as above ^
My car has 95000 miles.
My car has an automatic transmission.
According to Pennzoil, synthetic (including blends) and regular oil are completely interchangeable and thus there is no restriction on "switching" back and forth at any time. The main thing of concern with engine oils is that you are using the right viscosity and an oil that has the approved API certification for your vehicle. Fully synthetic oils are preferred of course and have better characteristics all around.
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