Autonomous

Short History: Just bought my 1999 2wd Cherokee two weeks ago w/ 86,xxx miles on it, so I have no history on it. Had the oil changed next day (5W30 Pennzoil). and have driven 800 miles so far. Oil is still at appropriate level, though appears very dark already.

Problem: The day right after the oil change I had a 10 minute ride home from work. As I pulled into my parking spot the oil pressure dropped to less than 10. Turned it off immediately, let it sit, then restarted, similar pressure. Went to bed, woke and checked oil, it was fine. Cranked the engine, oil pressure is perfectly normal at around 50, +/- 5.

Everything was normal for the next 2 weeks, then tonight when I started the engine, the oil pressure dropped again to around 10. Turned it off, let it sit, started it, same thing. Sat nearly an hour, trying it every 10-15 minutes, it goes between 30 and 40, I drive 5 minutes (halfway home) and stop, let it sit for 20 minutes. Crank it up, everything is fine at around 50.

My thoughts: I live in Houston, its 36 degrees right now. it was probably below 40 the first time, too. So, thinking perhaps the sensor is going out when it gets extra cold (relatively speaking, ofcourse). It has been colder a few nights, but the problem didn't happen then, only twice. 5W30 or even 10W30 shouldn't be too thick for Houston weather, where getting below freezing happens 5 times a winter. I'm stumped.

MS Fowler

When the gauge went to zero, was there any increased noise level from the engine?

If no extra noises, I would suspect the oil pressure sender or the connections.

Autonomous

I didn't hear anything new, no. Hopefully you are right, doesn't seem logical to me for a mechanical oil pump to break and magically mend itself twice. Seems more likely a weather-related electrical problem.

Ah well, tomorrow is payday, may have to hit up my favorite mechanic and see what he makes of it. Thanks for the input, MS Fowler.