Changing the PCV to the latest R revision and a switch to 5w40 quantum oil made a big difference in my fuel economy, i can easily get 37-39mpg cruising - i still need to remove my pre cat too
Thicker oil should actually increase fuel economy, not decrease it.
5-40 is thinner than 5-30 at operating temperature. I watched an "Engineering Explained" Youtube video on Oil viscosity and the differences between Fully Synthetic and semi synthetic
No its not. The second number governs the viscosity range of an oil at 100 degrees C. The 5w40 is thicker at a given temperature than a 5W30.
The actual differences can vary from next to nothing to 'quite a lot' depending on which end of the range the oils fall in
Thicker oil logically will increase fuel consumption, but using a much better quality oil helps and in the real world this makes minimal difference. New oil is always better than old oil dirty for lubrication.
At the other end of the spectrum people always seems to think a thicker oil is 'better' as it doesn't get as thin when hot, but this isn't always true. There are so many factors involved, such as wear, tolerances, operating conditions and ultimately oil temperature, climate and so on. Having an oil too thick, which doesn't flow as well, resulting in high oil pressure can be as bad as an oil that is too thin.
