Radiator hot on top, cold on bottom

Discussion in 'Heavy Duty Diesel Truck Mechanics Forum' started by James P, Sep 17, 2021.

  1. James P

    James P Bobtail Member

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    My detroit 60 series 12.7. Just had rebuilt, new radiator, water pump, 190 thermostats new hoses too. But still radiator is hot on top, cold on bottom. Any ideas??? Thanks
     
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  3. AModelCat

    AModelCat Road Train Member

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  4. lester

    lester Road Train Member

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    That's kinda how it's supposed to work. Goes in the top hot and comes out the bottom cooler.

    Is your engine temp running too cool?
     
  5. James P

    James P Bobtail Member

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    No. Getting hot on long pulls. Radiator should be same temperature from top to bottom. Kinda like flow restriction
     
  6. AModelCat

    AModelCat Road Train Member

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    This radiator, does it flow top down, or is it a crossflow.

    Top down it HAS to be cooler on the bottom. If its the same going in as going out, its not cooling anything. I'd be considering an airflow issue in that case.
     
  7. James P

    James P Bobtail Member

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    When I changed radiator. I could blow through CAC, ac condenser is new as well. This is a 91 Freightliner. I'm just at a loss. Our 96 Freightliner, the radiator is same temp up and down
     
  8. James P

    James P Bobtail Member

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    The 96 has same radiator, same set up. Both hoses from reservoir are new. You can blow through each one as well
     
  9. Lazer

    Lazer Medium Load Member

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    Radiator are designated to cool the coolant. The liquid exits, cooler than when it entered. Is it the radiator itself that is cooler (or not), at the point that the coolant exits? Or are you checking the temps on the hoses?
    Look at the directions of the fins, do they go up and down, or side to side?
     
  10. bad-luck

    bad-luck Road Train Member

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    That is actually normal, what problem are you having?
     
  11. AModelCat

    AModelCat Road Train Member

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    I think he said it was overheating during a pull.

    I'd check that all the shrouds are in place, air can flow through easily (no folded fins, dirt/debris collected on the core etc). Fins will start detaching from the tubes over time. That will reduce cooling efficiency as well. If fan was removed, was it installed backwards?

    Rads can collect rust/scale on the inside of the tubes. Acts as an insulator and prevents heat transfer from the coolant to the core and then to the passing air.

    What's the coolant mix ratio? Running straight coolant is a big no no. It will cool much worse than 50/50.
     
    Last edited: Sep 19, 2021
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