Cold weather radiator block made of cardboard

Discussion in 'Gen 5 Prius Accessories and Modifications' started by PrimeDan, Jan 24, 2026 at 8:46 PM.

  1. PrimeDan

    PrimeDan New Member

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    With the upcoming winter storm about to make its presence known on the East Coast (along with a full week of below-freezing temperatures) I thought it would be prudent to block my Gen 5's radiator to reduce warm-up time.

    So far, it appears to be working well as I was able to get the ICE up to 150°F with moderate driving in less than 10 minutes with an ambient temperature of 15°F.

    I've attached pictures of my setup. Thanks to USPS for providing their free Priority Mail flat rate boxes!

    2026-01-24 09.34.46.jpg
    2026-01-24 09.34.15.jpg
     
    #1 PrimeDan, Jan 24, 2026 at 8:46 PM
  2. VelvetFoot

    VelvetFoot Active Member

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    I thought the Gen5 had auto shutters.
     
    #2 VelvetFoot, Jan 24, 2026 at 9:50 PM
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  3. PrimeDan

    PrimeDan New Member

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    It appears to have them in general based on what I've seen in the repair manual, but I can't determine whether my Prime SE has them or whether it was/is part of some "cold weather" package/option.
     
    #3 PrimeDan, Jan 24, 2026 at 10:04 PM
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  4. Tande

    Tande Active Member

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    WELL ..... an AI search says, all Gen. 5 have the shutters .......(FWIW)
     
    #4 Tande, Jan 24, 2026 at 11:05 PM
    Last edited: Jan 24, 2026 at 11:11 PM
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  5. KMO

    KMO Senior Member

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    It is part of a cold weather package, so not present in all Japanese market cars, but it's part of the standard 'cold weather package' fitted to all American and European ones. Still, it's not going to be as effective as a block like this.
     
    #5 KMO, Jan 25, 2026 at 2:22 AM
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  6. Mendel Leisk

    Mendel Leisk MMX GEN III

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    You should be cautious, how much you block, and what zones. It'd be best to leave the inverter coolant zone unblocked.
     
    #6 Mendel Leisk, Jan 25, 2026 at 12:36 PM
  7. PrimeDan

    PrimeDan New Member

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    Good point. I've heard that about half of the radiator is used to cool the ICE and the other half is for the inverter.

    I found mention of that in this thread about the Gen 2: Hell -Red Triangle after coolant inverter replacement | PriusChat

    Is this still true for the Gen 5, though?
    113296_Prius_radiator.jpg
     
    #7 PrimeDan, Jan 25, 2026 at 12:45 PM
    Last edited: Jan 25, 2026 at 12:51 PM
  8. BiomedO1

    BiomedO1 Senior Member

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    You can look at the coolant drain valves to get a general idea.

    Like to point out that your putting cardboard over the condenser, so your heat pump won't be working efficiently, also your traction pack cooling system won't be able to remove as much heat. Traction pack is freon cooled in a gen5 Prime.

    It's your thermostat that controls coolant flow through your radiator and truckers only block a portion of their radiator, because they need the additional cooling during the summer months - so they run with an oversized ICE cooling system.....

    It's your car, do whatever you want...... YMMV
     
    #8 BiomedO1, Jan 25, 2026 at 1:02 PM
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