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5.7 Indmar Dropping Oil Pressure


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We have another challenge with our 2003 Wakesetter VLX, 5.7 Indmar, Monsoon 325  

We were chasing some bad oil pressure readings and electrical issues, so we’ve in the process replaced the multi gauge, the oil pressure sender, and oil pressure switch. Even checked out all the wiring and grounds, and even replaced the MMDC.  All boat systems work great now, except a new oil pressure reading issue had popped up  

Replacing all the above did help stabilize the oil pressure, but now when we give it throttle and load the engine, about half the time we’re seeing the oil pressure completely drop out and, the ‘no oil pressure’ alarm sounds. 

When the throttle is reduced, the oil pressure comes right back up to normal. 

We’re going to be setting up a mechanical oil pressure gauge this weekend, but I wanted to know if anyone has seen such an issue before. 

After some research and even an email from Indmar, we put an extra quart of oil in (over the full mark) in an effort to make sure the oil pump wasn’t starving. That made no difference. 

We’re running synthetic 15w-40 with a Purple Power oil filter; all with maybe 50 hours on this oil/filter. 

Any ideas?

Thanks for the help!

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With me, it's usually the cannon plug.  I do have a mechanical gauge on the engine.  If you put one on, make sure it is glycerin filled. I have no pressure issues even if a quart low.

Edited by electricjohn
  • Like 2
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Thanks for the reply.  
I forgot to say that as part of the overhaul and along with all our new parts mentioned above, we replaced the cannon plug with an 8 pin marine connector.  We didn’t want to take any chances going forward, after hearing all the headaches about the cannon plug. 
So we should be all good for connections from the engine harness to boat harness now. 

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So we got the mechanical oil pressure gauge on it. 
There’s nothing wrong with the engine’s oil pressure system. We get good steady oil pressure...65 psi at idle. 
However, while the pressure is rock solid on the mech gauge, both the oil pressure gauge (on the multi gauge) and the oil pressure switch are not working correctly.  The oil pressure is fluctuating up and down and the Speedo LCD reads “no oil pressure” when the oil pressure gauge reads zero. 
So something is telling both the sender and the switch that the oil pressure is dropping off and rising again, repeatedly. 
We tried putting a ground wire from the body of the sender to ground on the engine, but didn’t make a difference. 
What could be sending incorrect pressure signals to BOTH the sender and the oil pressure switch?

any ideas??

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My dash gauge acts very similarly to yours. Put the mechanical gauge on it and it was rock solid like yours. My dash gauge can go low but not below about 30lbs., and then back up to 60ish and maybe a little more. It does this as I add load. Within a moment it goes back up to 60. I wonder if it's a ground issue of some sort. Right now, my engine seems to be running better than I have ever had it.

Steve B.

Edited by Steve B.
added thought
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The MMDC gauge control only sends 5 volt to your senders to give you a reading to ground. The current range is only 4 to 20 milliamps.  Any poor connection will effect this low power signal.  Michael, what makes you think the oil switch is not functioning properly?

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I sometimes have the opposite thing happen on my boat. Oil pressure will fluctuate, and occasionally if I accelerate, the gauge will spike to 80psi. I'd like to think it's just the gauge acting a little funky. (The fuel gauge does the same thing when I really punch it, even after I hold the speed for a few minutes).  At idle everything stabilizes and is fine. The malibu owners manual even says the oil psi can fluctuate from I believe 7 psi - 40 psi when running at idle speeds. A little weird, right? 

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  • 1 year later...

How did you go? I have the same happening, I just tried to clean the oil pressure switch on the engine. but it hasn't worked

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5 hours ago, Jawsmovie77 said:

How did you go? I have the same happening, I just tried to clean the oil pressure switch on the engine. but it hasn't worked

It might also be worth your time to clean and inspect the Cannon plug (engine harness connector).  Depending on the connector you have, either the male pins or the female sockets use spring tension to ensure a good connection.  Sometimes they need the springy parts bent back out a little.

You also can't go wrong with a thorough cleaning of every connection under the dash.  Vibration and oxidation lend themselves to crud building up between conductors, which eventually makes electronics get funky.

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Like Gary said...cleaning the canon connector on my 95 solved my oil pressure gauge bouncing around issues.

Steve B.

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When I had my 5.7 Monsoon, 2002, I had to change out my oil pressure sender and switch.  The brass colored sender was changed more than once over the 18 years I owned that boat. 

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