No fluids have "fuel_value" tag, even ones that should be burnable

[Reika]

This means that any mod that wants to allow a fluid power source, running off, say, the oil products, needs to impose such a value itself. This soon results in a mess of six mods assigning 12 conflicting values to four fluids. Sure, the result of that is still burnable, but five of those mods end up with their numbers rather seriously out of balance.

[posila]

Since there is no way to burn fluids in vanilla, vanilla fluids not having a fuel value is obviously not a bug.