Dig out the other raspberry Pi and setup Raspbian Desktop.
Get the Arduino and hook up the Temp sensor. Tap into the Diesel Heater controller to see if it can be run from the Pi. A fuel level sensor is hooked up to the tank and it should be easy to hook that up to a GPIO pin.
3 raspberrypi 192.168.1.101 B8-27-EB-9D-EC-54