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External Coolers - Oil & Tranny

Discussion in 'The Garage' started by BurbLover, Jul 24, 2003.

  1. BurbLover

    BurbLover 1/2 ton status

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    I've been reading in some posts lately that when using an aftermarket tranny cooler, that you still send it through the radiator. Why is this? When I talked with a rad shop about custom bldg one, they recommended against having anything in a radiater. They recommended using just an external tranny cooler for the tranny and an external oil cooler for the oil system. There rational was that by including additional cooling systems into the radiator, it decreases the system capacity of the radiater, in turn causing higher running temps. In addtion, since the internal tranny cooler is on the effluent (cooler) side of the radiator, it raises the just cooled liquid prior to it going back into the engine.

    So, I give you the following questions:

    1 - Would someone care to elaborate on this for me?

    2 - Does this same principle apply to the oil cooler? If not, why?

    3 - If you still use the internal cooler w/ the external one, which one do you run the lines to first & why?

    Thanks in advance for giving me enough knowledge to be dangerous /forums/images/graemlins/grin.gif!!
     
  2. 75-K5

    75-K5 3/4 ton status

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    I belive the general consensus is to run it to the radiator first, then to the cooler, that way you don't undo the work your aux. cooler did by running it through the warmer radiator.
     
  3. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Tranny needs "Some" heat. That allows you to preheat the tranny in cold weather. Even on a GM truck that has the AUX cooler it's still run through the cooler in the radiator.

    Your not putting nearly the load on the cooling system because the tranny is running much cooler. The tranny's in my K5's ran about 150-160 degrees in the pan in the summer with the cooler on it. Only once in 4 years did I manage to get the tanny up to 200 degrees and that was towing a car on a LONG steep grade that semi's were down to 35mph and I was still pulling at 50mph.
    I still haven't installed the sender in the TH400 on my burb but the cooler lines are cool enough that you can wrap your hand around them and not get burnt. So that's under 150 degrees.

    Oil cooler is a seperat animal. It was never run through the radiator. It was always stand alone. I do have the oil temp gage hooked up on the engine in my burb (454) that has external oil cooler. I'm running between 210-230 depending on outside temp and grade. open hwy it seems to stay about 215.
     
  4. HarryH3

    HarryH3 1 ton status Author

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    In later years GM put the oil cooler inside the radiator also. /forums/images/graemlins/shocked.gif My '91 S-Jimmy and '94 Suburban both have the oil cooler in the radiator. I'm thinking that since the engine normally runs in the 190-210 degree range, they just use it to make sure that the oils don't get too hot or too cold. /forums/images/graemlins/cool.gif
     
  5. Grim-Reaper

    Grim-Reaper 3/4 ton status Author

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    Didn't know that. My 95 Vandura Workvan was still seperate.
     
  6. kustom71

    kustom71 1/2 ton status

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    Im a little confused too!On my 99 tahoe i have the factory coolers both oil and trans and i have driven for an hour and then checked my trans fluid and i can touch it without even being burned.now thats highway driving but its also in the summer 95F.so on a cold day i wonder if it ever heats up
     
  7. Twiz

    Twiz 1/2 ton status

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    1 - Would someone care to elaborate on this for me?
    [ QUOTE ]
    There rational was that by including additional cooling systems into the radiator, it decreases the system capacity of the radiater, in turn causing higher running temps. In addtion, since the internal tranny cooler is on the effluent (cooler) side of the radiator, it raises the just cooled liquid prior to it going back into the engine.

    [/ QUOTE ]
    That pretty much sums it up. Allthough, I'd like to add:
    - A liquid to Liquid cooler is far more efficient, than a Air to Liquid cooler.
    - Typlicaly, all fluid temps should hover at or near normal coolant temps (190-210 deg.). Tranny temps will be slightly higher, and engine oil temps will be slightly higher than that. But over-all, at or near coolant temps is a good rule of thumb.

    2 - Does this same principle apply to the oil cooler? If not, why?

    Yes, it applies to the Engine Oil Cooler aswell. The EOC will allways be plumed into the "hot" side of the radiator, engine oil runs hot, aprox 210 +, and should remain relitively hot inorder to funtion properly. (boil out any water that may have acumulated). Current production C/K bodys, S10s, and some other applications are examples of this.

    3 - If you still use the internal cooler w/ the external one, which one do you run the lines to first & why?

    I personaly believe that the hot line out of the trans should run into the external cooler first, then to the radiator. Running it in this manner, should help remove a larg portion of the heat from the fluid, before it enters the cold side of the radiator. Furthermore, The returning tranny fluid temps should be more stable and predictable.
    I'm pretty sure that this is the reverse of the factory installation. It's also the opposite of what A.M. tranny companny would reccomend. So take that, for what it's worth.
     
  8. 88Silverado

    88Silverado 1/2 ton status

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    As was mentioned, fluid is much better at cooling than air. The liquid in the radiator can absorb large amounts of energy (heat) and is much more efficient than air cooling. Why do you think they use liquid to cool the engine other than air cooling /forums/images/graemlins/thinking.gif /forums/images/graemlins/thinking.gif
    Thats why they suggest running it thru the radiator first, (bottom up to top that keeps the fluid in contact with the heat exchanger longer thus absorbing more heat first) than run it thru the external, the air will pull out some more heat reducing temps below the radiator temp. In reality, most radiator coolers are marginal at best. Also cross flow (transverse) external coolers are more efficient than standard "S" tube type.

    In virtually all applications where cooling to remove large levels of heat are required they are liquid cooled (they liquid cool high powered transmitters, liquid cool large power units etc. The amount of cooling that is lost by using an internal tranny cooler is small in comparison to the volume of the radiator. If your depending on that additonal volume to keep your engine cool...your radiator is probably undersized to begin with.

    Yes, the fluid can and sometimes will heat up to the level of the water temp (180-200F) or cool down to the temp of the radator. Normal range is approx 175F for long fluid life. The fluid in the converter can hit well over 250+ degrees from the slippage in the converter (thats why lockups are good and high stall converters play hell on trans. Heat is the number one killer of a trans.
    Trans fluids start to go bad if heated into the mid and upper 200 range.

    At high operating temperatures, the fluid oxidizes, turns brown and smells bad. As heat destroys the fluids lubricating qualities and friction characteristics, varnish begins to form on internal parts (such as the valve body) which interferes with the operation of the transmission. If the temperature gets above 250F, seals begin to harden causing leaks and pressure losses. At higher temperatures the transmission begins to slip, which only aggravates overheating even more. Above 300F, the metals inside the transmission canl warp and distort. Then the clutches burn out and new trans time.

    As a rule of thumb, every 20 degree increase in operating temperature above 175 degrees F. cuts the life of the fluid in half. The approximate life expectancy at various temperatures is as follows:
    175F 100,000 miles
    195F 50,000 miles
    212F 25,000 miles
    235F 12,000 miles
    255F 6,250 miles
    275F 3,000 miles
    295F 1,500 miles
    315F 750 miles
    335F 325 miles
    375F 80 miles
    390F 40 miles
    415F Less than 30 minutes

    Thats why I do a complete trans flush once a year or if the fluid starts to turn brown or smell burnt. Trans fluid is cheap (under $12/case at Costco).
     

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