Could be worn out rings: knew of a Mercedes Diesel sedan, high milage with 3 drivers. Grandfather, son & grandson. When driven by grandson there was lots of blue smoke & it used oil. When driven by the son, it smoked a little on acceleration but used no oil. When driven by the grandfather (& original owner), it seldom smoked & made oil! Explanation was fuel leakage past the rings when babied, less leakage when driven normally & no leakage when the 18 y.o. tried to hot rod it. Don't know why the tractor only smokes after getting hot but you could be burning a little oil & replacing it with diesel fuel if this is a high hour tractor. Would be a good idea to change your oil often & sounds like a problem that may get worse over time. Don H