Intermitten oil pressure problem
 

I have a 2000 ranger 4x4 3.0 flex fuel. The engine light came on on my way to work then the oil pressure gage went to zero followed by an undeniable ticking noise. The vehicle was parked and towed to a garage the next day. The mechanic said he found nothing wrong either cold, warm, at idle or highway speed. He changed the oil and told me that he found just the slightest bit of water but didn't think i needed to worry. I took it home but drove it very sparingly, then 2 weeks later i took it on the highway and within ten miles ... no oil pressure. i pulled over and let the truck sit with the engine off for 30 minutes before restarting. the oil pressure was back so i turned around and took it home where it has sat in my driveway ever since. I also found a yeloowish foam on the oil fill cap...

Any ideas here?

Could just be a bad Oil Pressure Sending Unit. These are a simple ON/OFF switched sending unit. You could install a manual pressure guage to verify if you're actually loosing pressure, or the sending unit is bad.

I considered that as a possibility except that the gage falling to zero was accompanied by a loud and very well defined ticking noise from the engine...