With 160k on the motor, if you've NEVER run synthetic, there's a few risks involved too. If you have any oil leaks from where the seals are damaged or almost gone, the Synthetic has SO MUCH detergent power that it can tear straight through what's left and leave you with a much more significant oil leak. The best bet for what oil to put in your car is the oil you're using now, and simply change it more often. 2000-2500 miles should keep the oil in the car fresh and clean after the first few changes, as the increased cycle will actually help clean everything out of the engine even better than the engine flush kit stuff does if you give it time.