Cooling system for a P-40F/L went a bit over 300lbs, each plane varied a pound or two. Please note that the Merlin and Allison required different sized radiators and oil coolers.
Cooling system for a Merlin P-51 was given as 663lbs.
Oil system weights are given separately.
System weights would include actual radiators, lines, header tanks, coolant, and pumps.
In the case of the Mustang no separate weight is given for the intercooler/after cooler so one assumes that was part of the cooling system.
Bombers might have bigger radiators/more coolant to handle long slow climbs at low airspeed. Speculation on my part but climbing almost always was a more difficult problem than high speed level flight. If you are doing 360mph in level flight you have twice the air going through the radiator than you do at 180mph climbing.