Everything is already synthetic except the engine. I changed mine over to schaeffer's supreme 9000 5w-40 and got about .5 to .8 mpg to the better. I have changed my diffs and transfer case to schaeffer's also. Will do the trans at 50,000 miles which will be about another 10,000 miles.
I have switched the motor over to synthetic, no change in MPGs but i also installed the Bypass, so at 15k between oil changes I am gonna save in the long run for that alone. Gonna switch the rest over as i get around to changing it.
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