Oil gauges are notorious for reading low. Check the oil level, and use your ears. If the pressure is low, these motors will tell you.
Your temp sensor is shot. It is the green wired sensor in your thermostat housing. I may have some good ones.....
For now, just unplug it. the fan should run if the key is on
third problem could be coupled with the second. maybe your thermostat is bad?
--Russ