The engine does not reach the temperature

I have a transit of 2006 and for some time the temperature has usually been in 60 degrees after fast of working, in climbs it can reach 80 and in descents below 50 degrees and all this having covered the radiator. I have checked the thermostat and opens at 85 degrees and closes tightly. The thermostat of the oil cooler opens to 85 degrees and closes, does not close tightly since you blow through the tube let a little air pass (I do not know if it must be so). Ningumo of the two thermostats have signs of oxide.
Greetings and thanks,