Originally Posted By: BerndV
Originally Posted By: MGregoir
A 10W oil has the same pumpability as a 10W oil with set limits for each grade, a 5W oil is automatically better than a 10W oil.
So does this mean that a 5W dino will always flow better than a 10W synthetic down to their respective pour points.
Assuming things are somewhat linear.
10W oils are rated for cold cranking at -25, and pumpability at -30.
5W oils are rated for cold cranking at -30 and pumpability at -35.
The pumpability limit is 60,000 cP (although few oils breach that). That is also called limit pumping viscosity.
The bare minimum standard 5W-30 will be 6600 cP cranking at -30, where the bare minimum standard will be 7000 cP at -25. 0W oils are 6200 at -40, so the standard becomes stronger with each temperature range, and because viscosity is somewhat logarithmic, a 5W oil's cold performance will always beat the 10W oil's, and the lower the temperature the greater the gap will increase. If the 10W oil were as good as the 5W oil, it would be rated as a 5W oil, simply put.
The 10W synthetic may still pour. The points where this becomes significant are in conditions few see, which would be starts with no block heaters at -30 Celsius or lower.