Has any work been performed on the cooling system recently? Where do you hear the bubbling coming from? Are you observing a temperature gauge or warning light that is concerning? Do the cooling fans turn on when you turn the air conditioning system on?
RepairPal Certified shops can diagnose and repair your 2003 Lexus GS300. They provide transparent pricing with a minimum 12-month or 12,000-mile warranty on repairs and services.