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What vaccuum hoses come from the top of the Thermostat?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by MilpitasK5, Oct 8, 2003.

  1. MilpitasK5

    MilpitasK5 1/2 ton status

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    My 86'(5.7L 350) K5 has two hoses comeing from the top of the thermostat. They appear to be vacuum hoses. One of them goes out toward the passger side and stops right above the exhaust manifold. What is it and what does it do? Where should it actually go. It's just capped off.

    TIA /forums/images/graemlins/ears.gif
     
  2. Confedneck

    Confedneck 3/4 ton status

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    never seen any vacuum hoses from a thermostat..do they actually come from the t-stat housing?? or just near it?
     
  3. Shaggy

    Shaggy 3/4 ton status

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    On mine, the top one goes to the EGR and bottom one goes to the carb for full vacuum.
     
  4. MilpitasK5

    MilpitasK5 1/2 ton status

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    [ QUOTE ]
    On mine, the top one goes to the EGR and bottom one goes to the carb for full vacuum.

    [/ QUOTE ]
    I think Shaggy has the idea, Confedneck.

    Okay... I wonder if the one that's not hooked up does anything. It's capped off for some reason.

    BTW - I'll try and come by tomorrow with some boxes dude! /forums/images/graemlins/thumb.gif
     
  5. 4X4HIGH

    4X4HIGH 1 ton status Premium Member GMOTM Winner

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    Those vacuum lines go to a thermal vacuum switch. what the switch does is only allows vacuum to reach one or more of the ports after the engine warms up to a certain temperature.
     
  6. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I have those lines coming from the stat too, but I disconnected them when I swapped in my 406, I disconnected most of those kind of lines but can't remember where they go, so I am going to have fun with that for smog. /forums/images/graemlins/crazy.gif I still don't understand what the switch is for and why vaccum needs to go to the stat housing.
     
  7. Shaggy

    Shaggy 3/4 ton status

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    Vaccuum isn't going to the stat housing, the stat housing is providing the thermal input for the thermal switch.
     
  8. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    but.....what is the thermal switch for, what purpose does it serve?
     
  9. Shaggy

    Shaggy 3/4 ton status

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    It sends the vaccuum through the switch only when the engine is cold or hot, I'm not sure which in this case since I'm not positive what Chris's is supposed to go to.
     
  10. rjfguitar

    rjfguitar 3/4 ton status GMOTM Winner

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    I relize that, I just want to know what the switch is for, what does it do? what does it control/contribute to?
     
  11. dyeager535

    dyeager535 1 ton status Premium Member

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    It depends on application.

    The switch can be used to change the primary fuel delivery on the carb. It can delay lockup of the torque converter. It can probably be used to reduce vacuum advance. Anything that might need to be controlled only during cold or hot engine operation could use this switch.

    You'll see many different thermostat housing for jsust that reason. Based on year, engine, destination, etc., the vacuum lines running to that switch may have increased or decreased.
     
  12. imiceman44

    imiceman44 1 ton status

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    [ QUOTE ]
    It depends on application.

    The switch can be used to change the primary fuel delivery on the carb. It can delay lockup of the torque converter. It can probably be used to reduce vacuum advance. Anything that might need to be controlled only during cold or hot engine operation could use this switch.

    You'll see many different thermostat housing for jsust that reason. Based on year, engine, destination, etc., the vacuum lines running to that switch may have increased or decreased.

    [/ QUOTE ]

    Dorian has the right explanation.
    Now in Chris's case if it's just 2 hoses that means one comes from the source, and the second should go to the vacuum advance on the dist.
    It only is supposed to advance when the engine is hot.
    When cold it doesn't do anything.
    /forums/images/graemlins/thumb.gif

    Sometimes you will see it with 3 or 4, that means 2 or 3 functions, usually the second would be the tranny shifting points and the 3rd I have seen go to the AIR (smog pump) valves to control air pumping into the exhaust.

    Chris, check to make sure you have a hose connected to your distributor, if you do, then someone bypassed the switch and went with full vacuum on your dist.
     
  13. MilpitasK5

    MilpitasK5 1/2 ton status

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    [ QUOTE ]
    [ QUOTE ]
    It depends on application.

    The switch can be used to change the primary fuel delivery on the carb. It can delay lockup of the torque converter. It can probably be used to reduce vacuum advance. Anything that might need to be controlled only during cold or hot engine operation could use this switch.

    You'll see many different thermostat housing for jsust that reason. Based on year, engine, destination, etc., the vacuum lines running to that switch may have increased or decreased.

    [/ QUOTE ]

    Dorian has the right explanation.
    Now in Chris's case if it's just 2 hoses that means one comes from the source, and the second should go to the vacuum advance on the dist.
    It only is supposed to advance when the engine is hot.
    When cold it doesn't do anything.
    /forums/images/graemlins/thumb.gif

    Sometimes you will see it with 3 or 4, that means 2 or 3 functions, usually the second would be the tranny shifting points and the 3rd I have seen go to the AIR (smog pump) valves to control air pumping into the exhaust.

    Chris, check to make sure you have a hose connected to your distributor, if you do, then someone bypassed the switch and went with full vacuum on your dist.


    [/ QUOTE ]
    The top vacuum hose is capped off. It looks like it could have been going toward that direction. The hose goes to the passger side of the engine and just sits there. Now, I have another post looking for my vacuum advance /forums/images/graemlins/confused.gif. LOL /forums/images/graemlins/crazy.gif
     
  14. imiceman44

    imiceman44 1 ton status

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    See? you found it.
    Your vacuum advance hose sometimes get loose and falls off and this is where it will land, on the passenger side.
    It could have been knocked off when you were adjusting the advance.
    /forums/images/graemlins/thumb.gif
     
  15. MilpitasK5

    MilpitasK5 1/2 ton status

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    [ QUOTE ]
    See? you found it.
    Your vacuum advance hose sometimes get loose and falls off and this is where it will land, on the passenger side.
    It could have been knocked off when you were adjusting the advance.
    /forums/images/graemlins/thumb.gif

    [/ QUOTE ]

    Someone intentionally disconnected it. It has a cap on it.
     
  16. imiceman44

    imiceman44 1 ton status

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    Read my post on the other thread
    /forums/images/graemlins/thumb.gif
     

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