Why/How is this leaking heat?

[Sleeeeeeeeeeper]

The steam/window tile is currently around 180c. The petroleum coming in is around just shy of 100c. Steam is also 180c (since it's generated by the pH2O from petroleum generator) and around 20kg/tile.

The whole thing just keeps dropping temperature very slowly. Why? I don't understand where/how the heat is leaking? 

[blakemw]

Without knowing all details hard to say, but here would be my speculations:

1. Heat leakage into the insulated tiles, assuming they aren't made of Insulation any insulated tile will absorb heat, particularly from gas, as gas has a 25x heat exchange multiplier with solid tiles. This can be solved by "double-walling" where the inner wall is ideally a tile with very low thermal mass (e.g. gold or lead metal tile) and the outer layer is insulated tile. This would achieve actually zero heat transfer with Igneous Rock or Ceramic insulated tiles due to certain temperature thresholds being required to actually exchange heat between a solid tile and an insulated tile (these thresholds also exist for gas, but the 25x multiplier means if the threshold is 250 C for Igneous Insulated:Solid Tile, it's only 10 C for Igneous Insulated to Gas).
2. Heat being absorbed by the petroleum while it flows through the insulated pipes and while it sits in the petroleum generator, this can't be entirely prevented (without mods) except by using Insulation to make the insulated pipes, but it can be minimized by as much as possible embedding the insulated pipes in insulated tiles and minimizing the length exposed to the steam. The heat exchange between the petroleum sitting inside the petroleum generator and the steam is harder to eliminate in the normal game, but since you are clearly using a mod, you can place an insulated tile over the bottom-middle tile (that's the tile the "bottle" of petroleum sits in) to insulate it.

[Sleeeeeeeeeeper]

Ah okay. I'll try them out thanks.

Buildings inside tiles is not a mod btw. You just need to lay down a tempshift plate -> plan a tile build + then a building -> proceed to build both. It's an in game exploit.