Natural Convection in half filled Tank
 

Please Help. I am getting AMG:Temperature divergence while running the below simulation

Transient Asymmetric Problem: Natural convection inside oil tank
Laminar ON | Energy ON | Gravity ON

Model:
The simplified model is 1m-Dia & 4m-High Steel tank. The bottom .5m height is filled by oil. And there is 1m of sand below the oil Tank.

Boundary Conditions:
Ambient air is 1F, hence the steel wall is maintained at 1F
Constant temperature of 56F at the foundation, ie the sand is at constant temp of 56F at the bottom.

[Image attached]

TESTS:
Running either Oil&Air or Oil&Sand or Air&Sand with the tank works. Error comes up only when I run all the 3 together.