Nissan Repair: urgent, nissan frontier, oil gallery

Question
problems when engine oil gets in the radiaor for a 2000 nissan frontier

Answer
Saul,

The only way for engine oil to get into the antifreeze (radiator) is for something between the two to fail.  Most common problem is the headgasket.  The second would be a crack in the head where the oil gallery passes close to the water passage.  I would also say, if yours is an automatic and what you really have is transmission fluid in the antifreeze would be the cooler in the radiator for the transmission.  If you had an oil cooler and it was a oil to water cooler that could be a possibility too.