oil gauge

Most likely a bad oil pressure sender unit but best to check and test the part before jumping to conclusions. If the part is cheap may be best to just replace it. Look at www.rockauto.com or a online parts source for parts price. Autozone have some popular workshop manuals for free on line once you register (for free) on their website http://bit.ly/autozone_repair_info

Sounds like you may have an oil pressure sender issue. However, a real base engine oil pressure reading should be done just to verify there is no other issue.