Single Grade Ashless Dispersant Oils - No general rule exists for every engine type when choosing the correct grade of oil; however, based on the average ambient outside temperature at engine start-up the most common grades are SAE 40, SAE 50 and SAE 60, which equates to AeroShell Oil W80, W100 and W120 respectively.
Traditionally, the choice is associated with climatic zones - AeroShell W80 for cold climate regions (-17 - 21°C), AeroShell Oil W100 for temperate regions (15 - 30°C) and AeroShell Oil W120 for warmer climates (above 26°C).
It maybe that you have gone from a SAE40 (W80) to the multi-grade. What was the previous oil?
Is the CHT & Oil Temp normal?