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Cooling problem

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by '73 K5, Sep 12, 2001.

  1. '73 K5

    '73 K5 1/2 ton status

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    I've been having an ongoing problem in this area, so I thought I'd see what you guys think.
    When my truck has sat overnight and I take it out to drive the temp. will slowly climb to about 180 or 190...then when it reaches that point, it sky rockets to around 230 degrees in just 5-10 seconds....then as quickly as it gets to 230, it drops back down to 190 or so very quickly. Then the whole rest of the time I drive the truck it will stay around 190. It does the "230 thing" in 100 degree weather just the same as it does it in 60 degree weather.
    My old gauge did this, as does my new Autometer gauge. I've also gone through 3 thermostats (195 degree) and they all have done the same thing. Both hoses are new. The radiator, water pump and heater core are all only 2 or 3 years old with very low miles. I also flushed the radiator with that Prestone stuff and that didn't change anything either.
    Could it be the position of the temp. sensor in the intake??? I have Vortec heads which use the different intake.
    Any other ideas?

    '73 K5
    Chevy good...Ford bad
     
  2. Neil

    Neil 1/2 ton status

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    try a different temp.sensor. if not that maybe try a 160 thermostat to see what that does. sounds like a temp sensor or connection to gauge.

    Neil H. Alabama.. "It's a full size thang, Jeep owners don't understand!!" '78 K5 400ci 4x4 AT,AC,PW Cheyenne., '74 C10 4x2
     
  3. hawglet

    hawglet 1/2 ton status

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    Did you replace the sensor when you put in the new gauge? If not that would be where I would start, If so I have no other GUESSES!!!



    Thanks,
    Greg Gayman
    Hawglet
    Stovie
    hawglet@excite.com
     
  4. DesertDueler

    DesertDueler 1/2 ton status

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    I have my temp sensor in the head and it climbs to 220, then drops back to 195. Thats with an autometer gauge. It is ok for it to reach that temp as long as it doesnt stay there. for a long time.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  5. '73 K5

    '73 K5 1/2 ton status

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    They were both mechanical gauges...no sensor to mess with. So the whole deal was switched out when I went to the new gauge.

    '73 K5
    Chevy good...Ford bad
     
  6. DesertDueler

    DesertDueler 1/2 ton status

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    Mines a mech gauge too.

    86 Jimmy 4"lift 35"MTRs Other cars 69Firebird w/525 hp,and 70GTO live in PHX,AZ<a target="_blank" href=http://www.geocities.com/modifierperformance>My vehicles</a>
     
  7. '73 K5

    '73 K5 1/2 ton status

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    Hmmm. Maybe thats just a weird characteristic of those mech. gauges. I'm sure its not hurting the engine, because it doesn't do it but just for a few seconds, but it didn't always do this...just kinda strange I guess.

    '73 K5
    Chevy good...Ford bad
     
  8. txguy

    txguy 1/2 ton status

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    I have a Supra, the blow by on the power stroke pushes hot air into the circulating water and has caused this...
     
  9. BigTex

    BigTex 1/2 ton status

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    What's better, electric or mechanical gauges?

    <font color=red>"Maybe you could drive better with that cell phone up your azz?!!!"</font color=red>
     
  10. '73 K5

    '73 K5 1/2 ton status

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    Mechanical gauges are more accurate and have less problems. Especially with oil pressure it seems. I had nothing but trouble with the sending unit for my electric gauge on a truck I had a long time ago...and the needle would jump all over the place. The mechanical oil gauge on my Blazer now has been trouble free.

    '73 K5
    Chevy good...Ford bad
     
  11. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    The Blow by on the comprssion stroke puts hot air into the water? HUH? Uhhhh the only way that would happen is with a blown head gasket. It would be an escalating thing and not go away. It would climb when ever on the gas. (I Know Supra also, I have a white package 89). You would have it blowing out of the puke tank if it was a Blown Head gasket.
    As for the Chevy...How are your heater hoses routed? It should be intake to the bottom heater pipe. The return line will either go to the radiator or on some it will go to the water pump.
    WHat I think may be happening is there is a hot spot and once the thermostate starts to open it pushe that pocket of hot water past the thermostat giving you the jump. If the Heater hoses are blocked then what may be happen is the same because the coolant in the sytem can't bypass the thermostat and you building presure and it's hold the thermostat closed till it overcomes the pressure. once the pressure drops from the stat opening the stat will operatnormal and never close till cool off so it doesn't get the pressure backed up behind it.
    So are the heater hoses blocked off for the trick to keep the heat down in the cab?

    It's not my damn planet monkey boy!
    <a target="_blank" href=http://communities.msn.com/OffroadK5s>communities.msn.com/OffroadK5s</a>
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    79 Chevy Blazer, Her's
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    Grim-Reaper
     
  12. Itali83

    Itali83 1/2 ton status

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    I just put all autometer mechanical guages in my truck a new 195 stat in it, and the motor is stock, and there is no jumping of temps, something is weird with your motor.
    Ben 87 Jimmy
    <font color=blue>Rust=Bad</font color=blue>
    <a target="_blank" href=http://www.bens87toy.alloffroad.com>www.bens87toy.alloffroad.com</a>
     
  13. Nrose07

    Nrose07 1/2 ton status

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    Ok, I have the identical problem. Always figured it was the themostat opening and closing. The fact I have my mechanical gauge plumed into the intake right behind the thermostat I figured didn't help either. My stock gauge never flucuates since it's in the side of the head. BUT, this has been my theroy, maybe you can help me on it. I have the Vortec heads also, And when I first put them on there was a note in the fell-pro head gasket box about putting Vortec heads on a older block. They said it was a option to drill out 4 new coolant passages in the block to corospond with the revised cooling of the Vortec heads. I didn't want to risk contamination to my motor so I didn't. They were real small holes anyways and I figured I was ok, and some of my other engine builder buddies agreed. But I have always been haunted with the fear that I'm creating hot vapor pockets that are causing my gauge to jump like that since I didn't drill those passages out. What do you guys think?

    Displacement, cubes, and did you say you drive a riceburner???
     
  14. dyeager535

    dyeager535 1 ton status Premium Member

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    As grim suggested, maybe something with heater core. Tried bypassing the heater core yet?

    How about pulling the t-stat and seeing what happens? I'd almost have to expect the problem to be the t-stat with it waiting until reaching 190 then jumping up that high, but a sudden flow of hot water past the sending unit may be happening as well, if there is something weird going on there.

    I'd probably be suspecting sending unit as well though. Its easy enough to change.

    Dorian
    My tech/links page: <a target="_blank" href=http://www.dorianyeager.com/index2.html>http://www.dorianyeager.com/index2.html</a>
    No anti-theft measures on your truck? No pity when its stolen
     
  15. BorregoK5

    BorregoK5 1/2 ton status

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    I've seen a similar problem occur when a 400 ci has a head swap from a 350, the steam holes are missing in the head. This is a classic problem that is frequently overlooked for 400 owners. The vortec head theory with the lack of holes in the block is a good place to start researching.

    What, Me Worry?
     
  16. '73 K5

    '73 K5 1/2 ton status

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    No, the heater hoses are newer and should be OK. Still hooked up to the heater core.
    I think your idea about the hot spot hitting the sensor makes the most sense...since the thermostat is so close to it.

    '73 K5
    Chevy good...Ford bad
     
  17. '73 K5

    '73 K5 1/2 ton status

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    Does your gauge take the reading from the intake or does it go in the cylinder head? Do you have Vortec heads like me?

    '73 K5
    Chevy good...Ford bad
     

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