I have the same problem. Jeep runs great til after about 20 minutes of driving and then about then is when it hits 200 and does nothing but climb higher towards the red zone. So I turn on the heater and drive a little more carefully and it slowly drops back down to 200 but never back under. Took it into the shop and they fixed my small coolant leak and replaced a few hoses and it still does the same. So I brought it back and was told it is probably my radiator, since the water pump has been replaced. And I do not have that kind of money! It's a 1990 also. Would that cap fix my problem as well?

 

Possibly. $10 or less, and you should have it on there no matter what.

 

Okay I bought it on my way home from work so fingers crossed! Also, my oil gauge moves around A LOT. Do you know what could cause this? Sorry I know its off topic!

 

Oil gauge from where to where. Hot and cold.

 

Just randomly it moves up and down anywhere from below 40 to 60 back to 40 and it does this all the time

 

Normal for it to increase when the engine speeds up and drop when the engine slows down. The oil pump is driven by the engine and changes speed along with it. 40-60 is absolutely fine.
If it's wandering around with a steady engine speed, could be loose/dirty connector at the sensor, or a sensor that's beginning to fail, or a faulty connection somewhere in the wiring or ground to the gauge itself. Big plug on the firewall comes to mind as a possibility.

 

Hugh ?

 

Hugh? As in Hugh Hardon?

 

No as in oil gauge hot or cold...