Flowing of water problem. [Combustion Engine]

[Exor]

Hello, I am having trouble with flowing of water for combustion engines.

The set up: 12 water pumps > 2 water tanks > 2 combustion engines pumping to take water out of tanks > combustion engines to produce BC power.

The 2 combustion engines pumping water tanks are perfectly fine at all the time. I am using Gold Waterproof Pipe.

After engines turned green, for about 5 mins then water start to drain. Water tanks are still full at the point of draining. Since I have 2 combustion engines pumping water out of tanks so it's fine or is it the problem with pipes?