Help! Low oil pressure and engine revving up a few hundred RPMS

[bmay1909]

I have a 2004 Sea Ray Sundancer 320 with Mercruiaer 6.2 MPI inboard engines.

While out yesterday after about 20 minutes of cruising at 3700 RPMs and then idling for about 10 minutes I went to get back on plane and noticed my starboard pressure dropped to around 10 PSI and would slowly increased to 30 PSI and would fluctuate quite a bit. At about 1800 RPMs the RPMs on the starboard engine would ramp up a few 100 and then lower a few 100 RPMs and continue to ramp up and down. Ended up idling back to the slip. Any ideas what could be causing this?

 

[Rick Stephens]

Dirty grounds?

 

[alldodge]

Or bad gauge/sender
Put a mechanical gauge Tee'd into where the sender is and verify if you have a pressure issue or other

 

[bmay1909]

Dirty grounds?

How is do I determine if it’s dirty grounds? Sorry new to this

 

[bmay1909]

Or bad gauge/sender
Put a mechanical gauge Tee'd into where the sender is and verify if you have a pressure issue or other

Where is the sender located?

 

[alldodge]

Dirty grounds can be anywhere there is a ground connection. Behind the helm, on the motor, about anyplace

The oil pressure sender should be next to the oil pan on the port side. There will be one if not to senders connected to the block 1/8 NPT port. Just need to add another Tee so a mechanical gauge can be used

 

[epjohnson]

What is the viscosity of your oil? I'm not sure about the newer engines, but my 1989 5.0 OMC(302 Ford)would do the same thing as far as pressure goes until my buddy turned me onto Marine 20w-50w, 4 cycle engine oil from Autozone. Afterwards, my pressure was 30 at idle and about 50 at 3000rpm cruising.

 

[bmay1909]

Dirty grounds can be anywhere there is a ground connection. Behind the helm, on the motor, about anyplace

The oil pressure sender should be next to the oil pan on the port side. There will be one if not to senders connected to the block 1/8 NPT port. Just need to add another Tee so a mechanical gauge can be used

Would this cause the fluctuation in RPMs I was receiving when at 1800/1900 RPMs?

 

[bmay1909]

What is the viscosity of your oil? I'm not sure about the newer engines, but my 1989 5.0 OMC(302 Ford)would do the same thing as far as pressure goes until my buddy turned me onto Marine 20w-50w, 4 cycle engine oil from Autozone. Afterwards, my pressure was 30 at idle and about 50 at 3000rpm cruising.

I'm using Quicksilver Oil 25W40. Oil and filters were changed back at the beginning of July. Since then I have put about 40 hours on when I received the drop in pressure.

 

[alldodge]

Would this cause the fluctuation in RPMs I was receiving when at 1800/1900 RPMs?

If there is a bad connection anything is possible. If its on the gauge or the gauge wires, then the gauge moves around. If its on the main power lines, then voltage is reduced and when that happens the spark is reduced and so does combustion power and reduced rpms

 

[bmay1909]

If there is a bad connection anything is possible. If its on the gauge or the gauge wires, then the gauge moves around. If its on the main power lines, then voltage is reduced and when that happens the spark is reduced and so does combustion power and reduced rpms

So there's no 1 place I should be looking for a bad connection/bad ground, basically trial and error correct?

 

[Scott Danforth]

Start at the battery, and clean/tighten every connection all the way to the help and back

 

[alldodge]

Correct
Best method is to start at the batteries, remove cables at both ends and start cleaning to shinny metal. This includes the black ground cables where it attaches to the block.

Then the 10 pin engine connector and up to the helm

 

[bmay1909]

Correct
Best method is to start at the batteries, remove cables at both ends and start cleaning to shinny metal. This includes the black ground cables where it attaches to the block.

Then the 10 pin engine connector and up to the helm

Thank you, appreciate the assistance! Hope I can get this figured out

 

[bmay1909]

Correct
Best method is to start at the batteries, remove cables at both ends and start cleaning to shinny metal. This includes the black ground cables where it attaches to the block.

Then the 10 pin engine connector and up to the helm

Where would my oil pressure sending unit be located at?

 

[alldodge]

Where would my oil pressure sending unit be located at?

Down low on the port side near the stern attached to the block.

 

[bmay1909]

Down low on the port side near the stern attached to the block.

So the mechanic came out to the boat today to see if he could figure out what's going on. Unfortunately, he thinks is some type of loose bearing. He continued to have the same oil pressure readings on his computer.

He believes its a loose bearing of some sort (mentioned cam bearing, rod bearing and a few other types of bearings. When he increased the RPMs to 2300 he heard a lot of knocking.

Telling me were gonna need to pull the engine and tear it down to see what exactly is causing this.


Any suggestions?

 

[alldodge]

When he increased the RPMs to 2300 he heard a lot of knocking.

That's the key word "knocking" which in most cases its bearings, and if I ever heard knocking its rebuild time

Before there was a possibility of bad sensor, but not now. You need another motor or rebuild yours.

I have a Merc reman in the barn with about 70 hours with a spun bearing

 

[bmay1909]

That's the key word "knocking" which in most cases its bearings, and if I ever heard knocking its rebuild time

Before there was a possibility of bad sensor, but not now. You need another motor or rebuild yours.

I have a Merc reman in the barn with about 70 hours with a spun bearing

Bummer. Our short boating season just got a lot shorter.....


Can you DM the details of your Merc reman?