I don't see the answer, so here it goes...
When using an engine with conductive pipe, you absolutely need a stone or gold conductive pipe after the wooden one.
I don't quite know why, but that is how BC work, and it has been so for quite a while.
So, either place your engines directly near the machine, or use stone/gold conductive pipes between the wooden and the machine.
EDIT: And no, biogas engines don't need to cool down, it's the reverse.
They need to heat up with a bit of lava if they have cooled down too much.