Must be a dodgy 3 core as all the decent aluminium radiators I've used are only 2 cores but big cores and mine sits on the t/stat and I don't use a fan at all
I can't remember which one you bought. The Alimax ones have a single core but it's 50mm long. The Chinese ones were 3 core. I'm now using the safari spec group 4 fabrication units on the last two cars I prepped.
Something doesn't seem right oz. I've done two forest rally sprints recently on days of low to high 30's with no problems at all. I've got a 14 year old alloy radiator made as a copy off a std 2l one by race radiators in Melbourne. The only time the fan comes on is due to heat soak. No problems idling in start queues or on transports.