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Way to reduce under hood temps?

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  • Way to reduce under hood temps?

    Will raising the windscreen end of the hood/bonnet help lower engine bay temps ?
    First hand experience appreciated

  • #2
    No experience, but general consensus and physics says that makes it worse. You'll want a vent on the front side of the hood between the radiator and engine. That will lower underhood air pressure (vs your plan that raises it and makes the air stagnate in the engime bay) and help the radiator flow better as well as get that heat out. If you have a turbo or are concerned with exhaust manifold heat, you can vent that separately.


    • #3
      From reading previous posts here that's a high pressure area so the air in that area is going to try to force it's way into the engine bay while the air from the front of the car is trying to go the the front of the engine bay. Both fighting eachother will make less airflow.

      Alot of guys here have vented hoods. If you go through their builds you'll see alot of the amazing things the bought or fabricated to lower under hood temps. There's even a vented hood thread somewhere here.


      • #4
        Thanks guys .I have been told that it was/is a hi pressure area at the bottom of the screen as well.


        • #5
          A vented hood would be the best solution in my opinion.

          Most of what I've read about using spacers under the hood hinges to prop up the hood near the windshield says that this method of venting is really only good at venting hot engine bay air out when stopped or at very slow speeds; anything above this and (like Cdlong and Clotuning said) I could see how the outside air would be competing or preventing the engine bay air from escaping.

          I would be interested to see if (and how much) putting a little "flap" (like a Gurney Flap or some call it a "wickerbill") along the back edge of the hood would allow the "rear-propped" hood setup to evacuate the air better than without the "flap".

          Someone correct me if I'm wrong, but I believe the reason air pressure is so high (at speed) at the bottom of the windshield is because the airflow is making a somewhat sharp transition from the almost flat hood to the ~35 degree windshield; and where this transition takes place is right where the air would be "trying" to escape out from under the hood? Perhaps a Gurney flap along the back edge would help move this high pressure point forwards, away from the bottom edge of the windshield, allowing a larger "pocket" of low pressure for the air to escape from under the hood? hah I dunno.

          Last edited by cleantune; 09-13-2015, 11:39 AM.
          "A pessimist thinks the glass is half-empty, an optimist thinks the glass is half-full, an engineer says that glass is twice as big as it needs to be"
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          • #6
            If you're having problems with heat from the turbo area, you can install louvres on the hood above the turbo area. With the louvres it should pull the hot air out of the bay. Without louvres (i.e. just a hole) I think it would be high pressure in the area so air wouldn't be sucked out of the bay.
            Hood vent behind the radiator is where I'd start though.