Oil + additive viscosity

Hi guys. Just a stupid question I would like to pur out there.
I am wondering if I mix 4 liters of 5w30 full synthetic oil with 1 liter of Lucas oil stabiliser, can I find out what viscosity the outcome would be. Just putting it out there if anyone may know the calculation etc.
Regards.
Billy D...


The viscosity index will approximately be... slippery oil in the motor that won't know the difference.
Spend your time in other trains of thought.
Live long and prosper.