I have a 2001 Cherokee that used to be a Fire Prevention car for the state of Colorado so it had very low miles when I bought it (65k in 2020). Recently I've been having issues with my oil pressure gauge dropping at idle and then popping back up once I accelerate. This only happens after driving the car for about 30 minutes or so. I have a new radiator (a few months old now) and I recently changed my oil and filter and it is still occurring. On top of this I feel like my coolant is draining somewhere, I have to refill it every few months but I can't find any drips or leakage. I changed the radiator in hoping to solve this but no luck I guess. Any advice is welcomed.

 

Mystery coolant loss on 2000/2001 is usually a sign of a cracked 0331 head. Get an coolant exhaust gas and compression test done.

What's your oil pressure at idle? Could be a bad sensor, could be a bad pump, could be a worn motor, could be a bad filter. If the motor was left running idling alot it could be low miles but have worn bearings.

 

Low Oil pressure at idle getting better with RPM's increasing is a classic indicator of bad main bearings, a worn out oil pump or a bad sensor/oil gauge - but it should happen all the time - not just after 30min. Check the sensor and the gauge - you'll need a shop manual and a VOM. Has the oil level on your dip stick risen? - that may explain where the coolant is going as a result of a bad head gasket. If not, then pressure test the cooling system. Good luck

 

Before panicking or throwing money at it put a mechanical oil pressure gauge on it to see what's going on and look in a shop manual as mentioned above to see what the numbers should be.

......and google jeep 331 head cracking to see how to look for the crack