Please explain how coolant at 180 degrees can keep my trans fluid below 160. Perhaps I’m missing something in the land of thermodynamics.
I’ve been using a Hayden 11x12 bar and fin style that keeps the trans below 180 all the time. It’s pretty cheap and readily available at both Advanced Auto and Autozone.
That is because going by your vague description of your cooler, you are likely using a 30,000 GVWR cooler which would normally be oversized for a G body that still used the in rad heat exchanger. If you still used the rad heat exchanger, you would only need a 20,000 GVWR cooler. However, you really should be using a 40,000 GVRW with the rad bypassed as you probably only have barely better than stock cooling capacity, could even be slightly worse.
Most trans cooler sizing recommendations assume that the buyer will still use the in rad heat exchanger. The in rad heat exchanger also aids in trans warmup. In general, a liquid to liquid heat exchanger is 33 times more efficient than liquid to air exchangers. Without the rad heat exchanger you will need to run a much larger external cooler.
The rad cooler lowers the ATF to the temp of the coolant on the exit side of the rad, while ths install of an trans cooler further cools the ATF and helps prevent heat spikes. You did not mention your engine and trans type or the intended useage of your car which are additional factors. My CVPI uses both an in rad heat exchanger and a external trans cooler from the factory. It also use a engine oil to coolant, oil cooler.
Also I would suggest against a external ATF filter unless your trans has been modified. Many GM trans only bleed off 10% of the pumped ATF to the cooler through a small hole inside the trans. Unless a rebuilder has enlargered this hole or added extra feed tubes, a external filter can cause excess resistance. Its also why you should never run two external coolers in a series.