pushers dont work with big shrouds because they block airflow. all the factory pushers I see are for ac condensers and are made to be unobtrusive to airflow. I have a MB pusher in the garage, it barely even has a finger shield on it!
so you are maybe blocking airflow with your twin setup. also, make absolutely certain that all the air coming in the front is ducted through the rad core. most overheating problems I see are from having big openings where the air can go INSTEAD of through the core. think of air like a liquid, liquid will go through any opening with the least resistance before going through an opening with even slight resistance. I use plastic and tin to duct the air through the core (tanks dont need airflow)
if you are using a used rad, clean it out. in modern engines having any dissimilar metals, in this case aluminum rad core and iron block, and anything less than 50/50 coolant will cause galvanic corrosion as the heated water flows. this causes sediment that settles in the low parts of the cooling system, usually the rad tanks and in the block. reverse flush both, chances are some sediment will come popping out.
check for trapped bubbles. a pressurized cap means the system under pressure will not boil till well past 212, but only if there isnt a bubble to make steam. usually a bubble gets stuck in the heater (or lack of heater) loop. it seems like I have to drive my truck the first time and let the bubble burp with the expansion tank, after a big temp spike.
make sure you have the right cap and system attached. if its an expansion system, you need the burp line hooked up and an expansion tank with coolant mix in it, because the system will purge air through that line when hot and suck coolant back in as it cools. learned this lesson the hard way the first time by blocking the burp line (hey it was shooting on the engine!) and popping a hose off.
good luck! glad to hear about the 2 minute test turned 10 mile cruise, I have done that myself!
