Over advancement will cause overheating in a diesel. Had a tech at a local import store burn up 3 motors in a Volkwagon because he wasn't zeroing his dial indicator properly while installing the injection pump. IMHO 20 degrees seems a tad high and would seem to be getting into burn down range.
------------------
The smiling ex-dealer technician
89 w250, 47rh trans, cleaned up exhaust, Dynomax bullet muffer, 3" lift, unknown oversized injectors