Castrol synthetic or Valvoline?

Phily said

It is odd. But I go from 23 mpg to about 20 sometimes less depending. Almost like the oil has broken down to much and is causing to little resistance or more. Idk it's definitely odd. Running synthetic I should be able to go 5-6k before changing oil and filter. That's why I'm trying the extended stuff. Claims 15k protection. We will see. When I was using normal oil I'd hange it 3k and never noticed a change unless I went about 1-1.5 k over.

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Philly, maybe you know this already, but here goes. I would base my oil changes based on whether the motor is carbed ,throttle body , or port injected, plus the number of warm ups to some degree. I plan on looking up the factory recomended intervals for a carbed version, because that is what I plan to run. Because my project motor will see lots of cold starts ,short trips and is carb equiped, 2500 to 3000 mi will probably be it. My 2015 F150 goes 9,000 miles between changes on the other hand.