mods: efan, superchips 87 performance with custom trans tuning, sonnax, Hipotek throttle body, k&n CAI, single to dual magnaflow, synthetic changed every 6k or 6 months, 180 t-stat...feather or flat out I average 16 - 16.5 MPG all the time (with the exceptional trip, 18 maybe 19). This is 45 mile round trip, 40 of that cruising at 70 mph. I would love to see 25, even 20 regularly, but it aint happenin in my truck.

 

Its a truck..sure your BMW M5 can go 20,000 miles between oil changes but when we're talking about an American V8 and the driving habits of most of us here gearheads on the forum..synthetic or conventional that oil will not mind being changed at 3,000 miles. If you want your engine to last, changing oil consistently is key. I don't believe in doing 7,500 mile intervals on my truck just because I am running synthetic. When I used to run conventional I would usually end up changing the oil before 3,000 and I just started running Castrol Syntec 5w-30 last oil change. I still plan on changing it at my regular 3,000 mile interval unless for some reason I didn't have the money then the maximum mileage I would do is 4,500. Using Castrol ends up being about a $50 DIY oil change but I am a firm believer in the saying "You get what you pay for."

 

is it true that oil starts to loose lubricating property if the vehicule is not mooving after 3 month?

 

I hate to burst your bubble, but from what I found out castrol syntec 5w - 30 is only group 3 while it is synthetic, it's not a "true " synthetic like group 4 or 5. So your not getting what you think your paying for. A full synthetic is worth the money.
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Mobil one is a true synthetic right? And ps I change mine for like $30