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changing the raditator-to-heater-core hoses

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by woodpecker, Feb 15, 2001.

  1. woodpecker

    woodpecker Registered Member

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    Mount Vernon, WA
    Hi guys,

    Okay, rookie question alert:

    I'm going to change the heater-core hoses as mine are starting to bulge. I know that i need to let some water out via the petcock on the radiator. From there I have two questions:

    1. What are the hose sizes again? I heard that the top and bottom hoses were actually diff. diameters.

    2. When I go to fill the radiator back up, what is the correct procedure. I've heard of guys running the truck with the rad.cap off allowing air to purge, while filling the radiator up as the level drops and the engine reaches operating temp. I tried this once on a F##d and it seemed like all the coolant just kept coming up and out of the radiator with no appearant air bubbles.

    A quick few sentences on the correct how to regarding radiator re-fill and air purge would be greatly appreciated.

    woodpecker
     
  2. Burt4x4

    Burt4x4 3/4 ton status

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    Location:
    California (Modesto area)
    Well on my 72 the hoses are both the same size and I duno what that size is 5/8 or something??

    This is how I keep my cooling system "air free".
    after hookin everhthing backup I fill the rad with a gallon of coolent then top off the rad with water. I then start the motor with the rad cap off and allow it to warm up. I am waiting for the thermostat to open and pull the fresh coolent mix into the motor. As the rad coolent level drops after the thermo opens I fill to the top with water then cap it off.
    I also use an overflow bucket, catcher whatever you call it for the fliud to overflow into. This is the key to having an air free coolent system. the overflow hose will allow air to 'suck' into the radiator so if that overflow tube is submerged in coolent then is will only suck in coolent and not air.
    Hope this helps!
    Goto my site to see a recient shot of my engine and you will see the overflow bucket.

    72K5[​IMG]Led Zeppelin[​IMG]Rock ON![​IMG]
    <A target="_blank" HREF=http://www.burt4x4.coloradok5.com>http://www.burt4x4.coloradok5.com</A>
     
  3. Rob 85K5

    Rob 85K5 1/2 ton status GMOTM Winner

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    One hose is 3/4" and the other is 5/8". To fill it back up, use half water and half coolant if it is way low, otherwise use water. Fill the puke tank up first, then take your time filling it up the radiator at least til your running the normal operating temp. When the collant stays at the top for a minute or two, put the cap on and your done. The 50/50 mix is what we use here in Florida.


    Rob 85K5

    <font color=orange>Bleedin' Chevy Orange</font color=orange>
     
  4. Corey-88K5

    Corey-88K5 1/2 ton status

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    I just replaced my 88's and they both were 5/8. The computer didn't list the special molded hose in the rear that comes out of the fire wall into the block and cycles around though.

    I have always jsut filled the radiator as the truck was running. Then I drive it a bit, and refill the radiator.

    Hope that helps,

    Corey
    88K5

    Oh, and turn the heater on?.?.? For some reason or another. not that it should matter. it cycles through the heater core regardless. Never the less I always do it.

    [​IMG]<font color=red>Girls Like Guys In Bow Ties
    <A target="_blank" HREF=http://www.geocities.com/corey_perez>http://www.geocities.com/corey_perez</A>
     
  5. HarryH3

    HarryH3 1 ton status Author

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    Corey, you've got it. The "turn the heater on" instructions really only apply to vehicles that have a water valve in one of the heater lines. The valve prevents coolant from flowing through the heater core until heat is called for. Our rigs have coolant flowing through the heater core all the time. An air door determines whether incoming air flows through the core or not.

    <font color=black>HarryH3 - '75 K5</font color=black>
    <A target="_blank" HREF=http://ThunderTruck.ColoradoK5.com>http://ThunderTruck.ColoradoK5.com</A>
     
  6. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    First hit the local Grocery store and get 2 gallons of DISTILLED water...not mineral or spring, DISTILLED water. Tap water, mineral, spring water all have minerals in them and will become acidic over time. this will eat at the cooling system cause it to fail sooner.
    On 73-80 I know the top line that runs to the radiator is 3/4 and the botom line that runs to the intake is 5/8's Somebody said the later models were both 5/8's That may be on trucks that the return line goes to the waterpump. Not sure where that year brake is. I think it may be 87 when it went FI.
    As for filling..if you don't know how old that coolant is you might want to drain the whole system and replace it all.
    On either side of the block right above the oil pan you will find a drain plug that you can get most of the water out of the engine. Draining the radiator will still leave about 1.5 gallons in the block if you don't pull the two plugs. If there is a lot of sediment in the block you will have to take a coat hanger and stick it in the drain holes to brake it up to get it to drain (that's crap from using tap water).
    Might as well toss on some new radiator hoses and be done with it for a few years.

    Diging it in the dirt with my K5's
    Grim-Reaper
    <A target="_blank" HREF=http://grimsk5s.coloradok5.com/>http://grimsk5s.coloradok5.com/</A>
     
  7. ragtop

    ragtop Registered Member

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    My TBI '88 has a 3/4 to the radiator and a 5/8 to the intake. I know the core (both the origional and the replacement, from Advance Auto) had the two different size outlets. I use 50/50 and fill it cold, bring it to 180 deg plus, top off the rad, half fill the overflow tank, cap the rad and then check the overflow tank again after it cools. Seldom have to add any more. I love this thing... it takes me 2+hours to fill my Z-28 since the rad is lower than the engine!

    Ragtop - '88K5 [​IMG]
     

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