2007 Lexus RX350 Leaking Coolant at Radiator Filler neck where bypass hose attaches. Filler neck found cracked,distorted & brittle from the heat & pressure. Filler Neck made of plastic (Very poor design by Toyota) and incorporating a bypass hose from Filler neck to the large Upper hose which runs below bad design. Also having the expansion tank so far away serves little purpose to relieve any expansion gasses.

I see Lexus/Toyota changed that design with the 2010 up models. Lexus/Toyota should come up with a Service Bulletin to address this problem on the 2007 to 2009 RX350. Better if you made Radiator Filler neck of Aluminium with a O-Ring & attached to the Radiator on a flange with 2-bolts with no bypass hose plus expansion tank closer to the weakest spot filler neck to relieve the pressure in case of cooling system failures. Stop ripping off the consumer, keep it simple.