Like this JZJ:
It goes in the upper rad hose. It is plumbed on the low psi side (or at least that is where every cooler I have seen is located). I suppose its design intent is to keep the fluid at a constant temperature. I’ve read where tracks guys have found them not too useful, but for a street car it might be pretty good. I don’t know what temps PS fluid runs at w/o a cooler or with a different one. The track guys report temps far below 200* for their setups. But they have remote reservoirs & coolers – purpose built.