mobile 1 AP 5w30 to Amsoil SS 5w30, lower mpg?

Messages
391
Location
MD
Hello, I had my Maxima 2009 since October 2018, was at 80k miles on the odo. 1 owner. Previous owner used Nissan conventional 5w30 all the 80k he drove, I have all records, he used to change it every 4k miles. In November I had the oil changed to my favorite, Mobile 1 AP 5w30 synth with Mobile 1 m110a filter. I ran that for about 4k miles (short trips, cold weather, excessive idling) and then changed with Amsoil SS 5w30 and mobile 1 filter. With Amsoil I noticed 1 to 2 mpg loss (22-23mpg to 20-21), other parameters all about the same, tire pressure, routes, congestion, driving habit, speed, etc... I measure mpg using miles driven over gas pumped, I have a log of every tank fill up and mileage. Is this loss of mpg a concern that mobile 1 performed better for my engine? Engine is very smooth and quiet either way (Amsoil maybe slightly quieter), doesn't burn or leak. Overall in very good shape. Thanks
 
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Messages
437
Location
Canada
Mobil AP is actually thicker @ 100c, so it should be the one less mpg efficient. But it would be so little that it would be negligible. The difference is most likely in driving style.
 
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If you averaged this out over several thousand miles, you would likely notice nearly any difference at all. Do you use Fuelly? That being said, it's not surprising since the Amsoil is both a little thinner at 100*C but has a higher HTHS. To me, that would be why your engine "seems" quieter on Amsoil. If you want, PM me your fuel log and I will run it through some statistical tests to see if there is any difference, and if so, how big it is. I would not say either one is "better" just based on a small sample size of slightly different fuel mileage. If you're looking on keeping the car for a long time, I'd much prefer better protection over a small increase in mileage.
 
Messages
16,601
Location
Upper Midwest
The energy density of gasoline varies even at the same gas station, up to 4% or so (aside from winter/summer blends). That's most of your difference right there. Measurement of something is only the beginning, attributing it to one isolated variable is the key. Entirely impossible in the real world given that the difference between motor oils of the same grade is deep in the noise.
 
Messages
35,466
Location
NY
I doubt without some very sophisticated testing equipment in a controlled environment the difference could be calculated. Especially when we're talking the same grade oil.
 
Messages
151
Location
Northern Michigan
I have never been able to detect an mpg difference between brands or grades of oils? Now mpg difference in rain an/or snow vs dry, wind or no wind, summer vs the cold of winter....yes I have seen differences.
 
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