Most machines that run on EU also blow up if they are given too much.
The only exception I know of is the Electric Engine from Forestry, that does who knows what with the extra EU it recieves.
(If someone knows that one, go for that as well. Does it buffer the extra and use it, or just waste it?)
Your question touches on the mechanics of how the IC2 e-net works. And it doesn't work like you think it does
When a machine is said t be able to accept a certain amount of EU/t, in 99% of the cases that's a misnomer and should be written as EU/p. As in, EU packet size. The electric engine doesn't care about the packet size it receives. However, that doesn't make any statement about actual EU going into it.
The e-net works like a client-server network. The client (the electric engine) says, in a random example, "Send me the 100 EU I need to top off my internal buffer". The server can be any e-net component capable of sending packets. Let's assume a MFE. It receives the request for EU, and examines the request size: 100 EU. But the MFE can only send packets sized 128 EU. Therefore it does nothing.
One tick later, the electric engine (consuming 6 EU/t) will then ask for 106 EU to top itself off. The tick after that, 112. Then 118. Then 124. Then 130. Aha! The MFE says, "130? I can do that!" And sends one packet sized 128 EU. The electric engine receives it, and one tick later, it asks for 8 EU (2 were not topped off, plus six for one tick of operation). Then 14. Then 20. And so on, until something in the e-net can once again send a packet.
It's difficult to say what exactly happens if you hook up an eletric engine to a HV transformer outputting 2048 EU/p. I don't know how the engine works internally, I don't think I've ever used one. The first instinct would be to say an internal buffer of at least 2048 EU, but the engine is able to handle an arbitrary packet size, and the buffer can't be arbitrarily sized. Or can it? Maybe the engine requests a single packet of "whatever you can throw at me", buffers it, consumes it fully and then asks for another. But that would have to be tested.
Back on the electric engines... what causes them to overheat?
Is it just running time or does it have something to do with the actual work load it is applied against?
Your question touches on the mechanics of how the Buildcraft power framework works. (Deja vu?
)
A Buildcraft compatible engine generates MJ every tick, but only outputs in bursts when the piston reaches the apex of its stroke. Some engines can try to transfer between 100 and 200 MJ with each burst, and not every Buildcraft compatible device can accept that much at once (some examples of burst input limits: Pump, 10 MJ; Refinery, 25 MJ; Redstone Energy Cell, 1-100 MJ; Quarry, 25-500 MJ; Redstone Conduit, 1000 MJ). The energy that cannot be transferred in that burst remains in the engine and fills up the internal buffer, causing the engine to change colors and stroke faster (exception: combustion engines scale by temperature, not internal energy). A faster stroke speed means smaller bursts are sent more often, which is a way to try and overcome the input limit of the receiver. However, if you attach the wrong engine to the wrong thing, at some point it may hit 100% on the internal buffer and what happens then depends entirely on the engine in question.
(Electric engines won't explode, but it's possible that they shut off and enter a long forced cooldown, or need to be broken/replaced, or manually fixed in some other way.)