QFT, I had 4 combustion engines pump 30 minutes non-stop into a full cell trough some conduits, nothing exploded, nothing overheated, conduits drop the excess.
They work that way with BC engines but not with TE.
In BC the cables explode and the engines only if you send too much power through them (since you can power engines with engines), and of course the combustion engine explodes if you let it run out of water. However the engines to not explode if they can not get rid of their energy. They basically just waste it. BC engines are dump enough to happily pump energy into a full machine without ever complaining (at least if connected directly and not via conductive pipes).
TE is a bit different. Although the cables can never explode the engines stop working. And need a whack with a hammer. For Magmatic engines the solution is simple. Connect at least one magma-crucible to your network that turns cobblestone into lava. Since it can accept up to 20 MJ/t you are fine and you get 90% of the energy back. Another option is connecting a rolling-machine to your network. The rolling-machine draws 1 MJ/t permanent and will also stop the engines from overheating. Propably the best solution is to attach some energy-cells in a way that they can input and output to your network, so that they only fill after the machines storage is full. So even if the engine overheats the machines will drain the cells if they have work again and you have a rather large time to whack the engines before the machines stop working.
Technically overheating is only a problem in automated systems that do not need permanent power-supply. For manual setups you can just whack the machines with the hammer if you want to use them. Gates are great for most engines but not for the Magmatic Engines, since you do not want to turn it off. It needs a rather long time before it get's back to full efficiency so turning it on and off on demand wastes propably more MJ than turning cobble into lava to refill it (technically you can also use Netherrack to even get more lava, but you need to ensure a constant supply).
But there is a reason why engines connected to conduits normally do not overheat. Conduits have some kind of internal storage too. So even if all your power-storages are full it takes a while to fill large conduit-nets and only if that happens the engines start overheating. You can see that quite often if you attach them directly to a machine. Let's say you want to pump lava from the nether and move it via enderchests and cells. For this you need a liquid transposer to fill them, which is quite easily powered with a magmatic engine (since you pump lava anyway). If for some reasons the transposer did not get new empty cells it's storage fills up and it is very likely that the engine will overheat before you come back.