I own no macks but have worked on them for awhile, 17 years. I am master Mack certified and Volvo as well, Mack for 15 years running. I used to be master G2 certified on Mercedes and Detroit but our dealership lost the affiliation. I have been master certified in cummis but have not renewed since 07. I work on Mack and Volvo mostly now. My passion is for hot rods. Building a 31 model a with a hilborn efi 325 dodge hemi. It is more fun to work on the trucks!
Yes you should hear the fan at anything above 85%. Was the fan always a viscous fan? If it was changed from a different drive it will need to be programmed for the correct over drive % and fan surface area as well as what the eecu is reading from thefan harness. If it always was a viscous fan then is sounds like there might be a problem with the 5volt reference. The boost temp and pressure sensor, egr delta p, and fuel pressure sensor all are Sharing the same 5volt reference from the eecu. The egr delta is the common issue with messing with signals on the reference line. Check the eecu plugs for oil as well. This shorts out the signals. The delta p wires will rub in the loom and short out causing the the fan not to work correctly and boost temps to read off. The regens will perform are they should as well. One more thing check for pin fretting I. All the connection on these sensors. If brown dust is found repair the pins or replace them.