+1 for the crossflow idea, think the desert coolers have triple pass , also about 700$
but i noticed with my 52mm the bulk of the water just flows through one side of the radiator, meaning the passenger side isnt really doing alot..Even if you rev the sucker (and i revved it to 6k) not alot pushes across because the tubes are so big they flow it all straight down..
Is it dual core?
Of course thats sitting still, bit hard to see what its doin on the move, but could still be an issue
I reckon having some kind of diffuser at the top inlet that even sent half the fluid to the other side of the radiator could be of some good
I drew a crappy pic of the top tank to give you an idea what i mean..
eDIT>.Yeah or dud cap... mine came with 1.1 but think standard is 0.9