I'm not sure why you want to shift back to regular oil if you've changed to synthetic. I changed my '01 PT Limited to synthetic at 3,000 miles and wouldn't dream of using anything else (better gas economy (26 mpg (EPA) to 31 mpg- I have a manual transmission) and less wear on the engine (as verified by oil analysis)). I've changed the transaxle fluid to a synthetic one as well, but I haven't done a long trip again to recheck the gas mileage yet. (The first time was after a trip from San Diego, CA to Santa Barbara last September. The following week I went to an AAA car fair in L.A. and verified that my odometer was reading accurately.) If you switch back and forth, you are probably going to negate the effects of a good synthetic because of the extra wear occuring when using the petro oil. Then all you'll do is burn more expensive oil. Even if you've changed your oil per the "B" series in the shop manual (every 3,000 miles), it is probably too late (due to the increased wear occuring when using the petro oil) if you have much beyond 25,000 miles on the PT.)
I've been using synthetic lubes for over 17 years and I won't use anything else. The difference in oil costs is more than made up by gas savings, and wear and tear on your engine/drivetrain. J.L. Warren La Mesa, CA
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