Remedying a warm 300D Before Atlanta Summer

[MongooseGA]

Hey all,

I've been daily driving my '85 300D for a few months now after a bunch of work done.

Lately, I've been noticing the engine temp creeping up over 100* when sitting in Atlanta traffic. When the car is moving, temps stay right where they should around 80-90*.

I have deleted the monovalve and aux pump with the Klima Design Works kit (highly recommended, I'll do a review later), replaced the coolant reservoir, replaced the thermostat. I did not 'burp' the coolant after the most recent drain and refill, not sure if air in the system can work its way out or if that would be a factor here.

When the temps creep up, blasting the cabin heat does in fact help keep the temps from climbing much higher. Unfortunately, this is a terrible option when the outside temps are hitting 90-100*F+

I did notice a tiny tiny pin hole at the upper hose neck of the original radiator. I have a replacement BEHR to go in but hadn't swapped yet as there hadn't been a need. Guess I'll be doing that now.

I am unable to get out of the car to check if the AUX fan is spinning when the engine temps are climbing and have yet to reproduce it in my driveway. I'm an idiot when it comes to testing electricals but I do have a multi-meter. Any thoughts as to how I can test my fan or its connections? I'm thinking I'll oven/hot water test the new(installed) thermostat when I drain the coolant and swap the rad. Any other thoughts?