You can smelt down Magma Cream in a Smeltery Controller from Tinkers' Construct. The required heat for it is 0C.
The liquid you get, Liquid Magma (from Extra Planets) then should be able to be used as a fuel source, says the JEI. While it does seem to show up in the Controller if I put it into the Seared Tank, the heat that liquid has seems to be even less than 0. It says 0, but smelting more Magma Cream while that liquid is set to be the source in that Controller throws an error of "not enough heat".
You can smelt down Magma Cream in a Smeltery Controller from Tinkers' Construct. The required heat for it is 0C. The liquid you get, Liquid Magma (from Extra Planets) then should be able to be used as a fuel source, says the JEI. While it does seem to show up in the Controller if I put it into the Seared Tank, the heat that liquid has seems to be even less than 0. It says 0, but smelting more Magma Cream while that liquid is set to be the source in that Controller throws an error of "not enough heat".