No oil Pressure, with knock. then oil pressure returns after turning off engine for a few minutes and cranking back up again.

if you ran out of oil and you now can hear knocking sound comming from the engine then it time to get it checked by a mechanic

Pull the sump and check the main bearings for spinning in cap. The knock indicates a bearing and the fluctuating pressure indicates a oil hole being opened and closed as the bearing shell moves over the oil hole in the crank.

Knocking in engine and low oil pressure usually means bad main bearings. May have been caused by bad oil pump or just worn out bearings due to high mileage. If this is problem needs engine or rebuild old engine.

oil pump gears inside the lower engine, or electrical. 1st make sure its full on oil, then sheck it with another pressure guage to confirm its not actuall pressure.

sending unit may be bad. If engine is not knocking or tapping when pressure reads 0 likely that's the case.

You need to replace the oil pressure sending unit, this is what tells your gauge what the pressure is. For future information if your oil pressure drops again and its a real failed oil pump within a few minutes you will internally damage the engine. I would get a new Oil Pressure Sending Unit. Let me know if you have any questions.... Thanks!

The first thing I would do is change the oil filter. Also, what engine do you have.

Locate your oil pressure sending sensor... generally near the oil filter intake but not always... give it a spray of WD40 to repel any water on it. next have the oil pressure tested just to be certain. the relay for the sending unit may need to be replaced as well... it's located likely in the fuse box in the engine compartment near the battery.

Robert

Please take a moment to rate this solution.. thanks

no oil on ground oil still full but after it runs for a few minutes oil pressure drops

your oil pump is either weak or there is sludge i9n the oil pan. my adives is to have the oil pan dropped . chances are sludge is the culprit. as the oil get's warm the pressure should only drop slightly but pressure is generally dictated by engine rpm. pumps are gear driven so if it was a bad pump your oil pressure would start out very low at start up.