Does your recommended (engine) oil viscosity change with synthetic? Based on my 1991 coupe's owner's manual and the temperature range of where I live, I am advised to use 10w-30. I'm assuming in 1991 there wasn't much use of synthetic motor oil among street cars as there is now so this is referring to conventional oil. I currently use napa brand 10w-30 which is rather cheap on the price tag. I have never used synthetic oil before but I am planning to on my next oil change, and I'm most likely going with either mobil 1 or royal purple. My RX7 is a daily driver and is occasionally redlined, about once a week through a few gears, so it doesn't sustain "race like" temperatures for any sustained period of time.

 

You can use a quality synthetic if you want, but it will cost more than conventional.

 

No. It's the same.

 

Correct. If the synthetic has a different viscosity characteristic than the basic oil, match the 2nd half of the number so that the viscosity of the oils is about the same at operating temperature. So if the basic oil is 10w-30, and your synthetic options are 10w-40 or 0w-30, the 0w-30 is the better choice.