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.
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?