new models such as LS460, GS300, GS460, GS350, GX460, LX570, IS300, ES350, RX350 comes with a TIMING CHAIN, wherein it doesnt need any replacement at all.
But for old models, as per manufacturing standard. timing belt should be change 150,000 KMS or 4 years. Contact your nearest dealership to check whether it was changed or not. Also, see the bearings such as the tensioner, pulleys and the water pump if there's a coolant leak