Is it OK to run synthetic oil in the winter them switch back to regular oil in the summer
My car has 195000 miles.
My car has a manual transmission.
You can switch the oil back and forth as much as you want without a problem as long as when you have the oil change done you use the correct viscosity of oil for the engine. There is no reason to change back and forth with the oil types since with synthetic oil you can extend the oil changes from using regular oils by adding about 2000 miles between your intervals when you have the changes done.