauge in the cab is always pegged, and when I turn the accesory on the oil needle mooves. If there is no sending unit or wire going to the instument cluster, How the heck is it reading a signal, Possible short?, Possible miss wireing?, I'll tear the dash apart and see whats hooked up to the oil gauge. That could be my whole problem. Ill let you guys know what I find.
     
  5. reallyrusty

    reallyrusty Member
    Messages: 71

    i'm going to ASSume (Which i shouldn't) that we're talking about an older c/k. The oil gauges were mechanical and controled by a pressure tube and not an electric sender. I don't know what year they went electric but my 74 has a tube.
    hope this helps
     
  6. John DiMartino

    John DiMartino PlowSite.com Veteran
    Messages: 2,154

    My 77 Suburban had a tube,my 81 Suburban had an electric guage, somewhere in between there they changed over.
     
  7. blzn74

    blzn74 Member
    Messages: 45

    Bad wiring.....

    Ok, this is whats going on, the truck is an 81 chevy 4x4 3/4ton with a new small block in it, it looks like the owner before me put the wiring together half ass, after further checking into the wire job, I found that the oil pump pressure sending unit, (on top of the block in the rear,under the distributer cap,) was not installed, just pluged closed, thus the wire to the gauge in the cab was not grounded, just hanging, the reason seams to be because the stock Manifold intake was removed and replaced with an Eldebrock Performer series intake, thus the stock oil pump sending unit would not fit without a little altercation. I made the altercation to fit the sending onto the block and IT WORKS! The Oil gauge is no longer pegged at all times, fired it up and it went to 60. I fixed it on my lunch break at work but I havent had time to let the truck warm up to check the rest of the gauges, could that of been the bad ground I was looking for? I will post an update when I find out.
     
  8. RTallday

    RTallday Member
    Messages: 79

    ok, first of all, your temperature sender. Its probably bad, cause i had the same thing happen to me. Just to test that its not the gauge, take the connection off the sender and touch the metal inside the plug to ground, and the gauge should get pinned. If it does, the gauge is good, its the sender. They are easy to change, but dont put too much silicone on the threads, u dont wanna block the sender from grounding itself. Also, your oil pressure gauge, if you have an older one with the tube and stuff, thats a pain. I THINK you have the electric gauge cause u said its pinned. Again, the same way the temp sensor works. The sending unit for the oil is on the back of the block on the passenger side. Its kinda large and u cant miss it. If the gauge is ok, then swap sensors. Good luck.

    -Rich