Hey Tim,
Looks like you're on the right track...
Another suggestion: Get rid of the flow meter (if you really have to have it, put it on the discharge side of the pump - you don't want anything restricting flow on the suction side). With good air flow moving thru your radiator you should be able to see -20 to -30 C on the cold side (depending on how cool your ambient air is).
Good luck,