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Technical How to reduce under hood heat

Discussion in 'The Hokey Ass Message Board' started by rockable, May 6, 2019.

  1. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
    ALLIANCE MEMBER

    My 41 Plymouth is showing signs that there is a lot of under the hood heat that is ot flowing out. The coolant temperature rises on a mid 80's day and the I believe the fuel in the carburetor boils despite the 1/2" wood spacer and the thick black insulator I put under it. This makes for hard starting when the engine is hot.

    After studying it little, I built it so well that the only air entering the engine compartment is the air being pulled through by the 16" Spal fan and shroud. There is no other entrance of consequence. I have not tried just cutting the fan on at about 180 and letting it run continually but that doesn't seem like a great long term solution.

    So, the only way is see to increase air flow through the engine compartment is to try to create some negative pressure in it. I am thinking about trying to add a couple of "flaps" below the crossmember to hopefully create negative pressure in the engine compartment and increase flow through the radiator. Anyone else ever tried this or any other method for getting the heat out of the compartment?

    Next option would be wrapping my ceramic coated headers to keep the heat from them from adding to the heat load. That should help some. Thoughts? Experiences?

    Last option would be louvers in the hood, I guess but I really don't want to do that.

    Other options and suggestions are appreciated.
     
    Last edited: May 11, 2019
  2. squirrel
    Joined: Sep 23, 2004
    Posts: 42,071

    squirrel
    Member

    Can you replace the electric fan with a mechanical fan? then it would be running all the time. :)

    Of course a post like this requires several pictures, so we can see what you're working with.
     
  3. okiedokie
    Joined: Jul 5, 2005
    Posts: 3,461

    okiedokie
    Member
    from Ok

    I have the shrouded electric fan in my 40 coupe come on at 180 and off at 200 and it handles the heat well even in Oklahoma summer heat with the a/c on. There can’t be much difference in air flow between our cars.
     
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  4. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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    No. There is not enough room for the mechanical fan. The 360 is longer than an SBC. I should have recessed the firewall but thats rear view mirror stuff, now.
     
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  5. gnichols
    Joined: Mar 6, 2008
    Posts: 10,404

    gnichols
    Member
    from Tampa, FL

    No matter how much potential air flow you have at the front, it won't flow if it can't get out so you need to get it up back and out. With no exit, the air just packs into your engine bay and just sits there. Do you have any room for louvers in the rear area of the hood near the bottom of the windshield? Any room for port holes or slots (with nice trim rings?) in the sides of the hood? Could you add louvers in the inner fender wells, at their back edges? Lastly, a hood scoop! A friend added one to his track roadster, that has a full hood and hood sides, and the difference was amazing. It works better at speed than stopped, but he's a happy camper regardless. Before I forget, your toe boards, where the pedals are usually located, are angled 45-60 degrees at the bottom so that they also help draw air from around the engine, down low. If for some reason yours have been squared off, or are full of headers, brake gear, a battery box, etc, different than stock, that might not be helping, either. Gary
     
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  6. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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  7. 49ratfink
    Joined: Feb 8, 2004
    Posts: 17,112

    49ratfink
    Member
    from California

    I think you have the same problem I had with a V8 49 Chevrolet. the wider and low sitting V8 blocks airflow and the heat stays in the engine compartment rather than flowing out under the car. mine was so bad the dash board got hot inside the car.

    the one I have now will not have headers and I have painted the backside of the firewall and under the dash with lizard skin to reduce heat. I also have a louvered hood, but that was not about heat but rather looking cool.

    I say get rid of the headers all together
     
    rockable likes this.
  8. InstantT
    Joined: Aug 15, 2012
    Posts: 601

    InstantT
    Member
    from SoCal

  9. miker98038
    Joined: Jan 24, 2011
    Posts: 382

    miker98038
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    You’re probably on the right track. Almost anyone with a little tbird will tell you to open the hood (it’s hinged on the front) when stuck in traffic. You can feel the heat come over the windshield and watch the temp go down. Don’t know how that helps you solve the problem, but maybe helps you verify it.
     
  10. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
    ALLIANCE MEMBER

    My idea is to add these flaps to create a lower pressure in the engine compartment. They are about 3 1/2" tall and are tough plastic. I would use some stiff aluminum angle to attach them to the crossmember. I remember that Porsche did something similar on 914's. Dont know if it will work but its pretty easy to try.
    0506191653_HDR.jpg 0506191658.jpg
     
  11. I'll say it again...I really like your build. That said, as others have mentioned cut some louvers or scoops into your inner fender wells to help draw some of the air out. I have found the ceramic coated headers generally seem to run cooler than cast iron manifolds so I wouldn't necessarily be running to take them off. As an aside, have you checked to make sure your electric fan is not turning backwards...you wouldn't be the first to make that mistake (I know firsthand! Doh!!).
     
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  12. el Scotto
    Joined: Mar 3, 2004
    Posts: 3,989

    el Scotto
    Member
    from Tracy, CA

    This is exactly what I was thinking. Some kind of heat extractors...
     
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  13. bchctybob
    Joined: Sep 18, 2011
    Posts: 1,539

    bchctybob
    ALLIANCE MEMBER

    I had a ‘62 Jag with a SBC that had the same problem. Incoming air had insufficient outlet area. I cut two 6” Long slits in each inner fender panel and made them into louvers to let air out. It dropped the temp back into the comfortable range.


