Which side of radiator to install electric fan probe?

[Mrturner1]

So I got an electric fan with a Derale performance Single fan controller and it has a 3/8 thread in probe for the automatic temperature fan turn on doohikie. I see on my radiator on the bottom driver side there's a spot where I could thread it in. I can't find any water jackets in my intake manifold, it's an Edelbrock performer if that helps. If I thread it into the radiator I want to make sure it's in the right spot so the fan will kick on when the engine is getting hot. The water leaving the radiator obviously will be nice and cool relatively, so I don't want to thread it on that side but I don't know which is which. Thanks for any help

Matt