Using latest release versions of Immersive Railroading, Universal Mod Core, Track API.

Using the detector augment, call the info() method while a fluid tank rolling stock item is above it, and inspect the resulting table. You should see the fluid_amount value is always zero, despite the fact that the tank is in fact full.

It'll be fixed in the next release

Seems like the code right now will always give

fluid_type = nil
fluid_amount = 0.0

because some code here is commented out https://github.com/TeamOpenIndustry/ImmersiveRailroadingIntegration/blob/168b77071eecae209d3f19bcf348c2c47742eeb9/src/main/java/cam72cam/immersiverailroading/thirdparty/CommonAPI.java#L43

Which will mean that getFluid() always return null, and the have the code at https://github.com/TeamOpenIndustry/ImmersiveRailroadingIntegration/blob/168b77071eecae209d3f19bcf348c2c47742eeb9/src/main/java/cam72cam/immersiverailroading/thirdparty/CommonAPI.java#L97 always return nil and 0.0