I have a 93 accord 5sp with 215k , was thinking of switching to amsoil synthetic oil. I have heard that you should not run synthetic in a high milage car. I have always ran Castrol 5/30 and have had very good service. But I think this might improve my fuel MPG.

 

I've never heard of changing to synthetic to improve gas mileage. Where have you heard it?

My advice is to stick with what you've been doing, though you might consider the "high mileage" motor oil (though honestly I have no idea what the difference is between that and the regular stuff).

In the meantime... make sure your tires are property inflated, clear out any unneeded stuff from the trunk that you've been hauling around (to reduce the weight), don't make quick starts and accelerate gently, and the best way to save gas is to carpool and avoid unnecesary trips.

 

yes, syn will improve mpg slightly because it tends to be thinner than conventional, even with the same viscosity ratings. next time, please search before you ask questions on motor oil because there are ten million threads on this subject, thanks!