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Am I crazy or did switching to 10w-40 lower my MPG?

connor grimes

TJ Enthusiast
Supporting Member
Joined
Oct 24, 2018
Messages
280
Location
Los Angeles
I’ve always run 10w-30 in my TJ but recently got a free 6 quarts of 10w-40 and used it for my last oil change . I feel like my MPG has gone down a bit , living in SoCal temps are averaging 80-95 degrees while I’m driving it . About to change my oil again and go back to 10w-30 and see if it seems to get better fuel economy
 

rouxbicon

TJ Enthusiast
Joined
Aug 17, 2018
Messages
234
Location
Baton Rouge, Louisiana
I’ve always run 10w-30 in my TJ but recently got a free 6 quarts of 10w-40 and used it for my last oil change . I feel like my MPG has gone down a bit , living in SoCal temps are averaging 80-95 degrees while I’m driving it . About to change my oil again and go back to 10w-30 and see if it seems to get better fuel economy

Unless you're a bona fide data nerd who tracks every gallon of gas and has your speedo/odo tuned to <1% error, then no your mpg didn't change. And if there was actually a miniscule change in mpg, changing oil now won't save you enough in mpg to pay for the oil and filter. Change back to 10w-30 at your next regularly scheduled oil change if you like.