Just for the sake of curiosity, does anyone know at what temperature 5w30 and 10W30 flow at the same viscoity? Above some temp they should act basically the same. Below that temp the 5W should flow faster.

 

The viscosity is measured at 100 Degrees C.

So they should both be in the 30wt range at that temperature.

 

So at some point it shouldn't matter whether you use 5W30 or 10W30. For example if it never gets below 32F or 40F. Or are you saying the just below 100C the 5W30 is thinner (easier to pump) than the 10W30?

 

5w30 pumps much better in cool weather than 10w30.

To compare, look at both pour points, and the CCS (cold crank similator) viscosity to determine the best protection.

Basically what I'm saying is stick with 5w30 for all around best protection.

 

If you run your truck like a NYC Yellow Cab, then it doesn't make any difference and in fact, you may be better off using the 10W-30 oil. However, if you let your engine cool off two or three times a day like most of us do, it makes a big difference because the 5W oil will flow better than the 10W at every cold start.