1986 Jeep cherokee pioneer 2.8 V-6. Oil check is fine. But gage reads low.?

Replace oil pump.

what you hear clanking is the lifters that are dry. your oil pressure sending unit is not reading the the oil there because its not being PUMPED there. But the oil is all at the bottom of the pan thats why you still read you got oil. If its not the oil pump then you have debris stuck in a lube hole in the engine in wich case its not letting it flow. either case DONT DRIVE IT. unless you have the money for a new engine.

If you're hearing noises you haven't heard before, this is telling you that "yes, the oil press is low" and it's not just a gauge screwing up. How does the oil look? Is it black? Does it smell like gasoline? Is it muddy looking? These are signs that oil is dirty, contaminated with gasoline, or has water or antifreeze in it respectively. You might want to change your oil. If that's not the answer you might want to check into changing the oil pump and hopefully it's not too late! Those noises could be connecting rod bearings spining in the rod. NOT GOOD! You can take the oil filter off and cut it open and look for metal particles. If you find metal. Start looking for another engine.

Sounds like the oil pump is going out or has gone out.

Do not drive it.

Have the oil pressure checked.

The oil gage on your dash is a pressure gage and not a gage like the gas to tell you how much is there.