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04 Malibu LXI Oil pressure gauge sounding alarm

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I have an 04 Malibu LXI 340 Monsoon. I’ve searched several posts on this site regarding similar issues but I haven’t had any luck fixing mine. For years the oil pressure gauge will drop at idle/slow speeds and sound the alarm. Revving the engine brings the pressure back up or high speed. Usually there are no initial issues after a fresh oil change (rotella 15w-40 with K&N oil filter) but after a few hours it acts up. Seems to be more common once the engine warms up each time. 

The oil sending unit and oil pressure switch have been replaced in the past with no change. I’ve made sure the cannon plug is not over greased and spread out the connectors. The brass T fitting for the sending unit and sensor was replaced prior to me owning the boat. 

At the end of last season, the oil pressure gauge read high and the needle continued to slowly climb and spin almost all the way around the gauge. (This happened two seasons before and somehow fixed itself after the thermostat was replaced by the dealership). Not sure if this was a coincidence? The gauge is currently stuck all the way around. 

I’m trying to decide if I should try replacing the sending unit and oil sensor again but don’t want to keep wasting my money. I see there is a Indmar digital oil pressure sending unit ($160) I’ve never replaced, could the be the problem? 

Any further suggestions or tips would be greatly appreciated. Every season I try and trouble shoot this issue without any success! 

Thank you, 

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Thanks for the quick response!

So if the manual gauge reads normal pressure, I can assume it’s an electrical issue and would need to continue the process of elimination? Any suggestions on what I would look at after that? 

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Assuming you have a Medallion system, you could swap any two gauge wires to see if it changes the oil pressure readings or if that is truly pooched.  Of course the manual gauge will at least tell you there is no engine issue.  Assuming it shows the correct pressures.  My old gauges  was only ever correct when the boat was turned off.  :)

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I put a small  1" mechanical gauge on my engine when new.  A nice piece of insurance. Just be sure to use a glycerin filled gauge.

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Thanks electricjohn- I might want to do that as well. Do you change the brass T fitting so you can add a spot for the mechanical gauge?

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I added a second tee or installed an X, don't recall, long time ago.

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