switch back/forth from Synthetic to Conventional

Shouldn't harm anything.

There were some compatibility issues with earlier synthetic oils, but all of that was solved a long time ago.

--scott

A couple of thoughts:

1. A lot of variables can affect gas mileage -- including seasonal changes in both driving style and the formulation of gasoline. It's a hard experiment to control properly.

1. Not all synthetic oils are rated as energy saving -- and some dinosaur oils are! Although synthetics are often perceived as being more slippery, that isn't the only issue. It has more to do with viscosity and formulation than with feedstock origins. It is also supposed to be interpreted as a fleet average rather than as a guaranteed result in any particular car. Finally, it is only one or two percent at most -- one of those factors that are a big deal societally but not necessarily apparent, let alone important, to the individual consumer.

I think you've appraised the situation correctly Synthetics are better, especially in hard service -- but you can get a good long engine lifetime out of a conventional oil if you change it, w/quality filter, on an appropriate schedule.

Best of luck,

--Joe