The Mothership needs an MPG Boost

[Brock]

a 5w40 is not going to give you any noticeable difference as the 5 number is your cold flow and the 40 is your operating temperature viscosity so both 15w40 and 5w40 are going to be a 40 wright while going diwn the road.

I run a 5w30 synthetic. 10w30 is what the new volvo and detroit engines are factory filled with and help mileage... yet again the gains are not super substantial and most on this forum would advise you against it.

a quick change of your transmission and differential fluids to a high quality synthetic will help out.