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My "new" 1990 350 is overheating any suggestions?

Discussion in '1973-1991 K5 Blazer | Truck | Suburban' started by shum1, Oct 19, 2000.

  1. shum1

    shum1 1/2 ton status

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    My \"new\" 1990 350 is overheating any suggestions?

    First, thanks everyone in for all the help with my other problems.
    Well everything was going well until today, It was a 70 degree day but I used the ac. I accelerated hard and I overheated to the point where coolant was going into my overflow. The temp gage went to around 215. The past owner said he just replaced the water pump. I have a serpentine belt, is there any way he used the wrong one? It is hooked up correctly it seems, I realy dont feel much water flowing thru the top hose (should I)? What direction does the water flow? (top to bottom? or bottom to top?) What temp should the gage read under normal to hard driving conditions? I'm thinking themostat. Could the cap cause any probs? Should I have the radiator serviced? Thanks again. 1990 sub w/350 tbi stock.
     
  2. Sparky

    Sparky 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    It is hard to pinpoint the problem with the information you gave us. Does it overheat when you stop or is it just dependent on the load you put on it? There is not too many things that can cause it to overheat. It could be a lack of fluid, bad pressure, or lack of circulation. The OEM (original equipment) thermostat should be 190 degrees, and if working properly, under any driveing conditions it should keep the water temp very close to that. They are not expensive or hard to replace so it is a good idea to just replace it as routine maintanence. The radiator cap can also cause it to overheat if it does not hold any pressure. Run your engine untill up to normal operating temp. Shut it off then stand next to the cap and listen for any hissing. If you hear any it means your cap is letting pressure out so replace it. Again, if in doubt just replace it. It is very cheap and very very easy to replace. If it overheats while stopped there is a good possiblity you have a bad fan clutch. This is because there is not enough air getting pulled through your radiator to cool the fluid. While you are moving plenty of wind pushes air through so it is not a problem. Also, do the obvious and check for any leaks. To anser your question... You probably cant feel the fluid move through the hoses, espessialy if it is cold. The fluid runs into the engine from the bottem of the radiator and out of the engine from the top. The thermostat wont let any water back into the radiator untill it is warm. That is why you wont feel the top hose get warm untill the thermostat opens up. If anything clogs the thermostat you will have limited flow which can cause overheating as well. Hope I answered your question. Sorry for the book. To sum it up... I would replace the thermostat and the cap. See how it does, and then look at the the slightly more serious items such as the fan clutch and water pump. Good luck!

    Sparky

    78 K-5
     
  3. EDdaTREE

    EDdaTREE 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    First I'd change the cap and thermostat, unless you'd rather just find a shop that ain't gonna hose ya...fifteen bucks in parts and you will know that at least those parts are new. Then I'd start wondering if the clutch fan is bad..shake it and feel for play in the bearing, was it hi or low speed when it overheated? You actually don't even need a fan above 35 so thats the idea behind clutch-type fans. Have a pressure test run on the system and also see if the coolant looks like ca-ca. Belts tight? Running a fan shroud? etc.
     
  4. shum1

    shum1 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    Thanks a bunch Sparky for the reply, Ill do as you suggest and get back to you, later.
     
  5. sosamantx

    sosamantx 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    <font color=blue>While you are changing the thermostat and the cap, look inside of the radiator (where you took off the cap) and see how much corrosion has built up around the tubes. It might be time to have it rodded out. Around here it is about $40-50 if you take off the radiator and take it to them. If you do as the others have said and you still have problems, you might also consider a high flow thermostat that opens at the same OEM temperature. Also, when you take off the radiator cap and run the motor till it is warmed up, does the coolant seem to be flowing? You might have to give it a little gas to see it flow. Anyway, that's my 2 cents worth. - Steve</font color=blue>

    <font color=blue>Steve Sosa a.k.a. "sosaman"</font color=blue>
    http://sosaman.home.texas.net/carpics.html
     
  6. WhiteWhomper

    WhiteWhomper 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    Since I did not see it mentioned, do you still have on the fan shroud? You would be surprised to see how many overheating problems are caused by a missing shroud. If you don't have one it is well worth the money to pick up at the local boneyard.
     
  7. Chewy

    Chewy 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    If all else fails drill a 3/8 inch hole into the thermostat itself. I had an overheat problem with my 87 and drilling a hole to relieve the pressure solved the problem. just a suggestion.

    '87 Beast
    Colorado, USA
     
  8. shum1

    shum1 1/2 ton status

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    Re: My \"new\" 1990 350 is overheating any suggestions?

    Well, I replaced the thermostat w/ a 195 degree one, I put a new 16lb cap on her and things have calmed down quite a bit. The coolant is no longer bubbling up into the overflow res. The temp gage show around 212-215 when going slow uphill w/ ac on at higher rpms and then cools off to around 195 at highway speeds, does this sound normal? Yes I do have a shroud and no mods whatsoever. Thanks.
     

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