flow rate is depended on oil pump construction and dia of gallery, typically oil pump have max efficiency of 55-65 psi. a common rule is for every 1000 rpm the oil pump gives a pressure 10 psi. around 5000-6000 rpm this pressure increases to 55-65 psi but this is not standard for all cars, yet a a very common value. second is speeding up or slowing down of oil flow. from bigger dia to smaller dia, the rate of flow increase ( it's there Bernoulli's theory) and giving angle to oil galleries also reduces oil flow rate, if u see a cutaway model of an engine then at some points the gallery suddenly takes 90 degree turn
oil flow rate is viscosity dependent also, meaning, 0w20 fully synthetic will be less viscous at starting but once it acquires running temperature its viscosity index will increase to 20. at about 40 deg C all oil almost reach higher viscosity index. this temo is achieved immediately after warm up, say 2 minutes. now rest of ur drive is at higher in ternal temperature. now ur 0w20 is at viscosity level 20 and 50w20 (mineral oil) is also near this range because engine is new and internal heat is more
both will have similar flow rate (relatively), thinner oil wont flow early, yet it would be thin in physical appearance absorbing less heat and less contaminants
