This is my daughter's friend's Jeep (haven't seen it in person) and I'm told it's a '98 Cherokee with the straight six and 169,000 miles. He's in college and I'm trying to help over the phone. The dash guage drops to zero and the oil light comes on at idle once the engine warms up. There are no knocks or bangs from the engine. The guage reads about 40 PSI while driving.

It sounds to me like either the oil pump is shot or the sensor is no good. The first thing I'd do is add an external guage to the motor and see if it drops to zero when the dash guage does. Do these engines have a history of bad oil pumps? Is there anything else for me to suggest he have checked? Will he be OK to drive home from school (about 400 miles) and then his family's local shop can check it out? Thanks for any ideas.