Apparent low oil pressure after coming off plane

[helix757]

I have a new to me boat that has a 6.2L MX MPI Mercruiser engine. Upon a cold start, the oil pressure gauge shows 35-38PSI. Once warmed up, it settles at about 20PSI. I cruise at about 3500RPM, and while cruising, oil pressure reflects 30-35PSI. However, I noticed when I get off plane when entering a channel, the oil pressure gauge drops to what looks like 6-8PSI. It slowly comes back up as I assume the oil cools. Temps at all times never go above 165, and the engine sounds fine -- no ticking or anything. Also, no alarms. Just the normal two beep test when key is turned to the on position for the system self-test.

Engine was professionally serviced including an oil change with a new filter.

Is this behavior normal?

I tested the gauge by tapping the signal stud to ground, and the needle does go to the max pressure. I am thinking about replacing the oil pressure sender as it does not look OEM. Also, I cannot seem to find the oil pressure switch for the alarm. It is not a "tee" fitting with the sender unit.

Any insight would be greatly appreciated!

 

[Chris1956]

Any idea what oil was put into the engine?

The oil pressure switch grounds when there is no oil pressure. Look for a "Peppermint Patty"-like device with a single wire on the block.

 

[helix757]

Any idea what oil was put into the engine?

The oil pressure switch grounds when there is no oil pressure. Look for a "Peppermint Patty"-like device with a single wire on the block.

Good question, texting my mechanic now. What oil SHOULD have been used?

I will take a trip down there to try to look for the pressure switch again.

 

[Scott06]

Good question, texting my mechanic now. What oil SHOULD have been used?

I will take a trip down there to try to look for the pressure switch again.

25W-40 quicksilver or equivalent. Not to turn this into an oil thread - you just dont want 5w-30 or any of the thinner oils typical of modern automotive use.

Given you are not getting an alarm- I would measure the OP with a mechanical gauge to vet the dash gauge. Would not be the first time a sender or gauge wasn't accurate.

Would also check the oil for signs of fuel contamination (smell)

 

[Scott06]

Good question, texting my mechanic now. What oil SHOULD have been used?

I will take a trip down there to try to look for the pressure switch again.

if it is the pre 2015 ish chevy based 6.2 the oil pressure switch will be by the distributor and as Chris stated single wire ground it and you should hear the alarm- not a bad idea to test

 

[helix757]

if it is the pre 2015 ish chevy based 6.2 the oil pressure switch will be by the distributor and as Chris stated single wire ground it and you should hear the alarm- not a bad idea to test

It is a an early 2000's for sure, probably the first generation to be honest.

Looking at the engine head on, the oil pressure sender is located on the back right, under the exhaust manifold.

Would the oil pressure switch be on the bottom side of the block too, or on the top side?

 

[Scott06]

It is a an early 2000's for sure, probably the first generation to be honest.

Looking at the engine head on, the oil pressure sender is located on the back right, under the exhaust manifold.

Would the oil pressure switch be on the bottom side of the block too, or on the top side?

on my 5.0 and 4.3s the sender and oil pressure switch(2wires- for the electric fuel pump) are in a T above the oil filter housing on block, the alarm is a seperate switch with one wire on the block just next to dist.

 

[helix757]

on my 5.0 and 4.3s the sender and oil pressure switch(2wires- for the electric fuel pump) are in a T above the oil filter housing on block, the alarm is a seperate switch with one wire on the block just next to dist.

Got it.

So on your engine, one switch cuts the fuel pump, the other switch, in another location, operates the alarm.