temp results of adding hot liquids

hi

we have two compressors hp and lp driven by motor and between the driver motor and the lp compressor there is gearbox .

the sequance of the equpiments like this:

bearing1 - driver motor- bearing2-coupling- gearbox-coupling-bearing3-LP Comp- bearing4- coupling- bearing5- Hp Comp- bearing6

the outlet lube oil temp for bearings 1 to 6 are 146 F, 146 F, 147 F, 153 F, 145 F, 137 F.

the outlet lube oil for the bearings meet in 1 line then go inside the lube oil reservior.

my quastion is what will be the temp of the oil inside the reservior?

i think it will be logically below the maximum temp of the bearings and it will be the mean of these tempreture.

my supervioser said no it should be above the maximum temp?

how can we calculate the temp of reservior assuming that the pressure and the flow rate are the same for all the bearings? any formula