I am experiencing erratic readings on the Mechanical Oil Pressure Gauge on My New. Engine. Been driving several Times and Gauge shows consistent 55-60 PSI at 50 MPH. Yesterday it started acting erratically. . 60 30 20 0 25 30 etc. there is pressure because Oil is getting to Heads and Dash Light has not come on . I have ordered a cheap tester from Amazon for Sat to see what it shows. Oil Pump is new with no Air Leaks etc. Checked all that. wondering if relief Valve is stuck open maybe.. The Pump should be good as it is pumping pressure to Heads. Is there a problem checking relief Valve and putting back together with existing Gasket? I will check pressure with Gauge Saturday. 

  

The first thing I would check would be the rubber seal at the inlet to the oil pump. Simply try tightening that gland nut some more and see if the oil pressure becomes consistent once more.

Lorena, Texas (South of Waco)

Done that. Check all possible points of Air Entry. This is a New Mellings Pump by the way. Up until Yesterday all was registering properly. As I mentioned there is pressure at Idle because Oil is flowing to Head.I am using the all Rubber sleeve on Oil Tube to Pump as supplied by Best. Any reason to use the One with metal Sleeve?  Should I open up relief Valve and make sure it is free? Thanks Ted

  

Zero oil pressure with the oil relief valve stuck in an open position would be unusual.  If the oil pressure is swinging up and down, pulling air in on the inlet side of the pump is still high on the list as the probable cause.

The oil pump relief valve can be removed with the pump still on the engine.  It’s questionable if the oil relief valve gasket can be reused so having one of those handy when doing this is advisable.  If the gland seal at the oil pump inlet is the Fel-Pro version, then that one has the metal collars on it and can be problematic in sealing.  That particular gland seal is also known to deform the oil inlet tube where it goes into the oil pump which will also create a sealing issue later down the road even if a non-metal collar seal is being used.  I have made a swedging tool that will re-straighten those inlet tubes when they are deformed.

Lorena, Texas (South of Waco)

Thank You Ted. I have a test Gauge coming Today and will verify the problem. I agree it would be very unusual for a new pump to get stuck in open position. I have an extra Pipe to Pump Seal. Let You know the result. 

  

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I took the inlet Pipe apart and re-installed it Today. Just satisfy my mind that is was not the Problem. Wasn't. Still doing it. Now I think it's just the Gauge that has gone south. I got a test Gauge from Amazon Today. Check it Sunday. The Idiot Light on Dash never came on at all which is why I am leaning towards bad Gauge. Stewart-Warner expensive Gauge. Mechanical. was working fine. Then it quit .Let U know outcome.

  

Still got low to no Oil Pressure on Test Gauge. When I started this Engine initially it had 55-60 PSI Cold and ran consistently  with Steady Oil Pressure. Thursday the Gauge starting acting erratic. 60 40 0 20 etc. Replaced the Seal on pickup Tube Yesterday. . No difference. Tested Today with manual Gauge still showing same problem. There is Oil Flow because Heads are getting Oil  and the Idiot Light has not come on at all even with Low Gauge reading. What do I look at now? Oil Relief Valve on Pump? New Melling Pump. Not sure where to go now. Suggestion? Wondering if the Oil Pump itself is the problem?  Relief Valve maybe.? No external Leaks on Engine and it was fine until Thursday.

  

What is inside the Oil Pump besides Gears? Any check Valves or Similar I have never opened One up. When Engine Starts it shows 60 PSI and within 15 Seconds it drops. I am at a loss to understand what has happened?   I opened up relief Valve and spring looks fine, Haven't pulled the piece inside until I got a Magnet to pull it out. Really need some Suggestions. Thanks! Wondering if I have bad Oil Filter possibly? Would a bad Filter cause similar Symptoms?

  

You are going to have to wait for TED to come on for the final word. He has seen more than most.

Be advised that if that seal is not installed correctly and/or is not a quality part (or the tube is bent), the pump will suck outside air leading to aeration and failing oil pressure.

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