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Transmission cooler

Discussion in 'All Other Transmissions' started by 1994ch, Aug 9, 2016.

  1. 1994ch

    1994ch Active Member

    Dec 6, 2008
    South Carolina
    The other day I swapped out the radiator and had trouble getting the transmission cooler line fittings to fit in the new radiator. So since I was at the shop and had to get home.... and its the only vehicle I have, I just by passed the radiator and so it is running on just the external cooler up front.

    So my question is how big of a priority should I make of getting back in there and finding some fittings that will work? I have heard that the main thing the radiator cooler does is actually warm the trans fluid up to operating temp faster. Is this true?
    I assume I am fine running short hops to and from work but if I went for a longer trip through the mountains does the radiator cooler do much to keep the temps down?

    Thanks for any input,


    May 9, 2008
    Slow speeds are the WORST thing to do when the radiator cooler is bypassed. The cooler out front only really works when you're moving, so at slow speeds it doesn't do much of anything. The primary purpose of the cooler in the radiator is to maintain the trans fluid in a range to keep it warm enough to evaporate out any mopisture, but still keep it cool at slow speeds where the external cooler isn't very efficient. So I owuld make it a priority if it was mine.
  3. tanman_2006

    tanman_2006 Just a farm kid...

    Feb 15, 2010
    Seiling, Oklahoma
    The inside radiator cooler basically stops the atf from going over 200 when in slow traffic. This puts more load on the cooling system this is why a clean cooling stack and good fan and fan clutch are important
  4. Will L.

    Will L. Well-Known Member

    Jan 25, 2013
    Boulder City Nv
    You have to go with the above answers as to why, but i've mentioned many times in fleet we would run trans 250-300,000 without fluid and filter changes on trucks that didnt tow much of anything.
    We did do some experiments of bypassing the radiator coolers. Smoked brand new trans in less than 20k.

    A couple days maybe, if you have to- I wouldnt do a week unless that truck was going on auction block.
  5. 1994ch

    1994ch Active Member

    Dec 6, 2008
    South Carolina
    Thanks for the info.... Makes sense, will get that done today for sure then.
  6. floyd400

    floyd400 Member

    Nov 14, 2013
    Northern Indiana
    I'm considering adding an external trans cooler to my 84, I want to go with the biggest cooler I can fit and there's plenty of room on my truck. I was going to bypass the radiator cooler to reduce the heat load on the radiator but that's a good point about keeping temps in check while not moving/moving slowly. Hadn't thought of that before, makes me rethink my plan.
  7. FellowTraveler

    FellowTraveler Well-Known Member

    Sep 29, 2014
    Nature Coast
    Yep, as the torque converter slips to stall speed temps can climb too 300 deg f. at the trans line to radiator. As FERM mentioned airflow over an aux cooler isn't best in stock configuration mostly because of air gaps around radiator and it's support, missing fan shroud will compound the problem.

    Hot trans fluid getting cooled down by engine coolant is a good thing then the aux cooler just makes it better.

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