Easy with the straight power to the battery. A sudden spike and the ECU will be fried.
A heat issue usually makes me think of the CPS...then again, I blame that for every non-start issue. lol
If you're getting low voltage to the ECU, you could have bigger issues. One thing to note is that the coolant temp sensor will keep the motor from firing up if the sensor "thinks" the motor is too hot. Since the gauge indicated a high heat issue, you may want to change that sensor. Also be sure that the fan(s) kick in when the needle gets above your gauge's normal range (all cars are not the same, even the same cars).
So, the two things I recommend are the CPS and temp sensors and remove the jumper as soon as possible. If it is a voltage issue to the ECU, the fix isn't to jump it, but to find the voltage draw. I know time is of the essence, but the time will lengthen and the headaches will get bigger if the ECU fries.