It could be the matrix, but it's not a common failure where blocked plenums is. Also coolant has quite a strong smell so possible, but check the plenums first.
Temp gauge problem: no it's likely to be a problem with the
IPK. The information about engine temperature comes in via CAN
(Bus Controller Area Network), but so does the engine RPM. So of the tacho works, its not that. There's another thread live at the moment regarding a faulty temp guage. Carry out the checks suggested in that. If the temperature reads OK in the digital display, then its the same as in that thread, a faulty instrument pack. If the digital display also shows nothing, it could be the sensor in the engine, or a wiring problem.