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Airflow thru radiator

  1. Aug 26, 2009 #1
    Ok hopefully one of you can help me out. I have a 68' bug that I recently converted to watercooled with a 2.0 vw engine with a turbo. I have been trying to figure out a way of effectively cooling the motor. I have a single row radiator approx 26'' X 20". I have mounted it in the back of the car directly behind the motor and I am having problems with it overheating. My reasoning behind this placement was that the basic shape of the car more or less is an airfoil (like an airplane wing) so by placing the radiator at the trailing edge of the airfoil I would be putting it in an area of high velocity airflow. Is my reasoning correct?
     
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  3. Aug 26, 2009 #2

    brewnog

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    It's not surprising your car is undercooling. Think about where the radiator normally sits for a 2.0 VW. Right at the front, behind a grille which has cold air rammed into it with increasing engine speed. When the car is stationary, the cooling fan can take nice, cool air from in front of the vehicle, pull it through the radiator, and then over the engine. With your radiator now being sited behind the engine, any air you can get (and given the layout of a Beetle, I doubt you'll ever get enough) passes over your hot engine (which is radiating even more heat because of the turbocharger)

    With a rear-engined layout, unless you have got a massive scoop or air duct to take air directly to the radiator, I can see cooling being a big problem for you. When moving at speed (with high heat rejection), I can't see you getting the required air flow to cool sufficiently. When standing still, any air you can get will be baking hot.


    Perhaps photos and diagrams of your installation would help us think about the solution, but have you had a look at how the later (water cooled) 911s achieve cooling for heat rejection values far greater than what you're expecting?

    Your basic aerodynamic consideration may be correct, it may be flawed, but the velocity in the general area of the radiator is irrelevant. You need air flow through the radiator both at high vehicle speeds and in a motorway traffic jam.
     
  4. Aug 26, 2009 #3
    Here are some pictures of my set up I also forgot to add that I have a 10'' electric fan pushing air thru the radiator with a thermostatic switch set for 185.F[/ATTACH]
     

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  5. Aug 26, 2009 #4

    brewnog

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    Nice car. I assume you don't have a cover for the setup? I also assume you've checked the silly things, like direction of air flow of your fan (you need a pusher fan for that setup). What heat rejection is your radiator sized for? Have you taken measurements of bottom and top tank temperature during your 'problem conditons'? Are you using the standard water pump?

    I can't really see how you've made provision to take cold air to the radiator, other than whatever air is incidentally in the vicinity (and that'll be bloody hot, being right next to the engine). If you haven't got a healthy 'ram air' effect, you need a fair old fan, and yours might not be man enough.

    Assuming all that is addressed, I would suggest you look at enclosing and ducting the radiator.
     
  6. Aug 26, 2009 #5

    brewnog

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    Incidentally, I've recently bought a shed of a 1977 911 and have been idly thinking about how I would (hypothetically) put a water cooled engine into it. I've come to the conclusion that I probably wouldn't bother, and that there's a fair reason many rear engined vehicles are air cooled.
     
  7. Aug 26, 2009 #6
    Oh lol I didnt even realize you were the same person on the other thread. Yes, enclosing the radiator and making some sort of a scoop would help Im sure and is part of the plan in due time. I was just wanting to ask anyone with aerodynamics experience if I actually HAVE airflow back there, it would be a bit pointless to build a scoop where there's no air.
    I do have a pusher fan (zirgo I believe, something like 900cfm) although I have heard that the ford mustang and T bird fans move a little over 2000cfm so I might try that if all else fails. I know that the best place would be in the front of the car, problem is, just as in your porsche, its a pan car, so there isn't much place to run coolant lines. I will tell you though that moving from an aircooled to watercooled motor makes a BIG difference in performance, this thing absolutely SCREAMS! Third gear wheelspin is common :)
     
  8. Aug 31, 2009 #7

    brewnog

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    No, I'm not the same person in the other thread.

    Does your engine overheat when you're driving hard, or sat in traffic? Do you have details for any of the other questions I raised, or do you just know it's overheating because your pressure cap is popping?
     
  9. Sep 1, 2009 #8

    Ranger Mike

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    when i was researching the diesel VW super beetle i bought last year, i found a guy who got 65 mpg with his VW,,,had a rear top spoiler attached and aeroed the VW to the max,,,
    in my opinion the radiator will not get enuff air mounted as it is. we race a 2000 cc 4 cylinder and use two aluminum radiators..no fan..just side mounted core on each side of the formula car..i recommend a two core design as a minimium..you need a fan for idle time at traffic lights and in city driving...
     
  10. Sep 4, 2009 #9
    No cover yet, Im planning on fabbing one up soon though, the direction of airflow if correct, the fan is a 12" pusher moves something like 900cfm. Radiator is from a 2.4L 4 cyl. of 150HP. I am using the standard water pump and it is flowing water. I am thinking that the radiator is in a giant "hole" in the back of the car. It stays plenty cool in traffic or below 50MPH but above that it starts to get hot. What I may do is mount a different radiator horizontally in a wing at the back like porsche does with their oil coolers. It would be nice to know where the air is flowing around the car so I can just place the radiator there without all this guessing.
     
  11. Oct 18, 2009 #10
    like somebody said, it's no surprise the car or the radiator is undercooling. radiators need cool air to hit them for heat exchange, the cooler the air the better. From the picture, that radiator is almost useless. first of all, pull that radiator away from the flow path of engine bay heat; you can put it on top of the engine, although not the best, and put a well sized scoop to collect air towards the radiator, and dont forget an enclosure to give the air no option but to go through the radiator. You can also put it underneath the engine if you have space!! which i doubt you do... Still the best option is putting it in the front. In a friendly tone <get off your *** and do it right the first time> LOL when it comes to cars, you can do it now or do it later, so do it now and save yourself some time and heartache, and at the end you have a car that will take abuse for more than 10 seconds. And, it's really not much pain, all you need is few elbows <home depot unless you want show looks>, oval or rectangular piping to run under the car, the biggest rad you can get your hands on, and go to town. While youre at it, put and intercooler back there. I road race my daily driver and i had a long bout with overheating since my intercooler is shielding my radiator from cool air, after a lot of r&d, undercover scoops and ducts are my best friend. Now the lexus (SC300) overtakes Z06's and porsches, still i keep on going while they have to stop to cool down.
    Goodluck on your project..
     
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