    Sent from my iPhone using The H.A.M.B. mobile app
     
  14. ojai/jan
    Joined: Feb 6, 2008
    Posts: 89

    ojai/jan
    ALLIANCE MEMBER
    from ojai, CA

    On my 1952 Plymouth Suburban with an early 392 hemi I left out the inner fender panels and it runs cool.
    Jan in Ojai ,CA
     
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  15. gene-koning
    Joined: Oct 28, 2016
    Posts: 1,138

    gene-koning
    Member

    Louvers punched into the back 1/2 of the inner fenders help the underhood air flow a lot. Gene
     
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  16. jimmy six
    Joined: Mar 21, 2006
    Posts: 4,137

    jimmy six
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    Neither the 360 or original engine had a 14" fan.. It's too small. There are some aftermarket with electric motors off to the side and up to 18".
     
  17. Black_Sheep
    Joined: May 22, 2010
    Posts: 798

    Black_Sheep
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  18. AB6DO
    Joined: Feb 9, 2008
    Posts: 48

    AB6DO
    Member

    Do you have air conditioning. If so how close is the condenser to the radiator. If not spaced right, a turbulence is created in the gap, impeding air flow thru.
     
  19. InstantT
    Joined: Aug 15, 2012
    Posts: 601

    InstantT
    Member
    from SoCal

    And probably looks cool, too!

    Sent from my LGLS992 using The H.A.M.B. mobile app
     
  20. tomic
    Joined: Jan 8, 2008
    Posts: 113

    tomic
    Member

    rockable and black_sheep are onto it.

    coming back from the Hot Rod Power Tour last year, after some 6000+ miles, i could see that the radiator output temperature was always too high (i have a sensor in it). top-notch cooling system, plenty of flow, aluminum radiator about twice size, etc. when i got home i did some testing and, long story short, it turns out that air doesn't really flow through the radiator much at all.

    everything i found was sort-of counterintuitive, at first. i always pictured the car pushing down the road and air flowing through the fins etc, but in reality, air's a fluid that finds the shortest way around the obstacle -- the front of the car is one big blunt object.

    the air that does get through the rad has no where to go, because the air under the hood is trapped; the engine, hoses, fenders, wires, etc trap the air, and i found that basically the hot air under the car "sticks" to the bottom of the chassis! air does not really flow through the rad, past the engine and out the bottom. some does, but not much!

    also there were a lot of small gaps, holes, passageways around the radiator; i filled those with blank panels. but this biggest change i made dropped radiator outlet coolant temperature 20 degrees (really, 20) -- i cut two large holes in the hood (nicely shaped, and screened). when the electric fan comes on there's a huge rush of hot air straight UP. i don't mention this as a solution here, but info to diagnosis. (i do foolish things like drive around with a thermocouple DVM taped to the hood.)

    airdams would probably be a huge improvement but again, not appropriate on HAMB, but grist for the knowledge mill.

    rockable's "secret" airdam looks really clever, and black_sheep's louvers kick ass! i might have a spare hood...
     
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  21. s55mercury66
    Joined: Jul 6, 2009
    Posts: 3,271

    s55mercury66
    Member
    from SW Wyoming

    I'm not sure at what speed, but once you reach that speed, it was found that the front tires act as air pumps, so louvering the inner fenders may not have all that great an effect.
     
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  22. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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    My bad. Its a 16 " fan, 2000 cfm.
     
  23. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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    1/2" gap.
     
  24. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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    The lower rear quarter of the inner fenders are removable. Ive had them off before. Didnt seem to help but I will try again. That makes me believe inner fenders louvers aren't going to do it.
     
  25. Do you have room for an oil cooler?

    Cooling the oil will help cool the engine.
     
    rockable likes this.
  26. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
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    Maybe. Thanks for the suggestion.
     
  27. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
    ALLIANCE MEMBER

    Simple, rugged, unobtrusive. Now, lets,wait for a warm day and see if it does anything.

    Yeah, I know. The pop rivets aren't traditional...

    0507191158.jpg 0507191158_HDR.jpg
     
  28. 48 PLYMOUTH HEMI
    Joined: Nov 4, 2009
    Posts: 50

    48 PLYMOUTH HEMI
    Member
    from WV.

    Other options and suggestions are appreciated.[/QUOTE]
    Rockable,
    A couple things come to mind. When I built my 48, P15, I was able to turn the core support around (180 degrees) which allowed me to mount the radiator on the front side of the core support for approx. 2 inches more clearance for the 354 Hemi. This also allowed me to use a fan shrould for the electric fan that also mounted to the core support with its own motor bracket.
    Also I found out that if I had the ign. timing set too far retarded, the engine ran a lot hotter. I also had louvers punched into the inner fenders.
    It does have a bbc water pump conversion that allows me to be able to remove the fan belt between the water pump hub and the electric fan motor.

    Ron
     
  29. Bandit Billy
    Joined: Sep 16, 2014
    Posts: 4,882

    Bandit Billy
    ALLIANCE MEMBER

    I'm digging the air flaps but you are going to be adding more air under the hood, you really need to work on getting it out too. Those air dams up front do work, ask anyone with a C3 vette, tear off the factory spoiler, things get hot in a hurry. But the C3 is also notorious for trapping air under the hood. Hit about 75 to 85 and you have to pop the hood latch to vent the air or your front tires start losing their grip.

    I built several OT '77 trans ams that had working air extractors in the front fenders just for this reason, they vent a ton of hot under hood dirty air. Add something like it to your inner fenders where they don't show.
     
  30. rockable
    Joined: Dec 21, 2009
    Posts: 2,520

    rockable
    ALLIANCE MEMBER

    The idea here is to basically have an air dam in front of most of the engine. (You can't see it unless you get down on your belly and look.) The air pressure on the front will be positive and the pressure on the back will be less positive. That should encourage airflow down and out. At least that is my hope. We will see.

    What sort of air extractors are you referring to?

    I've build a nice looking car and I'm not anxious to hack it up or have to repaint anything, especially on the outside.

    Thanks
     

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