The article at the link below and the graph inserted from this article suggest a strong relationship between the high temperture high shear viscosity (HTHS) and HP/Mileage. i.e. The lower the HTHS the better the mileage and more HP . I did a check of some of the more common aftermarket oils and also the Motorcraft 5w-20 to see how they compared. It would seem selecting an oil with a higher HTHS than the stock fill would cause a performance degradation. Would you agree? Here are the oils I checked out in ascending order of HTHS. Redline appears to be the worst possible choice. Using a 5w-30 Redline would cost you nearly 2% in HP and fuel milage. The viscosity index (VI) is also the poorest. However, it does have a high flash point (FP) which should translate to less loss of oil due to evaporation over extended oil changes. The Motorcraft as a synthetic blend would appear to be the poorest in FP.
Manufacturer Type & Grade, HTHS, VI, FP (C)
Pennzoil Platinum 5w-20, 2.6*, 160, 224
Mobil 1 0w-20, 2.61, 165, 232
Mobil 1 5w-20, 2.62, 163, 228
Motorcraft 5w-20, 2.65, 161, 185
Amsoil 5w-20, 2.7, 165, 226
Pennzoil Platinum 5w-30, 3.0, 167, 224
Mobil 1 5w-30, 3.09, 169, 230
Amsoil 5w-30, 3.2, 173, 234
Redline 5w-20, 3.3, 145, 251
Redline 5w-30, 3.8, 153, 252
*Pennzoil does not give the second digit accuracy, so order could change as the HTHS could have been as high as 2.64
http://www.iantaylor.org.uk/papers/IMechEFE2000.pdf
Manufacturer Type & Grade, HTHS, VI, FP (C)
Pennzoil Platinum 5w-20, 2.6*, 160, 224
Mobil 1 0w-20, 2.61, 165, 232
Mobil 1 5w-20, 2.62, 163, 228
Motorcraft 5w-20, 2.65, 161, 185
Amsoil 5w-20, 2.7, 165, 226
Pennzoil Platinum 5w-30, 3.0, 167, 224
Mobil 1 5w-30, 3.09, 169, 230
Amsoil 5w-30, 3.2, 173, 234
Redline 5w-20, 3.3, 145, 251
Redline 5w-30, 3.8, 153, 252
*Pennzoil does not give the second digit accuracy, so order could change as the HTHS could have been as high as 2.64
http://www.iantaylor.org.uk/papers/IMechEFE2000.pdf
