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Odd Oil Pressure Problem mercury 5.7 efi with bravo 3

N

njboatman

New member
I have reviewed almost every thread that I can find on oil pressure and none of them address the issue that I am having. I have a remanufactured mercury 5.7 EFI with a Bravo 3 outdrive. The motor has about 80 hours on it, I will state I have changed the oil twice (mercury oil per manual), the oil filter 3 xs and verified the readings with a mechanical gauge.

I start the motor and I have 40 lbs of oil pressure, if I let it idle the pressure will drop down to about 20 lbs at idle, but pop up to 30 lbs at 1000 rpm. It will do this all day if I never go above 1200 rpms or so. If I take the boat up to cruise at 3200 rpm it will have 40 lbs of oil pressure the entire time I am at 3200 rpm. If I stay at 3200 rpm for 2 minutes or 22 minutes still 40 lbs of pressure, the moment I slow down the oil pressure drops to about 5 psi at 1000 rpm and 0 on the gauge at idle. If I start back up to 3200 rpm it will come back up to 25 lbs, but never to 40 lbs.

If I run to 3200 rpm for 1 minute it does the same thing. I appear to lose all pressure the second I slow down after cruising regardless of how long I cruise, if I shut the motor off and wait an hour I can duplicate the result, whatever the issue is it resets itself after sitting.

Any Ideas?
 
My first guess based on "remanufactured"

Weak oil pump or loose tolorance on crank shaft at mains...and or rods to crank....

If spacing is to much on crank between main cap crank and or rod to crank, it can cause low oil pressure.

I could be wrong as this is not a common issue these days.

Most marine small blocks i see run 40-60 psi.
40 when hot.

My truck with 150000 miles acts like your engine.
40 ish cold but after hot can go down to 10 psi...
Been that way since i bought it with 100000 miles.

Chevy spec....5 psi or greater....
 
If you want to get a bit more out of it this boating season, add a full can of Lucas Oil Extended. That will provide enough additional oil pressure to keep it going--for a while--but in the long run that motor has to come out.

Sorry,

Jeff
 
Sudab6 said:
Was the oil pump primed before first start after motor was built ?
Click to expand...

I dont know the answer to that,the motor was installed by marinemax for the prior owner. On the sea trial they started the boat and it showed good pressure and we only ran it up once, I did notice it was low on the way in, but I shrugged it off as a bad sender and the sellers assurance it was a non issue. Shame on me for moving forward without an investigation.
 
First thought I have is to verify witha mechanical guage that the pressure is accurate. Have seen similar symptoms -pressure drops after long high speed run - in older high mileage engines and as mentioned have band aided with higher viscosity oil or Lucas. This is only a crutch if oil pressure is low rebuild wasn't done right
 
..."Was the oil pump primed before first start after motor was built ? "

That would be irrelevant by now. There's something seriously amiss inside there.

Jeff
 
fastjeff said:
..."Was the oil pump primed before first start after motor was built ? "

That would be irrelevant by now. There's something seriously amiss inside there.

Jeff
Click to expand...

2X on this.

Either way that engine is coming out.

I know you said it was checked with a mechanical gauge, What type of mechanical gauge was used?
 
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Docksidemarineservices said:
2X on this.

Either way that engine is coming out.

I know you said it was checked with a mechanical gauge, What type of mechanical gauge was used?
Click to expand...

i dont see where the OP said he checked it with a mechanical gauge, if the OP didn't do that, it should absolutely be done befre any engine repair be undertaken. i had an OMC this summer that lost oil pressure after a run, turned out to be a bad sensor.
 
You have to pull the oil pan and check the mains and rod bearings .plasitgauge
And check tollerances within specs. Check oil pump mounting and for cheap $$ dollars change the pump. Do not use a high output pump.
 
mcomm said:
Oil pump pressure regulator may be sticking, replace pump before tearing engine apart.
Click to expand...
This makes sense because he doesn't have a problem until he slows down and the pressure would naturally drop. The pressure regulator may be sticking in the position it should be in under high pressure, and when the engine slows down, this causes pressure to drop.
My old '88 runs at 40 psi cold idle, at 3500 rpm it is at about 58 psi, hot slow idle is between 20 and 30 psi. If I put it back up on plane it will jump back up to 58 psi. Running Merc 25/40 oil with a Mercruiser/Quicksilver oil filter.
 
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Not sure if this helps but..

The great Smokey Yunick stated that an engine needs 10 psi oil pressure per thousand rpm. I hope your engine had enough to prevent bearing damage.

Jeff
 
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