Ideally your transmission fluid should be kept around 175 - 180 degrees. For every 10 degrees hotter than that, the fluid life is cut in half. For example, ATF at 175 degrees can last for 100,000 miles. ATF at 195 is only good for 50,000 and at 215, it's good for only 25,000 and so on. There's no such thing as over kill when it comes to tranny coolers. Especially with a high stall converter. If you don't run a cooler, plan on changing your tranny fluid often.